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74,326 | 74,491 |
How should I detect unnecessary #include files in a large C++ project?
|
I am working on a large C++ project in Visual Studio 2008, and there are a lot of files with unnecessary #include directives. Sometimes the #includes are just artifacts and everything will compile fine with them removed, and in other cases classes could be forward declared and the #include could be moved to the .cpp file. Are there any good tools for detecting both of these cases?
|
While it won't reveal unneeded include files, Visual studio has a setting /showIncludes (right click on a .cpp file, Properties->C/C++->Advanced) that will output a tree of all included files at compile time. This can help in identifying files that shouldn't need to be included.
You can also take a look at the pimpl idiom to let you get away with fewer header file dependencies to make it easier to see the cruft that you can remove.
|
74,350 | 81,662 |
How to fix an MFC Painting Glitch?
|
I'm trying to implement some drag and drop functionality for a material system being developed at my work. Part of this system includes a 'Material Library' which acts as a repository, divided into groups, of saved materials on the user's hard drive.
As part of some UI polish, I was hoping to implement a 'highlight' type feature. When dragging and dropping, windows that you can legally drop a material onto will very subtly change color to improve feedback to the user that this is a valid action.
I am changing the bar with 'Basic Materials' (Just a CWnd with a CStatic) from having a medium gray background when unhighlighed to a blue background when hovered over. It all works well, the OnDragEnter and OnDragExit messages seem robust and set a flag indicating the highlight status. Then in OnCtrlColor I do this:
if (!m_bHighlighted) {
pDC->FillSolidRect(0, 0, m_SizeX, kGroupHeaderHeight, kBackgroundColour);
}
else {
pDC->FillSolidRect(0, 0, m_SizeX, kGroupHeaderHeight, kHighlightedBackgroundColour);
}
However, as you can see in the screenshot, the painting 'glitches' below the dragged object, leaving the original gray in place. It looks really ugly and basically spoils the whole effect.
Is there any way I can get around this?
|
Thanks for the answers guys, ajryan, you seem to always come up with help for my questions so extra thanks.
Thankfully this time the answer was fairly straightforward....
ImageList_DragShowNolock(FALSE);
m_pDragDropTargetWnd->SendMessage(WM_USER_DRAG_DROP_OBJECT_DRAG_ENTER, (WPARAM)pDragDropObject, (LPARAM)(&dragDropPoint));
ImageList_DragShowNolock(TRUE);
This turns off the drawing of the dragged image, then sends a message to the window being entered to repaint in a highlighted state, then finally redraws the drag image over the top. Seems to have done the trick.
|
74,451 | 81,493 |
Getting actual file name (with proper casing) on Windows
|
Windows file system is case insensitive. How, given a file/folder name (e.g. "somefile"), I get the actual name of that file/folder (e.g. it should return "SomeFile" if Explorer displays it so)?
Some ways I know, all of which seem quite backwards:
Given the full path, search for each folder on the path (via FindFirstFile). This gives proper cased results of each folder. At the last step, search for the file itself.
Get filename from handle (as in MSDN example). This requires opening a file, creating file mapping, getting it's name, parsing device names etc. Pretty convoluted. And it does not work for folders or zero-size files.
Am I missing some obvious WinAPI call? The simplest ones, like GetActualPathName() or GetFullPathName() return the name using casing that was passed in (e.g. returns "program files" if that was passed in, even if it should be "Program Files").
I'm looking for a native solution (not .NET one).
|
And hereby I answer my own question, based on original answer from cspirz.
Here's a function that given absolute, relative or network path, will return the path with upper/lower case as it would be displayed on Windows. If some component of the path does not exist, it will return the passed in path from that point.
It is quite involved because it tries to handle network paths and other edge cases. It operates on wide character strings and uses std::wstring. Yes, in theory Unicode TCHAR could be not the same as wchar_t; that is an exercise for the reader :)
std::wstring GetActualPathName( const wchar_t* path )
{
// This is quite involved, but the meat is SHGetFileInfo
const wchar_t kSeparator = L'\\';
// copy input string because we'll be temporary modifying it in place
size_t length = wcslen(path);
wchar_t buffer[MAX_PATH];
memcpy( buffer, path, (length+1) * sizeof(path[0]) );
size_t i = 0;
std::wstring result;
// for network paths (\\server\share\RestOfPath), getting the display
// name mangles it into unusable form (e.g. "\\server\share" turns
// into "share on server (server)"). So detect this case and just skip
// up to two path components
if( length >= 2 && buffer[0] == kSeparator && buffer[1] == kSeparator )
{
int skippedCount = 0;
i = 2; // start after '\\'
while( i < length && skippedCount < 2 )
{
if( buffer[i] == kSeparator )
++skippedCount;
++i;
}
result.append( buffer, i );
}
// for drive names, just add it uppercased
else if( length >= 2 && buffer[1] == L':' )
{
result += towupper(buffer[0]);
result += L':';
if( length >= 3 && buffer[2] == kSeparator )
{
result += kSeparator;
i = 3; // start after drive, colon and separator
}
else
{
i = 2; // start after drive and colon
}
}
size_t lastComponentStart = i;
bool addSeparator = false;
while( i < length )
{
// skip until path separator
while( i < length && buffer[i] != kSeparator )
++i;
if( addSeparator )
result += kSeparator;
// if we found path separator, get real filename of this
// last path name component
bool foundSeparator = (i < length);
buffer[i] = 0;
SHFILEINFOW info;
// nuke the path separator so that we get real name of current path component
info.szDisplayName[0] = 0;
if( SHGetFileInfoW( buffer, 0, &info, sizeof(info), SHGFI_DISPLAYNAME ) )
{
result += info.szDisplayName;
}
else
{
// most likely file does not exist.
// So just append original path name component.
result.append( buffer + lastComponentStart, i - lastComponentStart );
}
// restore path separator that we might have nuked before
if( foundSeparator )
buffer[i] = kSeparator;
++i;
lastComponentStart = i;
addSeparator = true;
}
return result;
}
Again, thanks to cspirz for pointing me to SHGetFileInfo.
|
74,696 | 75,346 |
On Windows Mobile device, what is the best way to display an OK button instead of the X button?
|
I have a C++ program that when run, by default, displays the X in the upper right corner. Clicking X, minimizes the program. I've added code using the SHInitDialog function to change the X to OK, so that clicking OK exits the program.
My question: Is there a better method that applies to the window, since SHInitDialog works best with Dialog Boxes?
|
With Windows Mobile 5.0 and higher, using the CreateWindowEx function passing it WS_EX_CAPTIONOKBTN for the extended style works.
@ctacke SHDoneButton may have also worked but I wanted to change the main window without handling it like a dialogbox, which is basically what SHInitDialog is doing.
|
75,180 | 75,202 |
How to display a dynamically allocated array in the Visual Studio debugger?
|
If you have a statically allocated array, the Visual Studio debugger can easily display all of the array elements. However, if you have an array allocated dynamically and pointed to by a pointer, it will only display the first element of the array when you click the + to expand it. Is there an easy way to tell the debugger, show me this data as an array of type Foo and size X?
|
Yes, simple.
say you have
char *a = new char[10];
writing in the debugger:
a,10
would show you the content as if it were an array.
|
75,191 | 87,648 |
What is an unsigned char?
|
In C/C++, what an unsigned char is used for? How is it different from a regular char?
|
In C++, there are three distinct character types:
char
signed char
unsigned char
If you are using character types for text, use the unqualified char:
it is the type of character literals like 'a' or '0' (in C++ only, in C their type is int)
it is the type that makes up C strings like "abcde"
It also works out as a number value, but it is unspecified whether that value is treated as signed or unsigned. Beware character comparisons through inequalities - although if you limit yourself to ASCII (0-127) you're just about safe.
If you are using character types as numbers, use:
signed char, which gives you at least the -127 to 127 range. (-128 to 127 is common)
unsigned char, which gives you at least the 0 to 255 range.
"At least", because the C++ standard only gives the minimum range of values that each numeric type is required to cover. sizeof (char) is required to be 1 (i.e. one byte), but a byte could in theory be for example 32 bits. sizeof would still be report its size as 1 - meaning that you could have sizeof (char) == sizeof (long) == 1.
|
75,213 | 75,262 |
scope resolution operator without a scope
|
In C++, what is the purpose of the scope resolution operator when used without a scope? For instance:
::foo();
|
It means global scope. You might need to use this operator when you have conflicting functions or variables in the same scope and you need to use a global one. You might have something like:
void bar(); // this is a global function
class foo {
void some_func() { ::bar(); } // this function is calling the global bar() and not the class version
void bar(); // this is a class member
};
If you need to call the global bar() function from within a class member function, you should use ::bar() to get to the global version of the function.
|
75,385 | 75,596 |
Make VS compiler catch signed/unsigned assignments?
|
The Visual Studio compiler does not seem to warn on signed/unsigned assignments, only on comparisons. For example the code below will generate a warning on the if statement but not the initial assignments.
Is there anyway to make it catch these? I'm already at W4 but thought (hoped) there may be another setting somewhere.
Thanks,
int foo(void)
{
unsigned int fooUnsigned = 0xffffffff;
int fooSigned = fooUnsigned; // no warning
if (fooSigned < fooUnsigned) // warning
{
return 0;
}
return fooSigned;
}
Update:
Quamrana is right, this is controlled by warning 4365 which appears to be off by default, even at W4. However you can explicitly enable it for a given warning level like so;
#pragma warning (4 : 4365)
Which results in;
warning C4365: 'initializing' : conversion from 'unsigned int' to 'int', signed/unsigned mismatch
|
You need to enable warning 4365 to catch the assignment.
That might be tricky - you need to enable ALL warnings - use /Wall which enables lots of warnings, so you may have some trouble seeing the warning occur, but it does.
|
75,432 | 75,452 |
How can I prevent URLDownloadToFile from retrieving from the cache?
|
I am using URLDownloadToFile to retrieve a file from a website. Subsequent calls return the original file rather than an updated version. I assume it is retrieving a cached version.
|
Call DeleteUrlCacheEntry with the same URL just prior to calling URLDownloadToFile.
You will need to link against Wininet.lib
|
75,701 | 78,235 |
What happens to global variables declared in a DLL?
|
Let's say I write a DLL in C++, and declare a global object of a class with a non-trivial destructor. Will the destructor be called when the DLL is unloaded?
|
In a Windows C++ DLL, all global objects (including static members of classes) will be constructed just before the calling of the DllMain with DLL_PROCESS_ATTACH, and they will be destroyed just after the call of the DllMain with DLL_PROCESS_DETACH.
Now, you must consider three problems:
0 - Of course, global non-const objects are evil (but you already know that, so I'll avoid mentionning multithreading, locks, god-objects, etc.)
1 - The order of construction of objects or different compilation units (i.e. CPP files) is not guaranteed, so you can't hope the object A will be constructed before B if the two objects are instanciated in two different CPPs. This is important if B depends on A. The solution is to move all global objects in the same CPP file, as inside the same compilation unit, the order of instanciation of the objects will be the order of construction (and the inverse of the order of destruction)
2 - There are things that are forbidden to do in the DllMain. Those things are probably forbidden, too, in the constructors. So avoid locking something. See Raymond Chen's excellent blog on the subject:
Some reasons not to do anything scary in your DllMain
Another reason not to do anything scary in your DllMain: Inadvertent deadlock
Some reasons not to do anything scary in your DllMain, part 3
In this case, lazy initialization could be interesting: The classes remain in an "un-initialized" state (internal pointers are NULL, booleans are false, whatever) until you call one of their methods, at which point they'll initialize themselves. If you use those objects inside the main (or one of the main's descendant functions), you'll be ok because they will be called after execution of DllMain.
3 - Of course, if some global objects in DLL A depend on global objects in DLL B, you should be very very careful about DLL loading order, and thus dependancies. In this case, DLLs with direct or indirect circular dependancies will cause you an insane amount of headaches. The best solution is to break the circular dependancies.
P.S.: Note that in C++, constructor can throw, and you don't want an exception in the middle of a DLL loading, so be sure your global objects won't be using exception without a very, very good reason. As correctly written destructors are not authorized to throw, the DLL unloading should be ok in this case.
|
75,722 | 75,755 |
Is there a better deterministic disposal pattern than nested "using"s?
|
In C#, if I want to deterministically clean up non-managed resources, I can use the "using" keyword. But for multiple dependent objects, this ends up nesting further and further:
using (FileStream fs = new FileStream("c:\file.txt", FileMode.Open))
{
using (BufferedStream bs = new BufferedStream(fs))
{
using (StreamReader sr = new StreamReader(bs))
{
// use sr, and have everything cleaned up when done.
}
}
}
In C++, I'm used to being able to use destructors to do it like this:
{
FileStream fs("c:\file.txt", FileMode.Open);
BufferedStream bs(fs);
StreamReader sr(bs);
// use sr, and have everything cleaned up when done.
}
Is there a better way in C# to do this? Or am I stuck with the multiple levels of nesting?
|
You don't have to nest with multiple usings:
using (FileStream fs = new FileStream("c:\file.txt", FileMode.Open))
using (BufferedStream bs = new BufferedStream(fs))
using (StreamReader sr = new StreamReader(bs))
{
// all three get disposed when you're done
}
|
76,796 | 76,844 |
General guidelines to avoid memory leaks in C++
|
What are some general tips to make sure I don't leak memory in C++ programs? How do I figure out who should free memory that has been dynamically allocated?
|
Instead of managing memory manually, try to use smart pointers where applicable.
Take a look at the Boost lib, TR1, and smart pointers.
Also smart pointers are now a part of C++ standard called C++11.
|
77,005 | 77,336 |
How to automatically generate a stacktrace when my program crashes
|
I am working on Linux with the GCC compiler. When my C++ program crashes I would like it to automatically generate a stacktrace.
My program is being run by many different users and it also runs on Linux, Windows and Macintosh (all versions are compiled using gcc).
I would like my program to be able to generate a stack trace when it crashes and the next time the user runs it, it will ask them if it is ok to send the stack trace to me so I can track down the problem. I can handle the sending the info to me but I don't know how to generate the trace string. Any ideas?
|
For Linux and I believe Mac OS X, if you're using gcc, or any compiler that uses glibc, you can use the backtrace() functions in execinfo.h to print a stacktrace and exit gracefully when you get a segmentation fault. Documentation can be found in the libc manual.
Here's an example program that installs a SIGSEGV handler and prints a stacktrace to stderr when it segfaults. The baz() function here causes the segfault that triggers the handler:
#include <stdio.h>
#include <execinfo.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
void handler(int sig) {
void *array[10];
size_t size;
// get void*'s for all entries on the stack
size = backtrace(array, 10);
// print out all the frames to stderr
fprintf(stderr, "Error: signal %d:\n", sig);
backtrace_symbols_fd(array, size, STDERR_FILENO);
exit(1);
}
void baz() {
int *foo = (int*)-1; // make a bad pointer
printf("%d\n", *foo); // causes segfault
}
void bar() { baz(); }
void foo() { bar(); }
int main(int argc, char **argv) {
signal(SIGSEGV, handler); // install our handler
foo(); // this will call foo, bar, and baz. baz segfaults.
}
Compiling with -g -rdynamic gets you symbol info in your output, which glibc can use to make a nice stacktrace:
$ gcc -g -rdynamic ./test.c -o test
Executing this gets you this output:
$ ./test
Error: signal 11:
./test(handler+0x19)[0x400911]
/lib64/tls/libc.so.6[0x3a9b92e380]
./test(baz+0x14)[0x400962]
./test(bar+0xe)[0x400983]
./test(foo+0xe)[0x400993]
./test(main+0x28)[0x4009bd]
/lib64/tls/libc.so.6(__libc_start_main+0xdb)[0x3a9b91c4bb]
./test[0x40086a]
This shows the load module, offset, and function that each frame in the stack came from. Here you can see the signal handler on top of the stack, and the libc functions before main in addition to main, foo, bar, and baz.
|
77,013 | 77,049 |
Which open-source C++ database GUI project should I help with?
|
I am looking for an open-source project involving c++ GUI(s) working with a database. I have not done it before, and am looking for a way to get my feet wet. Which can I work on?
|
How about this one http://sourceforge.net/projects/sqlitebrowser/:
SQLite Database browser is a light GUI editor for SQLite databases, built on top of QT. The main goal of the project is to allow non-technical users to create, modify and edit SQLite databases using a set of wizards and a spreadsheet-like interface.
|
77,126 | 77,147 |
What are some good compilers to use when learning C++?
|
What are some suggestions for easy to use C++ compilers for a beginner? Free or open-source ones would be preferred.
|
GCC is a good choice for simple things.
Visual Studio Express edition is the free version of the major windows C++ compiler.
If you are on Windows I would use VS. If you are on linux you should use GCC.
*I say GCC for simple things because for a more complicated project the build process isn't so easy
|
77,266 | 77,360 |
Can operator>> read an int hex AND decimal?
|
Can I persuade operator>> in C++ to read both a hex value AND and a decimal value? The following program demonstrates how reading hex goes wrong. I'd like the same istringstream to be able to read both hex and decimal.
#include <iostream>
#include <sstream>
int main(int argc, char** argv)
{
int result = 0;
// std::istringstream is("5"); // this works
std::istringstream is("0x5"); // this fails
while ( is.good() ) {
if ( is.peek() != EOF )
is >> result;
else
break;
}
if ( is.fail() )
std::cout << "failed to read string" << std::endl;
else
std::cout << "successfully read string" << std::endl;
std::cout << "result: " << result << std::endl;
}
|
Use std::setbase(0) which enables prefix dependent parsing. It will be able to parse 10 (dec) as 10 decimal, 0x10 (hex) as 16 decimal and 010 (octal) as 8 decimal.
#include <iomanip>
is >> std::setbase(0) >> result;
|
77,293 | 77,457 |
What is an easy way to create a MessageBox with custom button text in Managed C++?
|
I would like to keep the overhead at a minimum. Right now I have:
// Launch a Message Box with advice to the user
DialogResult result = MessageBox::Show("This may take awhile, do you wish to continue?", "Warning", MessageBoxButtons::YesNo, MessageBoxIcon::Exclamation);
// The test will only be launched if the user has selected Yes on the Message Box
if(result == DialogResult::Yes)
{
// Execute code
}
Unfortunately my client would prefer "Continue" and "Cancel" in place of the default "Yes" and "No" button text. It seems like there should be an easy way to do this.
|
You can use "OK" and "Cancel"
By substituting MessageBoxButtons::YesNo with MessageBoxButtons::OKCancel
MessageBoxButtons Enum
Short of that you would have to create a new form, as I don't believe the Enum can be extended.
|
77,817 | 77,911 |
C++ runtime knowledge of classes
|
I have multiple classes that all derive from a base class, now some of the derived classes will not be compiled depending on the platform. I have a class that allows me to return an object of the base class, however now all the names of the derived classes have been hard coded.
Is there a way to determine what classes have been compiled, at run-time preferably, so that I can remove the linking and instead provide dynamically loadable libraries instead.
|
Are you looking for C++ runtime class registration? I found this link (backup).
That would probably accomplish what you want, I am not sure about the dynamically loaded modules and whether or not you can register them using the same method.
|
78,053 | 78,866 |
How to iterate over all the page breaks in an Excel 2003 worksheet via COM
|
I've been trying to retrieve the locations of all the page breaks on a given Excel 2003 worksheet over COM. Here's an example of the kind of thing I'm trying to do:
Excel::HPageBreaksPtr pHPageBreaks = pSheet->GetHPageBreaks();
long count = pHPageBreaks->Count;
for (long i=0; i < count; ++i)
{
Excel::HPageBreakPtr pHPageBreak = pHPageBreaks->GetItem(i+1);
Excel::RangePtr pLocation = pHPageBreak->GetLocation();
printf("Page break at row %d\n", pLocation->Row);
pLocation.Release();
pHPageBreak.Release();
}
pHPageBreaks.Release();
I expect this to print out the row numbers of each of the horizontal page breaks in pSheet. The problem I'm having is that although count correctly indicates the number of page breaks in the worksheet, I can only ever seem to retrieve the first one. On the second run through the loop, calling pHPageBreaks->GetItem(i) throws an exception, with error number 0x8002000b, "invalid index".
Attempting to use pHPageBreaks->Get_NewEnum() to get an enumerator to iterate over the collection also fails with the same error, immediately on the call to Get_NewEnum().
I've looked around for a solution, and the closest thing I've found so far is http://support.microsoft.com/kb/210663/en-us. I have tried activating various cells beyond the page breaks, including the cells just beyond the range to be printed, as well as the lower-right cell (IV65536), but it didn't help.
If somebody can tell me how to get Excel to return the locations of all of the page breaks in a sheet, that would be awesome!
Thank you.
@Joel: Yes, I have tried displaying the user interface, and then setting ScreenUpdating to true - it produced the same results. Also, I have since tried combinations of setting pSheet->PrintArea to the entire worksheet and/or calling pSheet->ResetAllPageBreaks() before my call to get the HPageBreaks collection, which didn't help either.
@Joel: I've used pSheet->UsedRange to determine the row to scroll past, and Excel does scroll past all the horizontal breaks, but I'm still having the same issue when I try to access the second one. Unfortunately, switching to Excel 2007 did not help either.
|
Experimenting with Excel 2007 from Visual Basic, I discovered that the page break isn't known unless it has been displayed on the screen at least once.
The best workaround I could find was to page down, from the top of the sheet to the last row containing data. Then you can enumerate all the page breaks.
Here's the VBA code... let me know if you have any problem converting this to COM:
Range("A1").Select
numRows = Range("A1").End(xlDown).Row
While ActiveWindow.ScrollRow < numRows
ActiveWindow.LargeScroll Down:=1
Wend
For Each x In ActiveSheet.HPageBreaks
Debug.Print x.Location.Row
Next
This code made one simplifying assumption:
I used the .End(xlDown) method to figure out how far the data goes... this assumes that you have continuous data from A1 down to the bottom of the sheet. If you don't, you need to use some other method to figure out how far to keep scrolling.
|
78,717 | 79,071 |
"foreach values" macro in gcc & cpp
|
I have a 'foreach' macro I use frequently in C++ that works for most STL containers:
#define foreach(var, container) \
for(typeof((container).begin()) var = (container).begin(); \
var != (container).end(); \
++var)
(Note that 'typeof' is a gcc extension.) It is used like this:
std::vector< Blorgus > blorgi = ...;
foreach(blorgus, blorgi) {
blorgus->draw();
}
I would like to make something similar that iterates over a map's values. Call it "foreach_value", perhaps. So instead of writing
foreach(pair, mymap) {
pair->second->foo();
}
I would write
foreach_value(v, mymap) {
v.foo();
}
I can't come up with a macro that will do this, because it requires declaring two variables: the iterator and the value variable ('v', above). I don't know how to do that in the initializer of a for loop, even using gcc extensions. I could declare it just before the foreach_value call, but then it will conflict with other instances of the foreach_value macro in the same scope. If I could suffix the current line number to the iterator variable name, it would work, but I don't know how to do that.
|
You can do this using two loops. The first declares the iterator, with a name which is a function of the container variable (and you can make this uglier if you're worried about conflicts with your own code). The second declares the value variable.
#define ci(container) container ## iter
#define foreach_value(var, container) \
for (typeof((container).begin()) ci(container) = container.begin(); \
ci(container) != container.end(); ) \
for (typeof(ci(container)->second)* var = &ci(container)->second; \
ci(container) != container.end(); \
(++ci(container) != container.end()) ? \
(var = &ci(container)->second) : var)
By using the same loop termination condition, the outer loop only happens once (and if you're lucky, gets optimized away). Also, you avoid calling ->second on the iterator if the map is empty. That's the same reason for the ternary operator in the increment of the inner loop; at the end, we just leave var at the last value, since it won't be referenced again.
You could inline ci(container), but I think it makes the macro more readable.
|
78,723 | 79,169 |
How to test function call order
|
Considering such code:
class ToBeTested {
public:
void doForEach() {
for (vector<Contained>::iterator it = m_contained.begin(); it != m_contained.end(); it++) {
doOnce(*it);
doTwice(*it);
doTwice(*it);
}
}
void doOnce(Contained & c) {
// do something
}
void doTwice(Contained & c) {
// do something
}
// other methods
private:
vector<Contained> m_contained;
}
I want to test that if I fill vector with 3 values my functions will be called in proper order and quantity. For example my test can look something like this:
tobeTested.AddContained(one);
tobeTested.AddContained(two);
tobeTested.AddContained(three);
BEGIN_PROC_TEST()
SHOULD_BE_CALLED(doOnce, 1)
SHOULD_BE_CALLED(doTwice, 2)
SHOULD_BE_CALLED(doOnce, 1)
SHOULD_BE_CALLED(doTwice, 2)
SHOULD_BE_CALLED(doOnce, 1)
SHOULD_BE_CALLED(doTwice, 2)
tobeTested.doForEach()
END_PROC_TEST()
How do you recommend to test this? Are there any means to do this with CppUnit or GoogleTest frameworks? Maybe some other unit test framework allow to perform such tests?
I understand that probably this is impossible without calling any debug functions from these functions, but at least can it be done automatically in some test framework. I don't like to scan trace logs and check their correctness.
UPD: I'm trying to check not only the state of an objects, but also the execution order to avoid performance issues on the earliest possible stage (and in general I want to know that my code is executed exactly as I expected).
|
If you're interested in performance, I recommend that you write a test that measures performance.
Check the current time, run the method you're concerned about, then check the time again. Assert that the total time taken is less than some value.
The problem with check that methods are called in a certain order is that your code is going to have to change, and you don't want to have to update your tests when that happens. You should focus on testing the actual requirement instead of testing the implementation detail that meets that requirement.
That said, if you really want to test that your methods are called in a certain order, you'll need to do the following:
Move them to another class, call it Collaborator
Add an instance of this other class to the ToBeTested class
Use a mocking framework to set the instance variable on ToBeTested to be a mock of the Collborator class
Call the method under test
Use your mocking framework to assert that the methods were called on your mock in the correct order.
I'm not a native cpp speaker so I can't comment on which mocking framework you should use, but I see some other commenters have added their suggestions on this front.
|
79,023 | 79,050 |
Is there a C++ gdb GUI for Linux?
|
Briefly: Does anyone know of a GUI for gdb that brings it on par or close to the feature set you get in the more recent version of Visual C++?
In detail: As someone who has spent a lot of time programming in Windows, one of the larger stumbling blocks I've found whenever I have to code C++ in Linux is that debugging anything using commandline gdb takes me several times longer than it does in Visual Studio, and it does not seem to be getting better with practice. Some things are just easier or faster to express graphically.
Specifically, I'm looking for a GUI that:
Handles all the basics like stepping over & into code, watch variables and breakpoints
Understands and can display the contents of complex & nested C++ data types
Doesn't get confused by and preferably can intelligently step through templated code and data structures while displaying relevant information such as the parameter types
Can handle threaded applications and switch between different threads to step through or view the state of
Can handle attaching to an already-started process or reading a core dump, in addition to starting the program up in gdb
If such a program does not exist, then I'd like to hear about experiences people have had with programs that meet at least some of the bullet points.
Does anyone have any recommendations?
Edit:
Listing out the possibilities is great, and I'll take what I can get, but it would be even more helpful if you could include in your responses:
(a) Whether or not you've actually used this GUI and if so, what positive/negative feedback you have about it.
(b) If you know, which of the above-mentioned features are/aren't supported
Lists are easy to come by, sites like this are great because you can get an idea of people's personal experiences with applications.
|
You won't find anything overlaying GDB which can compete with the raw power of the Visual Studio debugger. It's just too powerful, and it's just too well integrated inside the IDE.
For a Linux alternative, try DDD if free software is your thing.
|
79,210 | 79,358 |
Best C++ IDE for *nix
|
What is the best C++ IDE for a *nix envirnoment? I have heard the C/C++ module of Eclipse is decent as well as Notepad++ but beyond these two I have no real idea. Any thoughts or comments?
|
On Ubuntu, some the IDEs that are available in the repositories are:
Kdevelop
Geany
Anjuta
There is also:
Eclipse (Recommended you don't install from repositories, due to issues with file/folder permissions)
Code::blocks
And of course, everyone's favourite text-based editors:
vi/vim
emacs
Its true that vim and emacs are very powerful tools, but the learning curve is very steep..
I really don't like Eclipse that much, I find it buggy and a bit too clunky.
I've started using Geany as a bare-bones but functional and usable IDE. It has a basic code-completion feature, and is a nice, clean [Gnome] interface.
Anjuta I tried for a day, didn't like it at all. I didn't find it as useful as Geany.
Kdevelop and code::blocks get a bunch of good reviews, but I haven't tried them. I use gnome, and I'm yet to see a KDE app that looks good in gnome (sorry, I'm sure its a great program).
If only bloodshed dev-c++ was released under linux. That is a fantastic (but windows-only) program. You could always run it under Wine ;)
To a degree, it comes down to personal preference. My advice is to investigate Kdevelop, Geany and code::blocks as a starting point.
|
79,356 | 79,859 |
What is best for desktop widgets (small footprint and pretty graphics)?
|
If I were to want to create a nice looking widget to stay running in the background with a small memory footprint, where would I start building the windows application. It's goal is to keep an updated list of items off of a web service. Similar to an RSS reader.
note: The data layer will be connecting through REST, which I already have a C# dll, that I assume will not affect the footprint too much.
Obviously i would like to use a nice WPF project, but the ~60,000k initial size is too big.
*C# Forms application is about ~20,000k
*C++ Forms ~16,000k
*CLR or MFC much smaller, under 5
Is there a way to strip down the WPF or Forms? and if im stuck using CLR or MFC what would be the easiest way to make it pretty. (my experience with MFC is making very award forms)
Update: Clarification The above sizes, are the memory being used as the process is ran, not the executable.
|
re:
Update: Clarification The above sizes,
are the memory being used as the
process is ran, not the executable.
Okay, when you run a tiny C# Win Forms app, the smallest amount of RAM that is reserved for it is around 2 meg, maybe 4 meg. This is just a working set that it creates. It's not actively using all of this memory, or anything like it. It just reserves that much space up front so it doesn't have to do long/slow/expensive requests for more memory later as needed.
Reserving a smaller size upfront is likely to be a false optimization.
(You can reduce the working set with a pinvoke call if it really matters. see pinvoke for 'set process working set size' )
|
79,745 | 79,817 |
How to determine which version of Direct3D is installed?
|
We have an application which needs to use Direct3D. Specifically, it needs at least DirectX 9.0c version 4.09.0000.0904. While this should be present on all newer XP machines it might not be installed on older XP machines. How can I programmatically (using C++) determine if it is installed? I want to be able to give an information message to the user that Direct3D will not be available.
|
Call DirectXSetupGetVersion: http://msdn.microsoft.com/en-us/library/microsoft.directx_sdk.directsetup.directxsetupgetversion
You'll need to include dsetup.h
Here's the sample code from the site:
DWORD dwVersion;
DWORD dwRevision;
if (DirectXSetupGetVersion(&dwVersion, &dwRevision))
{
printf("DirectX version is %d.%d.%d.%d\n",
HIWORD(dwVersion), LOWORD(dwVersion),
HIWORD(dwRevision), LOWORD(dwRevision));
}
|
80,341 | 80,402 |
Best OS App for Outbound SMTP Packet Capture?
|
Okay, so this probably sounds terribly nefarious, but I need such capabilities for my senior project. Essentially I'm tasked with writing something that will cut down outbound spam on a zombified pc through a system of packet interception and evaluation. We have a number of algorithms we'll use on the captured messages, but it's the actual capture -- full on interception rather than just sniffing -- that has me a bit stumped.
The app is being designed for windows, so I can't use IP tables. I could use the winpcap libraries, but I don't want to reinvent the wheel if I don't have to. Ettercap seemed a good option, but a test run on vista using the unofficial binaries resulted in nothing but crashes.
So, any suggestions?
Update: Great suggestions. Ended up scaling back the project a bit, but still received an A. I'm thinking Adam Mintz's answer is probably best, though we used WinPcap and Wireshark for the application.
|
Sounds like you need to write a Winsock LSP.
Once in the stack, a Layered Service Provider can intercept and modify inbound and outbound Internet traffic. It allows processing all the TCP/IP traffic taking place between the Internet and the applications that are accessing the Internet.
|
80,348 | 80,573 |
In C++, can you have a function that modifies a tuple of variable length?
|
In C++0x I would like to write a function like this:
template <typename... Types>
void fun(typename std::tuple<Types...> my_tuple) {
//Put things into the tuple
}
I first tried to use a for loop on int i and then do:
get<i>(my_tuple);
And then store some value in the result. However, get only works on constexpr.
If I could get the variables out of the tuple and pass them to a variadic templated function I could recurse through the arguments very easily, but I have no idea how to get the variables out of the tuple without get. Any ideas on how to do that? Or does anyone have another way of modifying this tuple?
|
Since the "i" in
get<i>(tup)
needs to be a compile-time constant, template instantiation is used to "iterate" (actually recurse) through the values. Boost tuples have the "length" and "element" meta-functions that can be helpful here -- I assume C++0x has these too.
|
80,452 | 81,070 |
Best technology for developing an app that runs on DESKTOP and in BROWSER?
|
Microsoft WPF? Adobe AIR/Flex? Adobe Flash? Curl programming language?
How does AJAX fit in?
Given a server written in C++ .NET.
|
The answer does depend really on what your application actually does and your platform requirements.
If its a regular web application like gmail and you want it to work on lots of browsers and platforms; then I'd recommend a combination of HTML, CSS and GWT as this means your application code is all Java, its very easy to refactor modularise and maintain, there's a ton of Java programmers out there and the IDEs for Java are awesome (IntelliJ or eclipse etc).
You can then use browser plugins like Siverlight or Flex if and when they make sense (e.g. like Google finance uses Flash for interactive graphs).
If your application is highly graphical like a Visio type of thing or needs to embed Microsoft Office or something; you might wanna look at Silverlight/Flex/AIR particularly if you can kinda dictate the browser versions and platforms for an internal application.
Though with client side there's no clear single answer (just look at the comments on this thread :) there are many options (Java Applets/Swing/JavaFX, Ajax, GWT, Air/Flex, Silverlight/.Net etc) which all have strengths and weaknesses. My recommendation for the communication between the client and your C++ server would be to expose your C++ application as a set of RESTful resources - then at any point in time you can easily write other kinds of clients in any language technology or framework.
|
80,518 | 80,566 |
What happens when the stylus "lifts" on a tablet PC?
|
I am working on a legacy project in VC++/Win32/MFC. Recently it became a requirement that the application work on a tablet pc, and this ushered in a host of new issues.
I have been able to work with, and around these issues, but am left with one wherein I could use some expert suggestions.
I have a particular bug that is induced by the "lift" of the stylus off of the active surface. Basically the mouse cursor disappears and then reappears when you "press" it back onto the screen.
It makes sense that this is unaccounted for in the application. you can't lift the cursor on a desktop pc. So what I am looking for is a good overview on what happens (in terms of windows messages, etc.) when the lift occurs. Does this translate to just focus changes and mouseover events? My bug seems to also involve cursor changes (may not be lift related though). Certainly the unexpected "lift" is breaking the state of the application's tool processing.
So the tangible questions are:
What happens when a stylus "lift" occurs? A press?
What API calls can be used to detect this? Does it just translate into standard messages with flags/values set?
Whats a good way to test/emulate this when your development pc is a desktop? Am I just flying blind here? (I only have periodic access to a tablet pc)
What represents correct behavior or best practice for tablet stylus awareness?
Thanks for your consideration,
ee
|
As a tablet user I can answer a few of your questions.
First:
You cannot very easily keep a "keyboard focus" on a window when the stylus has to trail out of the focused window to push a key on the virtual keyboard.
Most of the virtual keyboards I've used (The windows tablet input panel and one under ubuntu) allow the program they are typing in to keep "keyboard focus."
What happens when a stylus "lift" occurs? A press?
Under Windows, the pressure value drops, but outside of that, there is no event. (I don't know about linux.)
What API calls can be used to detect this? Does it just translate into standard messages with flags/values set?
As mentioned above, if you can get the pressure value, you can use that.
Whats a good way to test/emulate this when your development pc is a desktop? Am I just flying blind here? (I only have periodic access to a tablet pc)
When the stylus is placed down elsewhere, the global coordinates of the pointer change, so, you can emulate the sudden pointer move with anything that allows you to change the global pointer values. (The Robot class in Java makes this fairly easy.)
What represents correct behavior or best practice for tablet stylus awareness?
I'd recommend you read what Microsoft has to say, the MSDN website has a number of excellent articles. (http://msdn.microsoft.com/en-us/library/ms704849(VS.85).aspx)
I'll point out that the size of the buttons on your applications makes a HUGE difference.
Hope this was of help.
|
80,619 | 80,651 |
'Helper' functions in C++
|
While refactoring some old code I have stripped out a number of public methods that should actually of been statics as they a) don't operate on any member data or call any other member functions and b) because they might prove useful elsewhere.
This led me to think about the best way to group 'helper' functions together. The Java/C# way would be to use a class of static functions with a private constructor, e.g.:
class Helper
{
private:
Helper() { }
public:
static int HelperFunc1();
static int HelperFunc2();
};
However, being C++ you could also use a namespace:
namespace Helper
{
int HelperFunc1();
int HelperFunc2();
}
In most cases I think I would prefer the namespace approach but I wanted to know what the pros and cons of each approach are. If used the class approach for example, would there be any overheads?
|
Overhead is not an issue, namespaces have some advantages though
You can reopen a namespace in another header, grouping things more logically while
keeping compile dependencies low
You can use namespace aliasing to your advantage
(debug/release, platform specific helpers, ....)
e.g. I've done stuff like
namespace LittleEndianHelper {
void Function();
}
namespace BigEndianHelper {
void Function();
}
#if powerpc
namespace Helper = BigEndianHelper;
#elif intel
namespace Helper = LittleEndianHelper;
#endif
|
80,691 | 81,827 |
Orthogonal variables code duplication problem
|
I've started refactoring some legacy code recently and came across two functions for drawing a coordinate grid, the problem is that these functions differ only in orthogonal variables they treat, something like that
void DrawScaleX(HDC dc, int step, int x0, int x1, int y0, int y1)
{
for(int x = x0; x < x1; x += step)
{
MoveToEx(dc, x, y0, NULL);
LineTo(dc, x, y1);
}
}
void DrawScaleY(HDC dc, int step, int x0, int x1, int y0, int y1)
{
for(int y = y0; y < y1; y += step)
{
MoveToEx(dc, x0, y, NULL);
LineTo(dc, x1, y);
}
}
So if I decide to add some fancy stuff, like antialiasing or merely change drawing pencil or whatever I'll have to put the same code in both of them and it's code duplication and it's bad we all know why.
My question is how would you rewrite these two functions into a single one to avoid this problem?
|
Drawing a line is simply joining two points, and drawing a scaling incrementing (x0,y0) and(x1,y1) in a particular direction, through X, and/or through Y.
This boils down to, in the scale case, which direction(s) stepping occurs (maybe both directions for fun).
template< int XIncrement, YIncrement >
struct DrawScale
{
void operator()(HDC dc, int step, int x0, int x1, int y0, int y1)
{
const int deltaX = XIncrement*step;
const int deltaY = YIncrement*step;
const int ymax = y1;
const int xmax = x1;
while( x0 < xmax && y0 < ymax )
{
MoveToEx(dc, x0, y0, NULL);
LineTo(dc, x1, y1);
x0 += deltaX;
x1 += deltaX;
y0 += deltaY;
y1 += deltaY;
}
}
};
typedef DrawScale< 1, 0 > DrawScaleX;
typedef DrawScale< 0, 1 > DrawScaleY;
The template will do its job: at compile time the compiler will remove all the null statements i.e. deltaX or deltaY is 0 regarding which function is called and half of the code goes away in each functor.
You can add you anti-alias, pencil stuff inside this uniq function and get the code properly generated generated by the compiler.
This is cut and paste on steroids ;-)
-- ppi
|
80,831 | 90,972 |
How to find out the distinguished name of the information store to feed to IExchangeManageStore::GetMailboxTable?
|
There is a Microsoft knowledge base article with sample code to open all mailboxes in a given information store. It works so far (requires a bit of copy & pasting on compilers newer than VC++ 6.0).
At one point it calls IExchangeManageStore::GetMailboxTable with the distinguished name of the information store. For the Exchange 2007 Trial Virtual Server image it has to look like this:
"/o=Litware Inc/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Configuration/cn=servers/cn=DC1".
Using OutlookSpy and clicking on IMsgStore and IExchangeManageStore reveals the desired string next to "Server DN:".
I want to avoid forcing the user to put this into a config file. So if OutlookSpy can do it, how can my application find out the distinguished name of the information store where the currently open mailbox is on?
|
Thinking there must be a pure MAPI solution, I believe I've figured out how OutlookSpy does it.
The following code snippet, inserted after
printf("Created MAPI session\n");
in the example from KB194627, will show the Server DN.
LPPROFSECT lpProfSect;
hr = lpSess->OpenProfileSection((LPMAPIUID)pbGlobalProfileSectionGuid, NULL, 0, &lpProfSect);
if(SUCCEEDED(hr))
{
LPSPropValue lpPropValue;
hr = HrGetOneProp(lpProfSect, PR_PROFILE_HOME_SERVER_DN, &lpPropValue);
if(SUCCEEDED(hr))
{
printf("Server DN: %s\n", lpPropValue->Value.lpszA);
MAPIFreeBuffer(lpPropValue);
}
lpProfSect->Release();
}
Update:
There is the function HrGetServerDN in the EDK 5.5 source code, it extracts the Server DN from a given session's PR_EMS_AB_HOME_MTA. I'll try it if the other way turns out to be unreliable.
|
82,415 | 82,526 |
Prefetch instructions on ARM
|
Newer ARM processors include the PLD and PLI instructions.
I'm writing tight inner loops (in C++) which have a non-sequential memory access pattern, but a pattern that naturally my code fully understands. I would anticipate a substantial speedup if I could prefetch the next location whilst processing the current memory location, and I would expect this to be quick-enough to try out to be worth the experiment!
I'm using new expensive compilers from ARM, and it doesn't seem to be including PLD instructions anywhere, let alone in this particular loop that I care about.
How can I include explicit prefetch instructions in my C++ code?
|
There should be some Compiler-specific Features. There is no standard way to do it for C/C++. Check out you compiler Compiler Reference Guide. For RealView Compiler see this or this.
|
82,495 | 84,292 |
Has anyone tried transactional memory for C++?
|
I was checking out Intel's "whatif" site and their Transactional Memory compiler (each thread has to make atomic commits or rollback the system's memory, like a Database would).
It seems like a promising way to replace locks and mutexes but I can't find many testimonials. Does anyone here have any input?
|
I have not used Intel's compiler, however, Herb Sutter had some interesting comments on it...
From Sutter Speaks: The Future of Concurrency
Do you see a lot of interest in and usage of transactional memory, or is the concept too difficult for most developers to grasp?
It's not yet possible to answer who's using it because it hasn't been brought to market yet. Intel has a software transactional memory compiler prototype. But if the question is "Is it too hard for developers to use?" the answer is that I certainly hope not. The whole point is it's way easier than locks. It is the only major thing on the research horizon that holds out hope of greatly reducing our use of locks. It will never replace locks completely, but it's our only big hope to replacing them partially.
There are some limitations. In particular, some I/O is inherently not transactional—you can't take an atomic block that prompts the user for his name and read the name from the console, and just automatically abort and retry the block if it conflicts with another transaction; the user can tell the difference if you prompt him twice. Transactional memory is great for stuff that is only touching memory, though.
Every major hardware and software vendor I know of has multiple transactional memory tools in R&D. There are conferences and academic papers on theoretical answers to basic questions. We're not at the Model T stage yet where we can ship it out. You'll probably see early, limited prototypes where you can't do unbounded transactional memory—where you can only read and write, say, 100 memory locations. That's still very useful for enabling more lock-free algorithms, though.
|
82,550 | 83,616 |
Boost serialization: specifying a template class version
|
I have a template class that I serialize (call it C), for which I want to specify a version for boost serialization. As BOOST_CLASS_VERSION does not work for template classes. I tried this:
namespace boost {
namespace serialization {
template< typename T, typename U >
struct version< C<T,U> >
{
typedef mpl::int_<1> type;
typedef mpl::integral_c_tag tag;
BOOST_STATIC_CONSTANT(unsigned int, value = version::type::value);
};
}
}
but it does not compile. Under VC8, a subsequent call to BOOST_CLASS_VERSION gives this error:
error C2913: explicit specialization; 'boost::serialization::version' is not a specialization of a class template
What is the correct way to do it?
|
#include <boost/serialization/version.hpp>
:-)
|
83,439 | 83,538 |
Remove spaces from std::string in C++
|
What is the preferred way to remove spaces from a string in C++? I could loop through all the characters and build a new string, but is there a better way?
|
The best thing to do is to use the algorithm remove_if and isspace:
remove_if(str.begin(), str.end(), isspace);
Now the algorithm itself can't change the container(only modify the values), so it actually shuffles the values around and returns a pointer to where the end now should be. So we have to call string::erase to actually modify the length of the container:
str.erase(remove_if(str.begin(), str.end(), isspace), str.end());
We should also note that remove_if will make at most one copy of the data. Here is a sample implementation:
template<typename T, typename P>
T remove_if(T beg, T end, P pred)
{
T dest = beg;
for (T itr = beg;itr != end; ++itr)
if (!pred(*itr))
*(dest++) = *itr;
return dest;
}
|
83,640 | 83,705 |
C++ does begin/end/rbegin/rend execute in constant time for std::set, std::map, etc?
|
For data types such as std::set and std::map where lookup occurs in logarithmic time, is the implementation required to maintain the begin and end iterators? Does accessing begin and end imply a lookup that could occur in logarithmic time?
I have always assumed that begin and end always occur in constant time, however I can't find any confirmation of this in Josuttis. Now that I'm working on something where I need to be anal about performance, I want to make sure to cover my bases.
Thanks
|
They happen in constant time. I'm looking at page 466 of the ISO/IEC 14882:2003 standard:
Table 65 - Container Requiments
a.begin(); (constant complexity)
a.end(); (constant complexity)
Table 66 - Reversible Container Requirements
a.rbegin(); (constant complexity)
a.rend(); (constant complexity)
|
84,064 | 85,102 |
SQLBindParameter to prepare for SQLPutData using C++ and SQL Native Client
|
I'm trying to use SQLBindParameter to prepare my driver for input via SQLPutData. The field in the database is a TEXT field. My function is crafted based on MS's example here:
http://msdn.microsoft.com/en-us/library/ms713824(VS.85).aspx.
I've setup the environment, made the connection, and prepared my statement successfully but when I call SQLBindParam (using code below) it consistently fails reporting: [Microsoft][SQL Native Client]Invalid precision value
int col_num = 1;
SQLINTEGER length = very_long_string.length( );
retcode = SQLBindParameter( StatementHandle,
col_num,
SQL_PARAM_INPUT,
SQL_C_BINARY,
SQL_LONGVARBINARY,
NULL,
NULL,
(SQLPOINTER) col_num,
NULL,
&length );
The above relies on the driver in use returning "N" for the SQL_NEED_LONG_DATA_LEN information type in SQLGetInfo. My driver returns "Y". How do I bind so that I can use SQLPutData?
|
you're passing NULL as the buffer length, this is an in/out param that shoudl be the size of the col_num parameter. Also, you should pass a value for the ColumnSize or DecimalDigits parameters.
http://msdn.microsoft.com/en-us/library/ms710963(VS.85).aspx
|
84,269 | 254,883 |
Using Component Object Model (COM) on non-Microsoft platforms
|
I'm regularly running into similar situations :
I have a bunch of COM .DLLs (no IDL files) which I need to use and invoke to be able to access some foreign (non-open, non-documented) data format.
Microsoft's Visual Studio platform has very nice capabilities to import such COM DLLs and use them in my project (Visual C++'s #import directive, or picking and adding them using Visual Basic .NET's dialogs) - and that's the vendors recommended way to use them.
I would be interested into finding a way to use those DLLs on non-microsoft development platforms. Namely, using these COM classes in C++ project compiled with MinGW or Cygwin, or even Wine's GCC port to linux (compiles C++ targeting Win32 into binary running natively on Linux).
I have got some limited success using this driver, but this isn't successful in 100% of situations (I can't use COM objects returned by some methods).
Has someone had success in similar situations ?
|
Answering myself but I managed to find the perfect library for OLE/COM calling in non-Microsoft compilers : disphelper.
(it's available from sourceforge.net under a permissive BSD license).
It works both in C and C++ (and thus any other language with C bindings as well). It uses a printf/scanf-like format string syntax.
(You pass whatever you want as long as you specify it in the format string, unlike XYDispDriver which requires the arguments to exactly match whatever is specified in the type library).
I modified it a little bit to get it also compile under Linux with WineGCC (to produce native Linux elf out of Win32 code), and to handle "by ref" calls automatically (stock disthelper requires the programmer to setup his/her own VARIANT).
My patched version and patches are available as a fork on github:
https://github.com/DrYak/disphelper
And here are my patches :
patch for single source
patch for split source
|
84,427 | 84,562 |
Is it legal to pass a newly constructed object by reference to a function?
|
Specifically, is the following legal C++?
class A{};
void foo(A*);
void bar(const A&);
int main(void)
{
foo(&A()); // 1
bar(A()); // 2
}
It appears to work correctly, but that doesn't mean it's necessarily legal. Is it?
Edit - changed A& to const A&
|
1: Taking the address of a temporary is not allowed. Visual C++ allows it as a language extension (language extensions are on by default).
2: This is perfectly legal.
|
84,817 | 85,452 |
Super Robust as chrome c++ and portable - tips - help - comments
|
We are producing a portable code (win+macOs) and we are looking at how to make the code more rubust as it crashes every so often... (overflows or bad initializations usually) :-(
I was reading that Google Chrome uses a process for every tab so if something goes wrong then the program does not crash compleatelly, only that tab. I think that is quite neat, so i might give it a go!
So i was wondering if someone has some tips, help, reading list, comment, or something that can help me build more rubust c++ code (portable is always better).
In the same topic i was also wondering if there is a portable library for processes (like boost)?
Well many Thanks.
|
I've developed on numerous multi-platform C++ apps (the largest being 1.5M lines of code and running on 7 platforms -- AIX, HP-UX PA-RISC, HP-UX Itanium, Solaris, Linux, Windows, OS X). You actually have two entirely different issues in your post.
Instability. Your code is not stable. Fix it.
Use unit tests to find logic problems before they kill you.
Use debuggers to find out what's causing the crashes if it's not obvious.
Use boost and similar libraries. In particular, the pointer types will help you avoid memory leaks.
Cross-platform coding.
Again, use libraries that are designed for this when possible. Particularly for any GUI bits.
Use standards (e.g. ANSI vs gcc/MSVC, POSIX threads vs Unix-specific thread models, etc) as much as possible, even if it requires a bit more work. Minimizing your platform specific code means less overall work, and fewer APIs to learn.
Isolate, isolate, isolate. Avoid in-line #ifdefs for different platforms as much as possible. Instead, stick platform specific code into its own header/source/class and use your build system and #includes to get the right code. This helps keep the code clean and readable.
Use the C99 integer types if at all possible instead of "long", "int", "short", etc -- otherwise it will bite you when you move from a 32-bit platform to a 64-bit one and longs suddenly change from 4 bytes to 8 bytes. And if that's ever written to the network/disk/etc then you'll run into incompatibility between platforms.
Personally, I'd stabilize the code first (without adding any more features) and then deal with the cross-platform issues, but that's up to you. Note that Visual Studio has an excellent debugger (the code base mentioned above was ported to Windows just for that reason).
|
85,122 | 85,143 |
How to make thread sleep less than a millisecond on Windows
|
On Windows I have a problem I never encountered on Unix. That is how to get a thread to sleep for less than one millisecond. On Unix you typically have a number of choices (sleep, usleep and nanosleep) to fit your needs. On Windows, however, there is only Sleep with millisecond granularity.
On Unix, I can use the use the select system call to create a microsecond sleep which is pretty straightforward:
int usleep(long usec)
{
struct timeval tv;
tv.tv_sec = usec/1000000L;
tv.tv_usec = usec%1000000L;
return select(0, 0, 0, 0, &tv);
}
How can I achieve the same on Windows?
|
On Windows the use of select forces you to include the Winsock library which has to be initialized like this in your application:
WORD wVersionRequested = MAKEWORD(1,0);
WSADATA wsaData;
WSAStartup(wVersionRequested, &wsaData);
And then the select won't allow you to be called without any socket so you have to do a little more to create a microsleep method:
int usleep(long usec)
{
struct timeval tv;
fd_set dummy;
SOCKET s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP);
FD_ZERO(&dummy);
FD_SET(s, &dummy);
tv.tv_sec = usec/1000000L;
tv.tv_usec = usec%1000000L;
return select(0, 0, 0, &dummy, &tv);
}
All these created usleep methods return zero when successful and non-zero for errors.
|
86,046 | 86,146 |
Best way to start a thread as a member of a C++ class?
|
I'm wondering the best way to start a pthread that is a member of a C++ class? My own approach follows as an answer...
|
I usually use a static member function of the class, and use a pointer to the class as the void * parameter. That function can then either perform thread processing, or call another non-static member function with the class reference. That function can then reference all class members without awkward syntax.
|
86,219 | 87,159 |
Interfacing with telephony systems from *nix
|
Does anyone know of any 'standard' way to interface with a telephony system (think Cisco CCM) from a C/C++ app in *nix? I have used MS TAPI in the past but this is Windows only and don't want to go the jTAPI (Java) route, which seems to be the only option on the face of it.
I want to monitor the phone system for logging purposes (so I know when users have made calls, received calls, etc.). TAPI is good at this sort of thing but I can't be the first person who wants to do something similar without having a Windows server.
Note that I need to integrate with existing PABX systems - notably Cisco CCM and Nortel BCM.
|
I have experience with two telephony standards TAPI, and CSTA, as far as I know there is no such agreement between vendors (e.g. Cisco, Nortel, NEC) regarding THE standard API.
I would recommend looking at the availability of SMDR (Station Messaging Detail Recording) on the PBX platforms you are targeting, assuming that no call/device control is required. This will allow you to access the PBX activity as a text stream and you can parse the data for further manipulations to suit your purpose.
Most likely the format between the PBX vendors will be different but hopefully this could be abstracted away so that the core application functionality is re-usable.
This is likely to be a more portable option, again assuming no call/device control is required, as you are not relying on the vendor providing CTI connectivity on your platform of choice.
|
86,474 | 86,522 |
Firing COM events in C++ - Synchronous or asynchronous?
|
I have an ActiveX control written using the MS ATL library and I am firing events via pDispatch->Invoke(..., DISPATCH_METHOD). The control will be used by a .NET client and my question is this - is the firing of the event a synchronous or asynchronous call? My concern is that, if synchronous, the application that handles the event could cause performance issues unless it returns immediately.
|
It is synchronous from the point of view of the component generating the event. The control's thread of execution will call out into the receivers code and things are out of its control at that point.
Clients receiving the events must make sure they return quickly. If they need to do some significant amount of work then they should schedule this asynchronously. For example by posting a windows message, or using a separate thread.
|
86,582 | 92,193 |
Singleton: How should it be used
|
Edit:
From another question I provided an answer that has links to a lot of questions/answers about singletons: More info about singletons here:
So I have read the thread Singletons: good design or a crutch?
And the argument still rages.
I see Singletons as a Design Pattern (good and bad).
The problem with Singleton is not the Pattern but rather the users (sorry everybody). Everybody and their father thinks they can implement one correctly (and from the many interviews I have done, most people can't). Also because everybody thinks they can implement a correct Singleton they abuse the Pattern and use it in situations that are not appropriate (replacing global variables with Singletons!).
So the main questions that need to be answered are:
When should you use a Singleton
How do you implement a Singleton correctly
My hope for this article is that we can collect together in a single place (rather than having to google and search multiple sites) an authoritative source of when (and then how) to use a Singleton correctly. Also appropriate would be a list of Anti-Usages and common bad implementations explaining why they fail to work and for good implementations their weaknesses.
So get the ball rolling:
I will hold my hand up and say this is what I use but probably has problems.
I like "Scott Myers" handling of the subject in his books "Effective C++"
Good Situations to use Singletons (not many):
Logging frameworks
Thread recycling pools
/*
* C++ Singleton
* Limitation: Single Threaded Design
* See: http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf
* For problems associated with locking in multi threaded applications
*
* Limitation:
* If you use this Singleton (A) within a destructor of another Singleton (B)
* This Singleton (A) must be fully constructed before the constructor of (B)
* is called.
*/
class MySingleton
{
private:
// Private Constructor
MySingleton();
// Stop the compiler generating methods of copy the object
MySingleton(MySingleton const& copy); // Not Implemented
MySingleton& operator=(MySingleton const& copy); // Not Implemented
public:
static MySingleton& getInstance()
{
// The only instance
// Guaranteed to be lazy initialized
// Guaranteed that it will be destroyed correctly
static MySingleton instance;
return instance;
}
};
OK. Lets get some criticism and other implementations together.
:-)
|
Answer:
Use a Singleton if:
You need to have one and only one object of a type in system
Do not use a Singleton if:
You want to save memory
You want to try something new
You want to show off how much you know
Because everyone else is doing it (See cargo cult programmer in wikipedia)
In user interface widgets
It is supposed to be a cache
In strings
In Sessions
I can go all day long
How to create the best singleton:
The smaller, the better. I am a minimalist
Make sure it is thread safe
Make sure it is never null
Make sure it is created only once
Lazy or system initialization? Up to your requirements
Sometimes the OS or the JVM creates singletons for you (e.g. in Java every class definition is a singleton)
Provide a destructor or somehow figure out how to dispose resources
Use little memory
|
87,220 | 4,506,050 |
How does gcc implement stack unrolling for C++ exceptions on linux?
|
How does gcc implement stack unrolling for C++ exceptions on linux? In particular, how does it know which destructors to call when unrolling a frame (i.e., what kind of information is stored and where is it stored)?
|
See section 6.2 of the x86_64 ABI. This details the interface but not a lot of the underlying data. This is also independent of C++ and could conceivably be used for other purposes as well.
There are primarily two sections of the ELF binary as emitted by gcc which are of interest for exception handling. They are .eh_frame and .gcc_except_table.
.eh_frame follows the DWARF format (the debugging format that primarily comes into play when you're using gdb). It has exactly the same format as the .debug_frame section emitted when compiling with -g. Essentially, it contains the information necessary to pop back to the state of the machine registers and the stack at any point higher up the call stack. See the Dwarf Standard at dwarfstd.org for more information on this.
.gcc_except_table contains information about the exception handling "landing pads" the locations of handlers. This is necessary so as to know when to stop unwinding. Unfortunately this section is not well documented. The only snippets of information I have been able to glean come from the gcc mailing list. See particularly this post
The remaining piece of information is then what actual code interprets the information found in these data sections. The relevant code lives in libstdc++ and libgcc. I cannot remember at the moment which pieces live in which. The interpreter for the DWARF call frame information can be found in the gcc source code in the file gcc/unwind-dw.c
|
87,372 | 87,846 |
Check if a class has a member function of a given signature
|
I'm asking for a template trick to detect if a class has a specific member function of a given signature.
The problem is similar to the one cited here
http://www.gotw.ca/gotw/071.htm
but not the same: in the item of Sutter's book he answered to the question that a class C MUST PROVIDE a member function with a particular signature, else the program won't compile. In my problem I need to do something if a class has that function, else do "something else".
A similar problem was faced by boost::serialization but I don't like the solution they adopted: a template function that invokes by default a free function (that you have to define) with a particular signature unless you define a particular member function (in their case "serialize" that takes 2 parameters of a given type) with a particular signature, else a compile error will happens. That is to implement both intrusive and non-intrusive serialization.
I don't like that solution for two reasons:
To be non intrusive you must override the global "serialize" function that is in boost::serialization namespace, so you have IN YOUR CLIENT CODE to open namespace boost and namespace serialization!
The stack to resolve that
mess was 10 to 12 function invocations.
I need to define a custom behavior for classes that has not that member function, and my entities are inside different namespaces (and I don't want to override a global function defined in one namespace while I'm in another one)
Can you give me a hint to solve this puzzle?
|
I'm not sure if I understand you correctly, but you may exploit SFINAE to detect function presence at compile-time. Example from my code (tests if class has member function size_t used_memory() const).
template<typename T>
struct HasUsedMemoryMethod
{
template<typename U, size_t (U::*)() const> struct SFINAE {};
template<typename U> static char Test(SFINAE<U, &U::used_memory>*);
template<typename U> static int Test(...);
static const bool Has = sizeof(Test<T>(0)) == sizeof(char);
};
template<typename TMap>
void ReportMemUsage(const TMap& m, std::true_type)
{
// We may call used_memory() on m here.
}
template<typename TMap>
void ReportMemUsage(const TMap&, std::false_type)
{
}
template<typename TMap>
void ReportMemUsage(const TMap& m)
{
ReportMemUsage(m,
std::integral_constant<bool, HasUsedMemoryMethod<TMap>::Has>());
}
|
87,405 | 87,460 |
Different versions of C++ libraries
|
After compiling a simple C++ project using Visual Studio 2008 on vista, everything runs fine on the original vista machine and other vista computers. However, moving it over to an XP box results in an error message: "The application failed to start because the application configuration is incorrect".
What do I have to do so my compiled EXE works on XP and Vista? I had this same problem a few months ago, and just fiddling with some settings on the project fixed it, but I don't remember which ones I changed.
|
You need to install the Visual Studios 2008 runtime on the target computer:
http://www.microsoft.com/downloads/details.aspx?FamilyID=9b2da534-3e03-4391-8a4d-074b9f2bc1bf&displaylang=en
Alternatively, you could also link the run time statically, in the project properties window go to:
c++ -> Code Generation -> Runtime
Library and select "multi-threaded
/MT"
|
87,610 | 87,882 |
Automated integration testing a C++ app with a database
|
I am introducing automated integration testing to a mature application that until now has only been manually tested.
The app is Windows based and talks to a MySQL database.
What is the best way (including details of any tools recommended) to keep tests independent of each other in terms of the database transactions that will occur?
(Modifications to the app source for this particular purpose are not an option.)
|
How are you verifying the results?
If you need to query the DB (and it sounds like you probably do) for results then I agree with Kris K, except I would endeavor to rebuild the DB after every test case, not just every suite.
This helps avoid dangerous interacting tests
As for tools, I would recommend CppUnit. You aren't really doing unit tests, but it shouldn't matter as the xUnit framework should give you the set up and teardown framework you'll need to automatically set up your test fixture
Obviously this can result in slow-running tests, depending on your database size, population etc. You may be able to attach/detach databases rather than dropping/rebuilding.
If you're interested in further research, check out XUnit Test Patterns. It's a fine book and a good website for this kind of thing.
And thanks for automating :)
Nick
|
87,689 | 92,462 |
Testing running condition of a Windows app
|
I have several applications that are part of a suite of tools that various developers at our studio use. these applications are mainly command line apps that open a DOS cmd shell. These apps in turn start up a GUI application that tracks output and status (via sockets) of these command line apps.
The command line apps can be started with the user is logged in, when their workstation is locked (they fire off a batch file and then immediately lock their workstaion), and when they are logged out (via a scheduled task). The problems that I have are with the last two cases.
If any of these apps fire off when the user is locked or logged out, these command will spawn the GUI windows which tracks the output/status. That's fine, but say the user has their workstation locked -- when they unlock their workstation, the GUI isn't visible. It's running the task list, but it's not visible. The next time these users run some of our command line apps, the GUI doesn't get launched (because it's already running), but because it's not visible on the desktop, users don't see any output.
What I'm looking for is a way to tell from my command line apps if they are running behind a locked workstation or when a user is logged out (via scheduled task) -- basically are they running without a user's desktop visible. If I can tell that, then I can simply not start up our GUI and can prevent a lot of problem.
These apps that I need to test are C/C++ Windows applications.
I hope that this make sense.
|
I found the programmatic answer that I was looking for. It has to do with stations. Apparently anything running on the desktop will run on a station with a particular name. Anything that isn't on the desktop (i.e. a process started by the task manager when logged off or on a locked workstation) will get started with a different station name. Example code:
HWINSTA dHandle = GetProcessWindowStation();
if ( GetUserObjectInformation(dHandle, UOI_NAME, nameBuffer, bufferLen, &lenNeeded) ) {
if ( stricmp(nameBuffer, "winsta0") ) {
// when we get here, we are not running on the real desktop
return false;
}
}
If you get inside the 'if' statement, then your process is not on the desktop, but running "somewhere else". I looked at the namebuffer value when not running from the desktop and the names don't mean much, but they are not WinSta0.
Link to the docs here.
|
87,794 | 92,750 |
C++ unit testing framework
|
I use the Boost Test framework for my C++ code but there are two problems with it that are probably common to all C++ test frameworks:
There is no way to create automatic test stubs (by extracting public functions from selected classes for example).
You cannot run a single test - you have to run the entire 'suite' of tests (unless you create lots of different test projects I guess).
Does anyone know of a better testing framework or am I forever to be jealous of the test tools available to Java/.NET developers?
|
I just responded to a very similar question. I ended up using Noel Llopis' UnitTest++. I liked it more than boost::test because it didn't insist on implementing the main program of the test harness with a macro - it can plug into whatever executable you create. It does suffer from the same encumbrance of boost::test in that it requires a library to be linked in. I've used CxxTest, and it does come closer than anything else in C++-land to automatically generating tests (though it requires Perl to be part of your build system to do this). C++ just does not provide the reflection hooks that the .NET languages and Java do. The MsTest tools in Visual Studio Team System - Developer's Edition will auto-generate test stubs of unmanaged C++, but the methods have to be exported from a DLL to do this, so it does not work with static libraries. Other test frameworks in the .NET world may have this ability too, but I'm not familiar with any of those. So right now we use UnitTest++ for unmanaged C++ and I'm currently deciding between MsTest and NUnit for the managed libraries.
|
87,831 | 87,948 |
How do I use my own compiler with Nant?
|
Nant seems very compiler-centric - which is guess is because it's considered a .NET development system. But I know it can be done! I've seen it. The platform we're building on has its own compiler and doesn't use 'cl.exe' for c++. We're building a C++ app on a different platform and would like to override with our own compiler. Can anyone point me at a way to do that or at least how to set up a target of my own that will use our target platform's compiler?
|
Here is one I did for Delphi. Each 'arg' is a separate param with a value defined elsewhere. The target is called with the params set up before calling it.
<target name="build.application">
<exec program="dcc32" basedir="${Delphi.Bin}" workingdir="${Application.Folder}" verbose="true">
<arg value="${Application.Compiler.Directive}" />
<arg value="-Q" />
<arg value="/B" />
<arg value="/E${Application.Output.Folder}" />
<arg value="/U${Application.Lib.Folder};${Application.Search.Folder}" />
<arg value="${Application.Folder}\${Delphi.Project}" />
</exec>
</target>
|
87,932 | 88,215 |
Attribute & Reflection libraries for C++?
|
Most mature C++ projects seem to have an own reflection and attribute system, i.e for defining attributes which can be accessed by string and are automatically serializable. At least many C++ projects I participated in seemed to reinvent the wheel.
Do you know any good open source libraries for C++ which support reflection and attribute containers, specifically:
Defining RTTI and attributes via macros
Accessing RTTI and attributes via code
Automatic serialisation of attributes
Listening to attribute modifications (e.g. OnValueChanged)
|
You could have a look at the two tools below. I've never used either of them, so I can't tell you how (im)practical they are.
XRTTI:
Xrtti is a tool and accompanying C++ library which extends the standard runtime type system of C++ to provide a much richer set of reflection information about classes and methods to manipulate these classes and their members.
OpenC++:
OpenC++ is C++ frontend library (lexer+parser+DOM/MOP) and source-to-source translator. OpenC++ enables development of C++ language tools, extensions, domain specific compiler optimizations and runtime metaobject protocols.
|
88,573 | 88,905 |
Should I use an exception specifier in C++?
|
In C++, you can specify that a function may or may not throw an exception by using an exception specifier. For example:
void foo() throw(); // guaranteed not to throw an exception
void bar() throw(int); // may throw an exception of type int
void baz() throw(...); // may throw an exception of some unspecified type
I'm doubtful about actually using them because of the following:
The compiler doesn't really enforce exception specifiers in any rigorous way, so the benefits are not great. Ideally, you would like to get a compile error.
If a function violates an exception specifier, I think the standard behaviour is to terminate the program.
In VS.Net, it treats throw(X) as throw(...), so adherence to the standard is not strong.
Do you think exception specifiers should be used?
Please answer with "yes" or "no" and provide some reasons to justify your answer.
|
No.
Here are several examples why:
Template code is impossible to write with exception specifications,
template<class T>
void f( T k )
{
T x( k );
x.x();
}
The copies might throw, the parameter passing might throw, and x() might throw some unknown exception.
Exception-specifications tend to prohibit extensibility.
virtual void open() throw( FileNotFound );
might evolve into
virtual void open() throw( FileNotFound, SocketNotReady, InterprocessObjectNotImplemented, HardwareUnresponsive );
You could really write that as
throw( ... )
The first is not extensible, the second is overambitious and the third is really what you mean, when you write virtual functions.
Legacy code
When you write code which relies on another library, you don't really know what it might do when something goes horribly wrong.
int lib_f();
void g() throw( k_too_small_exception )
{
int k = lib_f();
if( k < 0 ) throw k_too_small_exception();
}
g will terminate, when lib_f() throws. This is (in most cases) not what you really want. std::terminate() should never be called. It is always better to let the application crash with an unhandled exception, from which you can retrieve a stack-trace, than to silently/violently die.
Write code that returns common errors and throws on exceptional occasions.
Error e = open( "bla.txt" );
if( e == FileNotFound )
MessageUser( "File bla.txt not found" );
if( e == AccessDenied )
MessageUser( "Failed to open bla.txt, because we don't have read rights ..." );
if( e != Success )
MessageUser( "Failed due to some other error, error code = " + itoa( e ) );
try
{
std::vector<TObj> k( 1000 );
// ...
}
catch( const bad_alloc& b )
{
MessageUser( "out of memory, exiting process" );
throw;
}
Nevertheless, when your library just throws your own exceptions, you can use exception specifications to state your intent.
|
88,957 | 88,960 |
What does {0} mean when initializing an object?
|
When {0} is used to initialize an object, what does it mean? I can't find any references to {0} anywhere, and because of the curly braces Google searches are not helpful.
Example code:
SHELLEXECUTEINFO sexi = {0}; // what does this do?
sexi.cbSize = sizeof(SHELLEXECUTEINFO);
sexi.hwnd = NULL;
sexi.fMask = SEE_MASK_NOCLOSEPROCESS;
sexi.lpFile = lpFile.c_str();
sexi.lpParameters = args;
sexi.nShow = nShow;
if(ShellExecuteEx(&sexi))
{
DWORD wait = WaitForSingleObject(sexi.hProcess, INFINITE);
if(wait == WAIT_OBJECT_0)
GetExitCodeProcess(sexi.hProcess, &returnCode);
}
Without it, the above code will crash on runtime.
|
What's happening here is called aggregate initialization. Here is the (abbreviated) definition of an aggregate from section 8.5.1 of the ISO spec:
An aggregate is an array or a class with no user-declared constructors, no private or protected non-static data members, no base classes, and no virtual functions.
Now, using {0} to initialize an aggregate like this is basically a trick to 0 the entire thing. This is because when using aggregate initialization you don't have to specify all the members and the spec requires that all unspecified members be default initialized, which means set to 0 for simple types.
Here is the relevant quote from the spec:
If there are fewer initializers in the list than there are members in the
aggregate, then each member not
explicitly initialized shall be
default-initialized.
Example:
struct S { int a; char* b; int c; };
S ss = { 1, "asdf" };
initializes ss.a with 1, ss.b with
"asdf", and ss.c with the value of an
expression of the form int(), that is,
0.
You can find the complete spec on this topic here
|
88,991 | 90,563 |
Produce conditional compile time error in Java
|
I do not mean the compile errors because I made a syntax mistake or whatever. In C++ we can create compile time errors based on conditions as in the following example:
template<int> struct CompileTimeError;
template<> struct CompileTimeError<true> {};
#define STATIC_CHECK(expr, msg) { CompileTimeError<((expr) != 0)> ERROR_##msg; (void)ERROR_##msg; }
int main(int argc, char* argv[])
{
STATIC_CHECK(false, Compile_Time_Failure);
return 0;
}
In VS 2005 this will output:
------ Build started: Project: Test, Configuration: Debug Win32 ------
Compiling...
Test.cpp
f:\temp\test\test\test.cpp(17) : error C2079: 'ERROR_Compile_Time_Failure' uses undefined struct 'CompileTimeError<__formal>'
with
[
__formal=0
]
Build log was saved at "file://f:\temp\Test\Test\Debug\BuildLog.htm"
Test - 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Is there any way to achieve this in Java?
|
There is no way to do this in Java, not in the same way it works for you in C++.
You could perhaps use annotations, and run apt before or after compilation to check your annotations.
For example:
@MyStaticCheck(false, "Compile Time Error, kind-of")
public static void main(String[] args) {
return;
}
And then write your own AnnotationProcessorFactory that looked for @MyStaticCheck annotations, and does something with the arguments.
Note: I haven't played too much with apt, but the documentation makes it looks like this is very do-able.
|
89,275 | 89,284 |
Best C++ IDE or Editor for Windows
|
What is the best C++ IDE or editor for using on Windows? I use Notepad++, but am missing IntelliSense from Visual Studio.
|
I've found the latest release of NetBeans, which includes C/C++ support, to be excellent.
http://www.netbeans.org/features/cpp/index.html
|
89,588 | 89,589 |
AssignProcessToJobObject fails with "Access Denied" error when running under the debugger
|
You do AssignProcessToJobObject and it fails with "access denied" but only when you are running in the debugger. Why is this?
|
This one puzzled me for for about 30 minutes.
First off, you probably need a UAC manifest embedded in your app (as suggested here). Something like this:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<!-- Identify the application security requirements. -->
<trustInfo xmlns="urn:schemas-microsoft-com:asm.v3">
<security>
<requestedPrivileges>
<requestedExecutionLevel
level="asInvoker"
uiAccess="false"/>
</requestedPrivileges>
</security>
</trustInfo>
</assembly>
Secondly (and this is the bit I got stuck on), when you are running your app under the debugger, it creates your process in a job object. Which your child process needs to be able to breakaway from before you can assign it to your job. So (duh), you need to specify CREATE_BREAKAWAY_FROM_JOB in the flags for CreateProcess).
If you weren't running under the debugger, or your parent process were in the job, this wouldn't have happened.
|
89,767 | 90,106 |
Help on Porting a SIP library to PSP
|
I'm currently trying to port a SIP stack library (pjSIP) to the PSP Console (using the PSPSDK toolchain), but I'm having too much trouble with the makefiles (making the proper changes and solving linking issues).
Does anyone know a good text, book or something to get some insight on porting libraries?
The only documentation this project offers on porting seems too dedicated to major OS's.
|
Look at other libraries that were ported over to the PSP. Doing diffs between a linux version of a library, and a PSP version should show you.
Also, try to get to know how POSIX compatible the PSP is, that will tell you how big the job of porting the library over is.
|
90,164 | 90,994 |
Is there a way to compile C++ code to Microsoft .Net CIL (bytecode)?
|
I.e., a web browser client would be written in C++ !!!
|
There are a two choices. Managed C++ (/clr:oldSyntax, no longer maintained) or C++/CLI (definitely maintained). You'll want to use /clr:safe for in-browser software, because you wnat the browser to be able to verify it.
|
90,503 | 90,592 |
Game Development Sound Frameworks
|
I'm working with a team that's building an engine for a variety of 2D and eventually 3D mini-games. The problem we're facing is a solid, cross-platform, sound API. Obviously, DirectX is out of the question due to our needs for cross-platform capabilities. SDL is nice, and works great, but let's face it SDL_Mixer is a bit limited in what it can do. We're currently using it, but when we eventually expand to 3D, it's going to be a problem.
I've been messing with OpenAL, but most of the documentation I've found is fairly out of date, and doesn't seem to work all that great. I'm willing to learn OpenAL, and fight my way through it, but I'd like to be a bit more certain that I'm not wasting my time. Other than the DevMaster tutorials though, I haven't seen much documentation that's blown me away. If someone has some better material than I've found, that'd be awesome.
I've also seen projects such as FMOD, which seems decent despite the licensing. However, like OpenAL, they have nearly non-existant documentation. Granted, I can pour over the code to deduce my options, but it seems like a bit of a pain considering I might eventually be paying for it.
Anyways, thoughts, comments, concerns? Thanks a lot!
|
(note: I have experience with FMOD, BASS, OpenAL and DirectSound; and while I list other libraries below, I haven't used them).
BASS and FMOD are both good (and actually I liked FMOD's documentation a lot; why would you say it's "non existing"?). There are also Miles Sound System, Wwise, irrKlang and some more middleware packages.
OpenAL is supposedly cross platform, and on each platform it has it's own quirks. It's not exactly "open", either. And I'm not sure what is the future for it; it seems like it got stuck when Creative got hold of it. There's a recent effort to built the implementation from ground up, though: OpenAL Soft.
Then there are native platform APIs, like DirectSound or XAudio2 for Windows, Core Audio for OS X, ALSA for Linux, proprietary APIs for consoles etc. I think using native APIs on each platform makes a lot of sense; you just abstract it under common interface that you need, and have different implementations on each platform. Sure, it's more work than just using OpenAL, but OpenAL is not even available on some platforms, and has various quirks on other platforms that you can't even fix (because there's no source code you can fix). Licensing a commercial library like FMOD or Miles is an option in a sense that all this platform dependent work is already done for you.
We're using OpenAL at work right now, but are considering switching away from it, because it's just not going anywhere and we can't fix the quirks. So while OpenAL is easy to get started, it does not get my vote as a good option.
|
90,798 | 90,931 |
How do you place EXIF tags into a JPG, having the raw jpeg buffer in C++?
|
I am having a bit of a problem.
I get a RAW char* buffer from a camera and I need to add this tags before I can save it to disk. Writing the file to disk and reading it back again is not an option, as this will happen thousands of times.
The buffer data I receive from the camera does not contain any EXIF information, apart from the Width, Height and Pixels per Inch.
Any ideas? (C++)
|
Look at this PDF, on page 20 you have a diagram showing you were to place or modify your exif information. What is the difference with a file on disk ?
Does the JPEG buffer of your camera contain an EXIF section already ?
|
91,384 | 91,561 |
Unit testing for C++ code - Tools and methodology
|
I'm working on a large c++ system that is has been in development for a few years now. As part of an effort to improve the quality of the existing code we engaged on a large long-term refactoring project.
Do you know a good tool that can help me write unit tests in C++? Maybe something similar to Junit or Nunit?
Can anyone give some good advice on the methodology of writing unit tests for modules that were written without unit testing in mind?
|
Applying unit tests to legacy code was the very reason Working Effectively with Legacy Code was written. Michael Feathers is the author - as mentioned in other answers, he was involved in the creation of both CppUnit and CppUnitLite.
|
91,420 | 91,456 |
Export variable from C++ static library
|
I have a static library written in C++ and I have a structure describing data format, i.e.
struct Format{
long fmtId;
long dataChunkSize;
long headerSize;
Format(long, long, long);
bool operator==(Format const & other) const;
};
Some of data formats are widely used, like {fmtId=0, dataChunkSize=128, headerSize=0} and {fmtId=0, dataChunkSize=256, headerSize=0}
Some data structure classes receive format in constructor. I'd like to have some sort of shortcuts for those widely used formats, like a couple of global Format members gFmt128, gFmt256 that I can pass by reference. I instantiate them in a .cpp file like
Format gFmt128(0, 128, 0);
and in .h there is
extern Format gFmt128;
also, I declare Format const & Format::Fmt128(){return gFmt128;} and try to use it in the main module.
But if I try and do it in the main module that uses the lib, the linker complains about unresolved external gFmt128.
How can I make my library 'export' those global vars, so I can use them from other modules?
|
Don't use the static keyword on global declarations. Here is an article explain the visibility of variables with/without static. The static gives globals internal linkage, that is, only visible in the translation unit they are declared in.
|
91,511 | 91,575 |
How to wrap an existing memory buffer as a DC for GDI
|
I have a memory buffer corresponding to my screen resolution (1280x800 at 24-bits-per-pixel) that contains my screen contents at 24bpp. I want to convert this to 8-bpp (ie. Halftone color palette in Windows).
I currently do this:
1. Use CreateDIBSection to allocate a new 1280x800 24-bpp buffer and access it as a DC, as well as a plain memory buffer
2. Use memcpy to copy from my original buffer to this new buffer from step 1
3. Use BitBlt to let GDI perform the color conversion
I want to avoid the extra memcpy of step 2. To do this, I can think of two approaches:
a. Wrap my original mem buf in a DC to perform BitBlt directly from it
b. Write my own 24-bpp to 8-bpp color conversion. I can't find any info on how Windows implements this halftone color conversion. Besides even if I find out, I won't be using the accelerated features of GDI that BitBlt has access to.
So how do I do either (a) or (b)?
thanks!
|
OK, to address the two parts of the problem.
the following code shows how to get at the pixels inside of a bitmap, change them and put them back into the bitmap. You could always generate a dummy bitmap of the correct size and format, open it up, copy over your data and you then have a bitmap object with your data:
private void LockUnlockBitsExample(PaintEventArgs e)
{
// Create a new bitmap.
Bitmap bmp = new Bitmap("c:\\fakePhoto.jpg");
// Lock the bitmap's bits.
Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
System.Drawing.Imaging.BitmapData bmpData =
bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite,
bmp.PixelFormat);
// Get the address of the first line.
IntPtr ptr = bmpData.Scan0;
// Declare an array to hold the bytes of the bitmap.
int bytes = bmpData.Stride * bmp.Height;
byte[] rgbValues = new byte[bytes];
// Copy the RGB values into the array.
System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, bytes);
// Set every third value to 255. A 24bpp bitmap will look red.
for (int counter = 2; counter < rgbValues.Length; counter += 3)
rgbValues[counter] = 255;
// Copy the RGB values back to the bitmap
System.Runtime.InteropServices.Marshal.Copy(rgbValues, 0, ptr, bytes);
// Unlock the bits.
bmp.UnlockBits(bmpData);
// Draw the modified image.
e.Graphics.DrawImage(bmp, 0, 150);
}
To convert the contents to 8bpp you'll want to use the System.Drawing.Imaging.ColorMatrix class. I don't have at hand the correct matrix values for half-tone, but this example grayscales and adjustment of the values should give you an idea of the effect:
Graphics g = e.Graphics;
Bitmap bmp = new Bitmap("sample.jpg");
g.FillRectangle(Brushes.White, this.ClientRectangle);
// Create a color matrix
// The value 0.6 in row 4, column 4 specifies the alpha value
float[][] matrixItems = {
new float[] {1, 0, 0, 0, 0},
new float[] {0, 1, 0, 0, 0},
new float[] {0, 0, 1, 0, 0},
new float[] {0, 0, 0, 0.6f, 0},
new float[] {0, 0, 0, 0, 1}};
ColorMatrix colorMatrix = new ColorMatrix(matrixItems);
// Create an ImageAttributes object and set its color matrix
ImageAttributes imageAtt = new ImageAttributes();
imageAtt.SetColorMatrix(colorMatrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
// Now draw the semitransparent bitmap image.
g.DrawImage(bmp, this.ClientRectangle, 0.0f, 0.0f, bmp.Width, bmp.Height,
GraphicsUnit.Pixel, imageAtt);
imageAtt.Dispose();
I shall try and update later with the matrix values for half-tone, it's likely to be lots 0.5 or 0.333 values in there!
|
91,616 | 91,705 |
Easiest cross platform widget toolkit?
|
What is the easiest cross platform widget toolkit? I'm looking for one that minimally covers Windows, OSX, and Linux with a C or C++ interface.
|
I don't know of any I've personally used with a C API, but wxWidgets is C++. It runs on Windows, Linux, and Mac OS X. And if you're looking for easy, wxPython is a Python wrapper around wxWidgets and it is pretty easy to use.
|
91,683 | 91,872 |
How do you implement unit-testing in large scale C++ projects?
|
I believe strongly in using unit-tests as part of building large multi-platform applications. We currently are planning on having our unit-tests within a separate project. This has the benefit of keeping our code base clean. I think, however, that this would separate the test code from the implementation of the unit. What do you think of this approach and are there any tools like JUnit for c++ applications?
|
There are many Test Unit frameforks for C++.
CppUnit is certainly not the one I would choose (at least in its stable version 1.x, as it lacks many tests, and requires a lot of redundant lines of codes).
So far, my preferred framework is CxxTest, and I plan on evaluating Fructose some day.
Any way, there are a few "papers" that evaluate C++ TU frameworks :
Exploring the C++ Unit Testing Framework Jungle, By Noel Llopis
an article in Overload Journal #78
|
91,715 | 91,759 |
C++ strings without <string> and STL
|
I've not used C++ very much in the past, and have recently been doing a lot of C#, and I'm really struggling to get back into the basics of C++ again. This is particularly tricky as work mandates that none of the most handy C++ constructs can be used, so all strings must be char *'s, and there is no provision for STL lists.
What I'm currently trying to do is to create a list of strings, something which would take me no time at all using STL or in C#. Basically I want to have a function such as:
char **registeredNames = new char*[numberOfNames];
Then,
RegisterName(const * char const name, const int length)
{
//loop to see if name already registered snipped
if(notFound)
{
registeredNames[lastIndex++] = name;
}
}
or, if it was C#...
if(!registeredNames.Contains(name))
{
registeredNames.Add(name);
}
and I realize that it doesn't work. I know the const nature of the passed variables (a const pointer and a const string) makes it rather difficult, but my basic problem is that I've always avoided this situation in the past by using STL lists etc. so I've never had to work around it!
|
You'll probably need to use strcmp to see if the string is already stored:
for (int index=0; index<=lastIndex; index++)
{
if (strcmp(registeredNames[index], name) == 0)
{
return; // Already registered
}
}
Then if you really need to store a copy of the string, then you'll need to allocate a buffer and copy the characters over.
char* nameCopy = malloc(length+1);
strcpy(nameCopy, name);
registeredNames[lastIndex++] = nameCopy;
You didn't mention whether your input is NULL terminated - if not, then extra care is needed, and strcmp/strcpy won't be suitable.
|
92,039 | 92,071 |
" Attach to Process " in Visual Studio 2005
|
I installed Visual Studio 2005 ( with SP1 ) and made the default settings as what is required for C++ .
Now i open a solution and run the exe .
Under " Tools " menu item i go and Select " Attach the process " and i attach it to the exe i just ran . I put breakpoints several places in the code ( this breakpoints looks enabled ) and these are the places where the breakpoints should definitely be hit .
But for some reason , my breakpoints are not hit .
PS : All pdb's are present in correct location .
Is there any setting i am missing .
|
Perhaps it is attaching to "the wrong kind" of code.
In the "Attach to Process" dialog, there is a setting that allows you to select the kind of code you want to debug. Try clicking "Select" button next to "Attach to" text box and checking only "Managed code" the relevant code type.
http://img204.imageshack.us/img204/3017/capture5ct4.png
Most of the time, leaving "automatically determine the type of code to debug" setting on works for me. However, in some cases, the debugger is not able to understand that I want to attach to managed code (if I have launched my application from a batch file, for example) and when it does that, the above solution works for me.
|
92,396 | 92,439 |
Why can't variables be declared in a switch statement?
|
I've always wondered this - why can't you declare variables after a case label in a switch statement? In C++ you can declare variables pretty much anywhere (and declaring them close to first use is obviously a good thing) but the following still won't work:
switch (val)
{
case VAL:
// This won't work
int newVal = 42;
break;
case ANOTHER_VAL:
...
break;
}
The above gives me the following error (MSC):
initialization of 'newVal' is skipped by 'case' label
This seems to be a limitation in other languages too. Why is this such a problem?
|
Case statements are only labels. This means the compiler will interpret this as a jump directly to the label. In C++, the problem here is one of scope. Your curly brackets define the scope as everything inside the switch statement. This means that you are left with a scope where a jump will be performed further into the code skipping the initialization.
The correct way to handle this is to define a scope specific to that case statement and define your variable within it:
switch (val)
{
case VAL:
{
// This will work
int newVal = 42;
break;
}
case ANOTHER_VAL:
...
break;
}
|
92,546 | 92,641 |
Variable declarations in header files - static or not?
|
When refactoring away some #defines I came across declarations similar to the following in a C++ header file:
static const unsigned int VAL = 42;
const unsigned int ANOTHER_VAL = 37;
The question is, what difference, if any, will the static make? Note that multiple inclusion of the headers isn't possible due to the classic #ifndef HEADER #define HEADER #endif trick (if that matters).
Does the static mean only one copy of VAL is created, in case the header is included by more than one source file?
|
The static means that there will be one copy of VAL created for each source file it is included in. But it also means that multiple inclusions will not result in multiple definitions of VAL that will collide at link time. In C, without the static you would need to ensure that only one source file defined VAL while the other source files declared it extern. Usually one would do this by defining it (possibly with an initializer) in a source file and put the extern declaration in a header file.
static variables at global level are only visible in their own source file whether they got there via an include or were in the main file.
Editor's note: In C++, const objects with neither the static nor extern keywords in their declaration are implicitly static.
|
92,671 | 92,717 |
How do I reserve caret position in CEdit control?
|
I'm programming an application in MFC (don't ask) and I have a CEdit box that holds a number. When that number is edited, I would like to act on the change, and then replace the caret where it was before I acted on the change - if the user was just before the "." in "35.40", I would like it to still be placed before the dot if they change it to "345.40". I'm currently catching the CHANGE message, but that can be switched to something else (UPDATE?). How can I accomplish this?
|
Use the GetSel() function before your change to store the location of the cursor, then use SelSel() to set it back. You can use these functions to get/set the location of the caret, not just to get/set the selection the user has made.
|
92,859 | 999,810 |
What are the differences between struct and class in C++?
|
This question was already asked in the context of C#/.Net.
Now I'd like to learn the differences between a struct and a class in C++. Please discuss the technical differences as well as reasons for choosing one or the other in OO design.
I'll start with an obvious difference:
If you don't specify public: or private:, members of a struct are public by default; members of a class are private by default.
I'm sure there are other differences to be found in the obscure corners of the C++ specification.
|
You forget the tricky 2nd difference between classes and structs.
Quoth the standard (§11.2.2 in C++98 through C++11):
In absence of an access-specifier
for a base class, public is assumed
when the derived class is declared
struct and private is assumed when the class is declared class.
And just for completeness' sake, the more widely known difference between class and struct is defined in (11.2):
Member of a class defined with the
keyword class are private by
default. Members of a class defined
with the keywords struct or union
are public by default.
Additional difference: the keyword class can be used to declare template parameters, while the struct keyword cannot be so used.
|
93,039 | 93,411 |
Where are static variables stored in C and C++?
|
In what segment (.BSS, .DATA, other) of an executable file are static variables stored so that they don't have name collision?
For example:
foo.c: bar.c:
static int foo = 1; static int foo = 10;
void fooTest() { void barTest() {
static int bar = 2; static int bar = 20;
foo++; foo++;
bar++; bar++;
printf("%d,%d", foo, bar); printf("%d, %d", foo, bar);
} }
If I compile both files and link it to a main that calls fooTest() and barTest repeatedly, the printf statements increment independently. Makes sense since the foo and bar variables are local to the translation unit.
But where is the storage allocated?
To be clear, the assumption is that you have a toolchain that would output a file in ELF format. Thus, I believe that there has to be some space reserved in the executable file for those static variables.
For discussion purposes, lets assume we use the GCC toolchain.
|
Where your statics go depends on whether they are zero-initialized. zero-initialized static data goes in .BSS (Block Started by Symbol), non-zero-initialized data goes in .DATA
|
93,073 | 93,115 |
How to implement thread safe reference counting in C++
|
How do you implement an efficient and thread safe reference counting system on X86 CPUs in the C++ programming language?
I always run into the problem that the critical operations not atomic, and the available X86 Interlock operations are not sufficient for implementing the ref counting system.
The following article covers this topic, but requires special CPU instructions:
http://www.ddj.com/architect/184401888
|
Nowadays, you can use the Boost/TR1 shared_ptr<> smart pointer to keep your reference counted references.
Works great; no fuss, no muss. The shared_ptr<> class takes care of all the locking needed on the refcount.
|
93,260 | 93,291 |
A free tool to check C/C++ source code against a set of coding standards?
|
It looks quite easy to find such a tool for Java (Checkstyle, JCSC), but I can't seem to find one for C/C++. I am not looking for a lint-like static code analyzer, I only would like to check against coding standards like variable naming, capitalization, spacing, identation, bracket placement, and so on.
|
The only tool I know is Vera. Haven't used it, though, so can't comment how viable it is. Demo looks promising.
|
93,545 | 2,089,097 |
How do you detect dialup, broadband or wireless Internet connections in C++ for Windows?
|
I have an installation program (just a regular C++ MFC program, not Windows Installer based) that needs to set some registry values based on the type of Internet connection: broadband, dialup, and/or wireless. Right now this information is being determined by asking a series of yes or no questions. The problem is that the person doing the installations is not the same person that owns and uses the computer, so they're not always sure what the answers to these questions should be. Is there a way to programatically determine any of this information? The code is written in C++ (and optionally MFC) for Windows XP and up. .NET-based solutions are not an option because I don't want to have to determine if the framework is installed before our installation program can run.
To clarify, the issue is mainly that wireless and dialup connections are not "always-on", which creates a need for our product to behave a different way because our server is not always available. So a strictly speed-measuring solution wouldn't help, though there is a setting that's speed dependent so that the product doesn't try to send MB of information through a dialup connection as soon as it connects.
|
Use InternetGetConnectedState API to retrieve internet connection state.
I tested it and it works fine.
I found this document which can help:
http://www.pcausa.com/resources/InetActive.txt
|
93,569 | 93,797 |
Are POD types always aligned?
|
For example, if I declare a long variable, can I assume it will always be aligned on a "sizeof(long)" boundary? Microsoft Visual C++ online help says so, but is it standard behavior?
some more info:
a. It is possible to explicitely create a misaligned integer (*bar):
char foo[5]
int * bar = (int *)(&foo[1]);
b. Apparently, #pragma pack() only affects structures, classes, and unions.
c. MSVC documentation states that POD types are aligned to their respective sizes (but is it always or by default, and is it standard behavior, I don't know)
|
As others have mentioned, this isn't part of the standard and is left up to the compiler to implement as it sees fit for the processor in question. For example, VC could easily implement different alignment requirements for an ARM processor than it does for x86 processors.
Microsoft VC implements what is basically called natural alignment up to the size specified by the #pragma pack directive or the /Zp command line option. This means that, for example, any POD type with a size smaller or equal to 8 bytes will be aligned based on its size. Anything larger will be aligned on an 8 byte boundary.
If it is important that you control alignment for different processors and different compilers, then you can use a packing size of 1 and pad your structures.
#pragma pack(push)
#pragma pack(1)
struct Example
{
short data1; // offset 0
short padding1; // offset 2
long data2; // offset 4
};
#pragma pack(pop)
In this code, the padding1 variable exists only to make sure that data2 is naturally aligned.
Answer to a:
Yes, that can easily cause misaligned data. On an x86 processor, this doesn't really hurt much at all. On other processors, this can result in a crash or a very slow execution. For example, the Alpha processor would throw a processor exception which would be caught by the OS. The OS would then inspect the instruction and then do the work needed to handle the misaligned data. Then execution continues. The __unaligned keyword can be used in VC to mark unaligned access for non-x86 programs (i.e. for CE).
|
93,692 | 93,703 |
Which Javascript engine would you embed in your application?
|
I want to embed Javascript in a hobby game engine of mine. Now that we have the 5th generation of Javascript engines out (all blazing fast) I'm curious what engine would you choose to embed in a C++ framework (that includes actual ease of embeding it)?
Note: Just to make it clear, I'm not interested in DOM scripting or writing Javascript in a browser.
Here's a compilation of links so far and some tips from the thread
SpiderMonkey
tracemonkey (note:backwards compatible with spidermonkey):
V8
Squirrelfish
Just for the record, I love Lua and have already embedded it in game engines about 5 times at work.
However now this is a hobby project, and I think that Javascript being known by most web developers and because its ECMA, Flash and Flex developers, a game engine that uses Javascript and XML for scripting would be more user-friendly and cater to a larger user base (and one that so far has not had a chance to use their skills for games) than one with Lua (and there are plenty of those around!).
Also for the record I'll go with V8 on this one, mostly because I like it's C++ style.
|
Mozilla's SpiderMonkey is fairly easy and well-documented. It's a C API, but it's straightforward to wrap it in C++. It can be compiled to be thread-safe, which is useful for games since you'd likely want to have your main logic in one thread and user interface logic in a second thread.
Google's V8 might be a good choice, since you're using C++, but I have no experience with it yet. According to the documentation (thanks to Daniel James), V8 is not thread-safe, although this may change in the future.
There's also WebKit's SquirrelFish, but I couldn't find a standalone version of that when I was looking earlier.
|
94,227 | 94,512 |
Smart pointers: who owns the object?
|
C++ is all about memory ownership - aka ownership semantics.
It is the responsibility of the owner of a chunk of dynamically allocated memory to release that memory. So the question really becomes who owns the memory.
In C++ ownership is documented by the type a raw pointer is wrapped inside thus in a good (IMO) C++ program it is very rare (rare, not never) to see raw pointers passed around (as raw pointers have no inferred ownership thus we can not tell who owns the memory and thus without careful reading of the documentation you can't tell who is responsible for ownership).
Conversely, it is rare to see raw pointers stored in a class each raw pointer is stored within its own smart pointer wrapper. (N.B.: If you don't own an object you should not be storing it because you can not know when it will go out of scope and be destroyed.)
So the question:
What type of ownership semantic have people come across?
What standard classes are used to implement those semantics?
In what situations do you find them useful?
Lets keep 1 type of semantic ownership per answer so they can be voted up and down individually.
Summary:
Conceptually, smart pointers are simple and a naive implementation is easy. I have seen many attempted implementations, but invariably they are broken in some way that is not obvious to casual use and examples. Thus I recommend always using well tested smart pointers from a library rather than rolling your own. std::auto_ptr or one of the Boost smart pointers seem to cover all my needs.
std::auto_ptr<T>:
Single person owns the object. Transfer of ownership is allowed.
Usage: This allows you to define interfaces that show the explicit transfer of ownership.
boost::scoped_ptr<T>
Single person owns the object. Transfer of ownership is NOT allowed.
Usage: Used to show explicit ownership. Object will be destroyed by destructor or when explicitly reset.
boost::shared_ptr<T> (std::tr1::shared_ptr<T>)
Multiple ownership. This is a simple reference counted pointer. When the reference count reaches zero, the object is destroyed.
Usage: When an object can have multiple owers with a lifetime that can not be determined at compile time.
boost::weak_ptr<T>:
Used with shared_ptr<T> in situations where a cycle of pointers may happen.
Usage: Used to stop cycles from retaining objects when only the cycle is maintaining a shared refcount.
|
For me, these 3 kinds cover most of my needs:
shared_ptr - reference-counted, deallocation when the counter reaches zero
weak_ptr - same as above, but it's a 'slave' for a shared_ptr, can't deallocate
auto_ptr - when the creation and deallocation happen inside the same function, or when the object has to be considered one-owner-only ever. When you assign one pointer to another, the second 'steals' the object from the first.
I have my own implementation for these, but they are also available in Boost.
I still pass objects by reference (const whenever possible), in this case the called method must assume the object is alive only during the time of call.
There's another kind of pointer that I use that I call hub_ptr. It's when you have an object that must be accessible from objects nested in it (usually as a virtual base class). This could be solved by passing a weak_ptr to them, but it doesn't have a shared_ptr to itself. As it knows these objects wouldn't live longer than him, it passes a hub_ptr to them (it's just a template wrapper to a regular pointer).
|
94,380 | 96,724 |
Volume (Balance) Control for XP/Vista
|
Is there a method for controlling the Balance of the Wave output that will work on both XP and Vista?
|
Vista has a new api for everything related to mixers and audio, per process legacy api's should still work, but to change global volume, you would have to look at the new COM interfaces added to Vista
This should get you started
|
94,755 | 94,979 |
Best container for double-indexing
|
What is the best way (in C++) to set up a container allowing for double-indexing? Specifically, I have a list of objects, each indexed by a key (possibly multiple per key). This implies a multimap. The problem with this, however, is that it means a possibly worse-than-linear lookup to find the location of an object. I'd rather avoid duplication of data, so having each object maintain it's own coordinate and have to move itself in the map would be bad (not to mention that moving your own object may indirectly call your destructor whilst in a member function!). I would rather some container that maintains an index both by object pointer and coordinate, and that the objects themselves guarantee stable references/pointers. Then each object could store an iterator to the index (including the coordinate), sufficiently abstracted, and know where it is. Boost.MultiIndex seems like the best idea, but it's very scary and I don't wany my actual objects to need to be const.
What would you recommend?
EDIT: Boost Bimap seems nice, but does it provide stable indexing? That is, if I change the coordinate, references to other elements must remain valid. The reason I want to use pointers for indexing is because objects have otherwise no intrinsic ordering, and a pointer can remain constant while the object changes (allowing its use in a Boost MultiIndex, which, IIRC, does provide stable indexing).
|
I'm making several assumptions based on your writeup:
Keys are cheap to copy and compare
There should be only one copy of the object in the system
The same key may refer to many objects, but only one object corresponds to a given key (one-to-many)
You want to be able to efficiently look up which objects correspond to a given key, and which key corresponds to a given object
I'd suggest:
Use a linked list or some other container to maintain a global list of all objects in the system. The objects are allocated on the linked list.
Create one std::multimap<Key, Object *> that maps keys to object pointers, pointing to the single canonical location in the linked list.
Do one of:
Create one std::map<Object *, Key> that allows looking up the key attached to a particular object. Make sure your code updates this map when the key is changed. (This could also be a std::multimap if you need a many-to-many relationship.)
Add a member variable to the Object that contains the current Key (allowing O(1) lookups). Make sure your code updates this variable when the key is changed.
Since your writeup mentioned "coordinates" as the keys, you might also be interested in reading the suggestions at Fastest way to find if a 3D coordinate is already used.
|
94,794 | 95,079 |
What is the cost of a function call?
|
Compared to
Simple memory access
Disk access
Memory access on another computer(on the same network)
Disk access on another computer(on the same network)
in C++ on windows.
|
relative timings (shouldn't be off by more than a factor of 100 ;-)
memory-access in cache = 1
function call/return in cache = 2
memory-access out of cache = 10 .. 300
disk access = 1000 .. 1e8 (amortized depends upon the number of bytes transferred)
depending mostly upon seek times
the transfer itself can be pretty fast
involves at least a few thousand ops, since the user/system threshold must be crossed at least twice; an I/O request must be scheduled, the result must be written back; possibly buffers are allocated...
network calls = 1000 .. 1e9 (amortized depends upon the number of bytes transferred)
same argument as with disk i/o
the raw transfer speed can be quite high, but some process on the other computer must do the actual work
|
95,500 | 95,896 |
Can this macro be converted to a function?
|
While refactoring code and ridding myself of all those #defines that we're now taught to hate, I came across this beauty used to calculate the number of elements in a structure:
#define STRUCTSIZE(s) (sizeof(s) / sizeof(*s))
Very useful as it is but can it be converted into an inline function or template?
OK, ARRAYSIZE would be a better name but this is legacy code (no idea where it came from, it's at least 15 years old) so I pasted it 'as is'.
|
As been stated, the code actually work out the number of elements in an array, not struct. I would just write out the sizeof() division explicitly when I want it. If I were to make it a function, I would want to make it clear in its definition that it's expecting an array.
template<typename T,int SIZE>
inline size_t array_size(const T (&array)[SIZE])
{
return SIZE;
}
The above is similar to xtofl's, except it guards against passing a pointer to it (that says point to a dynamically allocated array) and getting the wrong answer by mistake.
EDIT: Simplified as per JohnMcG.
EDIT: inline.
Unfortunately, the above does not provide a compile time answer (even if the compiler does inline & optimize it to be a constant under the hood), so cannot be used as a compile time constant expression. i.e. It cannot be used as size to declare a static array. Under C++0x, this problem go away if one replaces the keyword inline by constexpr (constexpr is inline implicitly).
constexpr size_t array_size(const T (&array)[SIZE])
jwfearn's solution work for compile time, but involve having a typedef which effectively "saved" the array size in the declaration of a new name. The array size is then worked out by initialising a constant via that new name. In such case, one may as well simply save the array size into a constant from the start.
Martin York's posted solution also work under compile time, but involve using the non-standard typeof() operator. The work around to that is either wait for C++0x and use decltype (by which time one wouldn't actually need it for this problem as we'll have constexpr). Another alternative is to use Boost.Typeof, in which case we'll end up with
#include <boost/typeof/typeof.hpp>
template<typename T>
struct ArraySize
{
private: static T x;
public: enum { size = sizeof(T)/sizeof(*x)};
};
template<typename T>
struct ArraySize<T*> {};
and is used by writing
ArraySize<BOOST_TYPEOF(foo)>::size
where foo is the name of an array.
|
95,890 | 95,927 |
What is a variable's linkage and storage specifier?
|
When someone talks about a variables storage class specifier, what are they talking about?
They also often talk about variable linkage in the same context, what is that?
|
The storage class specifier controls the storage and the linkage of your variables. These are two concepts that are different.
C specifies the following specifiers for variables: auto, extern, register, static.
Storage
The storage duration determines how long your variable will live in ram.
There are three types of storage duration: static, automatic and dynamic.
static
If your variable is declared at file scope, or with an extern or static specifier, it will have static storage. The variable will exist for as long as the program is executing. No execution time is spent to create these variables.
automatic
If the variable is declared in a function, but without the extern or static specifier, it has automatic storage. The variable will exist only while you are executing the function. Once you return, the variable no longer exist. Automatic storage is typically done on the stack. It is a very fast operation to create these variables (simply increment the stack pointer by the size).
dynamic
If you use malloc (or new in C++) you are using dynamic storage. This storage will exist until you call free (or delete). This is the most expensive way to create storage, as the system must manage allocation and deallocation dynamically.
Linkage
Linkage specifies who can see and reference the variable. There are three types of linkage: internal linkage, external linkage and no linkage.
no linkage
This variable is only visible where it was declared. Typically applies to variables declared in a function.
internal linkage
This variable will be visible to all the functions within the file (called a translation unit), but other files will not know it exists.
external linkage
The variable will be visible to other translation units. These are often thought of as "global variables".
Here is a table describing the storage and linkage characteristics based on the specifiers
Storage Class Function File
Specifier Scope Scope
-----------------------------------------------------
none automatic static
no linkage external linkage
extern static static
external linkage external linkage
static static static
no linkage internal linkage
auto automatic invalid
no linkage
register automatic invalid
no linkage
|
95,956 | 96,034 |
FindNextFile fails on 64-bit Windows?
|
using C++Builder 2007, the FindFirstFile and FindNextFile functions doesn't seem to be able to find some files on 64-bit versions of Vista and XP. My test application is 32-bit.
If I use them to iterate through the folder C:\Windows\System32\Drivers they only find a handful of files although there are 185 when I issue a dir command in a command prompt. Using the same example code lists all files fine on a 32-bit version of XP.
Here is a small example program:
int main(int argc, char* argv[])
{
HANDLE hFind;
WIN32_FIND_DATA FindData;
int ErrorCode;
bool cont = true;
cout << "FindFirst/Next demo." << endl << endl;
hFind = FindFirstFile("*.*", &FindData);
if(hFind == INVALID_HANDLE_VALUE)
{
ErrorCode = GetLastError();
if (ErrorCode == ERROR_FILE_NOT_FOUND)
{
cout << "There are no files matching that path/mask\n" << endl;
}
else
{
cout << "FindFirstFile() returned error code " << ErrorCode << endl;
}
cont = false;
}
else
{
cout << FindData.cFileName << endl;
}
if (cont)
{
while (FindNextFile(hFind, &FindData))
{
cout << FindData.cFileName << endl;
}
ErrorCode = GetLastError();
if (ErrorCode == ERROR_NO_MORE_FILES)
{
cout << endl << "All files logged." << endl;
}
else
{
cout << "FindNextFile() returned error code " << ErrorCode << endl;
}
if (!FindClose(hFind))
{
ErrorCode = GetLastError();
cout << "FindClose() returned error code " << ErrorCode << endl;
}
}
return 0;
}
Running it in the C:\Windows\System32\Drivers folder on 64-bit XP returns this:
C:\WINDOWS\system32\drivers>t:\Project1.exe
FindFirst/Next demo.
.
..
AsIO.sys
ASUSHWIO.SYS
hfile.txt
raspti.zip
stcp2v30.sys
truecrypt.sys
All files logged.
A dir command on the same system returns this:
C:\WINDOWS\system32\drivers>dir/p
Volume in drive C has no label.
Volume Serial Number is E8E1-0F1E
Directory of C:\WINDOWS\system32\drivers
16-09-2008 23:12 <DIR> .
16-09-2008 23:12 <DIR> ..
17-02-2007 00:02 80.384 1394bus.sys
16-09-2008 23:12 9.453 a.txt
17-02-2007 00:02 322.560 acpi.sys
29-03-2006 14:00 18.432 acpiec.sys
24-03-2005 17:11 188.928 aec.sys
21-06-2008 15:07 291.840 afd.sys
29-03-2006 14:00 51.712 amdk8.sys
17-02-2007 00:03 111.104 arp1394.sys
08-05-2006 20:19 8.192 ASACPI.sys
29-03-2006 14:00 25.088 asyncmac.sys
17-02-2007 00:03 150.016 atapi.sys
17-02-2007 00:03 106.496 atmarpc.sys
29-03-2006 14:00 57.344 atmepvc.sys
17-02-2007 00:03 91.648 atmlane.sys
17-02-2007 00:03 569.856 atmuni.sys
24-03-2005 19:12 5.632 audstub.sys
29-03-2006 14:00 6.144 beep.sys
Press any key to continue . . .
etc.
I'm puzzled. What is the reason for this?
Brian
|
Is there redirection going on? See the remarks on Wow64DisableWow64FsRedirection http://msdn.microsoft.com/en-gb/library/aa365743.aspx
|
96,196 | 96,268 |
When are C++ macros beneficial?
|
The C preprocessor is justifiably feared and shunned by the C++ community. In-lined functions, consts and templates are usually a safer and superior alternative to a #define.
The following macro:
#define SUCCEEDED(hr) ((HRESULT)(hr) >= 0)
is in no way superior to the type safe:
inline bool succeeded(int hr) { return hr >= 0; }
But macros do have their place, please list the uses you find for macros that you can't do without the preprocessor.
Please put each use-cases in a seperate answer so it can be voted up and if you know of how to achieve one of the answers without the preprosessor point out how in that answer's comments.
|
As wrappers for debug functions, to automatically pass things like __FILE__, __LINE__, etc:
#ifdef ( DEBUG )
#define M_DebugLog( msg ) std::cout << __FILE__ << ":" << __LINE__ << ": " << msg
#else
#define M_DebugLog( msg )
#endif
Since C++20 the magic type std::source_location can however be used instead of __LINE__ and __FILE__ to implement an analogue as a normal function (template).
|
96,233 | 96,263 |
Why would I use 2's complement to compare two doubles instead of comparing their differences against an epsilon value?
|
Referenced here and here...Why would I use two's complement over an epsilon method? It seems like the epsilon method would be good enough for most cases.
Update: I'm purely looking for a theoretical reason why you'd use one over the other. I've always used the epsilon method.
Has anyone used the 2's complement comparison successfully? Why? Why Not?
|
the second link you reference mentions an article that has quite a long description of the issue:
http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm
but unless you are tweaking performance I would stick with epsilon so people can debug your code
|
96,414 | 101,720 |
C++: Step 1: ExtractIconEx. Step 2: ??? Step 3: SetMenuItemBitmaps
|
I'm experimenting with adding icons to a shell extension. I have this code (sanitized for easy reading), which works:
InsertMenu(hmenu, index, MF_POPUP|MF_BYPOSITION, (UINT)hParentMenu, namestring);
The next step is this code:
HICON hIconLarge, hIconSmall;
ICONINFO oIconInfo;
ExtractIconEx("c:\\progra~1\\winzip\\winzip32.exe", 0, &hIconLarge, &hIconSmall, 1);
GetIconInfo(hIconSmall, &oIconInfo);
//???????
SetMenuItemBitmaps(hParentMenu, indexMenu-1, MF_BITMAP | MF_BYPOSITION, hbmp, hbmp);
What do I put in to replace the ?'s. Attempts to Google this knowledge have found many tips that I failed to get working. Any advice on getting this to work, especially on older machines (e.g. no .net framework, no vista) is appreciated.
|
This works, though the back color is black instead of transparent.
GetIconInfo(hIconSmall, &oIconInfo);
SetMenuItemBitmaps(hmenu, uMenuIndex+i+popUpMenuCount-1, MF_BITMAP | MF_BYPOSITION, oIconInfo.hbmColor, oIconInfo.hbmColor);
|
96,500 | 96,530 |
Is there anything wrong with returning default constructed values?
|
Suppose I have the following code:
class some_class{};
some_class some_function()
{
return some_class();
}
This seems to work pretty well and saves me the trouble of having to declare a variable just to make a return value. But I don't think I've ever seen this in any kind of tutorial or reference. Is this a compiler-specific thing (visual C++)? Or is this doing something wrong?
|
No this is perfectly valid. This will also be more efficient as the compiler is actually able to optimise away the temporary.
|
96,579 | 97,536 |
STL vectors with uninitialized storage?
|
I'm writing an inner loop that needs to place structs in contiguous storage. I don't know how many of these structs there will be ahead of time. My problem is that STL's vector initializes its values to 0, so no matter what I do, I incur the cost of the initialization plus the cost of setting the struct's members to their values.
Is there any way to prevent the initialization, or is there an STL-like container out there with resizeable contiguous storage and uninitialized elements?
(I'm certain that this part of the code needs to be optimized, and I'm certain that the initialization is a significant cost.)
Also, see my comments below for a clarification about when the initialization occurs.
SOME CODE:
void GetsCalledALot(int* data1, int* data2, int count) {
int mvSize = memberVector.size()
memberVector.resize(mvSize + count); // causes 0-initialization
for (int i = 0; i < count; ++i) {
memberVector[mvSize + i].d1 = data1[i];
memberVector[mvSize + i].d2 = data2[i];
}
}
|
std::vector must initialize the values in the array somehow, which means some constructor (or copy-constructor) must be called. The behavior of vector (or any container class) is undefined if you were to access the uninitialized section of the array as if it were initialized.
The best way is to use reserve() and push_back(), so that the copy-constructor is used, avoiding default-construction.
Using your example code:
struct YourData {
int d1;
int d2;
YourData(int v1, int v2) : d1(v1), d2(v2) {}
};
std::vector<YourData> memberVector;
void GetsCalledALot(int* data1, int* data2, int count) {
int mvSize = memberVector.size();
// Does not initialize the extra elements
memberVector.reserve(mvSize + count);
// Note: consider using std::generate_n or std::copy instead of this loop.
for (int i = 0; i < count; ++i) {
// Copy construct using a temporary.
memberVector.push_back(YourData(data1[i], data2[i]));
}
}
The only problem with calling reserve() (or resize()) like this is that you may end up invoking the copy-constructor more often than you need to. If you can make a good prediction as to the final size of the array, it's better to reserve() the space once at the beginning. If you don't know the final size though, at least the number of copies will be minimal on average.
In the current version of C++, the inner loop is a bit inefficient as a temporary value is constructed on the stack, copy-constructed to the vectors memory, and finally the temporary is destroyed. However the next version of C++ has a feature called R-Value references (T&&) which will help.
The interface supplied by std::vector does not allow for another option, which is to use some factory-like class to construct values other than the default. Here is a rough example of what this pattern would look like implemented in C++:
template <typename T>
class my_vector_replacement {
// ...
template <typename F>
my_vector::push_back_using_factory(F factory) {
// ... check size of array, and resize if needed.
// Copy construct using placement new,
new(arrayData+end) T(factory())
end += sizeof(T);
}
char* arrayData;
size_t end; // Of initialized data in arrayData
};
// One of many possible implementations
struct MyFactory {
MyFactory(int* p1, int* p2) : d1(p1), d2(p2) {}
YourData operator()() const {
return YourData(*d1,*d2);
}
int* d1;
int* d2;
};
void GetsCalledALot(int* data1, int* data2, int count) {
// ... Still will need the same call to a reserve() type function.
// Note: consider using std::generate_n or std::copy instead of this loop.
for (int i = 0; i < count; ++i) {
// Copy construct using a factory
memberVector.push_back_using_factory(MyFactory(data1+i, data2+i));
}
}
Doing this does mean you have to create your own vector class. In this case it also complicates what should have been a simple example. But there may be times where using a factory function like this is better, for instance if the insert is conditional on some other value, and you would have to otherwise unconditionally construct some expensive temporary even if it wasn't actually needed.
|
97,050 | 101,980 |
std::map insert or std::map find?
|
Assuming a map where you want to preserve existing entries. 20% of the time, the entry you are inserting is new data. Is there an advantage to doing std::map::find then std::map::insert using that returned iterator? Or is it quicker to attempt the insert and then act based on whether or not the iterator indicates the record was or was not inserted?
|
The answer is you do neither. Instead you want to do something suggested by Item 24 of Effective STL by Scott Meyers:
typedef map<int, int> MapType; // Your map type may vary, just change the typedef
MapType mymap;
// Add elements to map here
int k = 4; // assume we're searching for keys equal to 4
int v = 0; // assume we want the value 0 associated with the key of 4
MapType::iterator lb = mymap.lower_bound(k);
if(lb != mymap.end() && !(mymap.key_comp()(k, lb->first)))
{
// key already exists
// update lb->second if you care to
}
else
{
// the key does not exist in the map
// add it to the map
mymap.insert(lb, MapType::value_type(k, v)); // Use lb as a hint to insert,
// so it can avoid another lookup
}
|
97,081 | 97,229 |
"get() const" vs. "getAsConst() const"
|
Someone told me about a C++ style difference in their team. I have my own viewpoint on the subject, but I would be interested by pros and cons coming from everyone.
So, in case you have a class property you want to expose via two getters, one read/write, and the other, readonly (i.e. there is no set method). There are at least two ways of doing it:
class T ;
class MethodA
{
public :
const T & get() const ;
T & get() ;
// etc.
} ;
class MethodB
{
public :
const T & getAsConst() const ;
T & get() ;
// etc.
} ;
What would be the pros and the cons of each method?
I am interested more by C++ technical/semantic reasons, but style reasons are welcome, too.
Note that MethodB has one major technical drawback (hint: in generic code).
|
Well, for one thing, getAsConst must be called when the 'this' pointer is const -- not when you want to receive a const object. So, alongside any other issues, it's subtly misnamed. (You can still call it when 'this' is non-const, but that's neither here nor there.)
Ignoring that, getAsConst earns you nothing, and puts an undue burden on the developer using the interface. Instead of just calling "get" and knowing he's getting what he needs, now he has to ascertain whether or not he's currently using a const variable, and if the new object he's grabbing needs to be const. And later, if both objects become non-const due to some refactoring, he's got to switch out his call.
|
97,338 | 99,282 |
GCC dependency generation for a different output directory
|
I'm using GCC to generate a dependency file, but my build rules put the output into a subdirectory. Is there a way to tell GCC to put my subdirectory prefix in the dependency file it generates for me?
gcc $(INCLUDES) -E -MM $(CFLAGS) $(SRC) >>$(DEP)
|
The answer is in the GCC manual: use the -MT flag.
-MT target
Change the target of the rule emitted by dependency generation. By default CPP takes the name of the main input file, deletes any directory components and any file suffix such as .c, and appends the platform's usual object suffix. The result is the target.
An -MT option will set the target to be exactly the string you specify. If you want multiple targets, you can specify them as a single argument to -MT, or use multiple -MT options.
For example, -MT '$(objpfx)foo.o' might give
$(objpfx)foo.o: foo.c
|
97,987 | 98,024 |
Advantage of switch over if-else statement
|
What's the best practice for using a switch statement vs using an if statement for 30 unsigned enumerations where about 10 have an expected action (that presently is the same action). Performance and space need to be considered but are not critical. I've abstracted the snippet so don't hate me for the naming conventions.
switch statement:
// numError is an error enumeration type, with 0 being the non-error case
// fire_special_event() is a stub method for the shared processing
switch (numError)
{
case ERROR_01 : // intentional fall-through
case ERROR_07 : // intentional fall-through
case ERROR_0A : // intentional fall-through
case ERROR_10 : // intentional fall-through
case ERROR_15 : // intentional fall-through
case ERROR_16 : // intentional fall-through
case ERROR_20 :
{
fire_special_event();
}
break;
default:
{
// error codes that require no additional action
}
break;
}
if statement:
if ((ERROR_01 == numError) ||
(ERROR_07 == numError) ||
(ERROR_0A == numError) ||
(ERROR_10 == numError) ||
(ERROR_15 == numError) ||
(ERROR_16 == numError) ||
(ERROR_20 == numError))
{
fire_special_event();
}
|
Use switch.
In the worst case the compiler will generate the same code as a if-else chain, so you don't lose anything. If in doubt put the most common cases first into the switch statement.
In the best case the optimizer may find a better way to generate the code. Common things a compiler does is to build a binary decision tree (saves compares and jumps in the average case) or simply build a jump-table (works without compares at all).
|
98,242 | 98,256 |
Post increment operator behavior
|
Possible Duplicate:
Pre & post increment operator behavior in C, C++, Java, & C#
Here is a test case:
void foo(int i, int j)
{
printf("%d %d", i, j);
}
...
test = 0;
foo(test++, test);
I would expect to get a "0 1" output, but I get "0 0"
What gives??
|
This is an example of unspecified behavior. The standard does not say what order arguments should be evaluated in. This is a compiler implementation decision. The compiler is free to evaluate the arguments to the function in any order.
In this case, it looks like actually processes the arguments right to left instead of the expected left to right.
In general, doing side-effects in arguments is bad programming practice.
Instead of foo(test++, test); you should write foo(test, test+1); test++;
It would be semantically equivalent to what you are trying to accomplish.
Edit:
As Anthony correctly points out, it is undefined to both read and modify a single variable without an intervening sequence point. So in this case, the behavior is indeed undefined. So the compiler is free to generate whatever code it wants.
|
98,586 | 98,977 |
Where can I find the world's fastest atof implementation?
|
I'm looking for an extremely fast atof() implementation on IA32 optimized for US-en locale, ASCII, and non-scientific notation. The windows multithreaded CRT falls down miserably here as it checks for locale changes on every call to isdigit(). Our current best is derived from the best of perl + tcl's atof implementation, and outperforms msvcrt.dll's atof by an order of magnitude. I want to do better, but am out of ideas. The BCD related x86 instructions seemed promising, but I couldn't get it to outperform the perl/tcl C code. Can any SO'ers dig up a link to the best out there? Non x86 assembly based solutions are also welcome.
Clarifications based upon initial answers:
Inaccuracies of ~2 ulp are fine for this application.
The numbers to be converted will arrive in ascii messages over the network in small batches and our application needs to convert them in the lowest latency possible.
|
What is your accuracy requirement? If you truly need it "correct" (always gets the nearest floating-point value to the decimal specified), it will probably be hard to beat the standard library versions (other than removing locale support, which you've already done), since this requires doing arbitrary precision arithmetic. If you're willing to tolerate an ulp or two of error (and more than that for subnormals), the sort of approach proposed by cruzer's can work and may be faster, but it definitely will not produce <0.5ulp output. You will do better accuracy-wise to compute the integer and fractional parts separately, and compute the fraction at the end (e.g. for 12345.6789, compute it as 12345 + 6789 / 10000.0, rather than 6*.1 + 7*.01 + 8*.001 + 9*0.0001) since 0.1 is an irrational binary fraction and error will accumulate rapidly as you compute 0.1^n. This also lets you do most of the math with integers instead of floats.
The BCD instructions haven't been implemented in hardware since (IIRC) the 286, and are simply microcoded nowadays. They are unlikely to be particularly high-performance.
|
98,705 | 100,593 |
What are the semantics of a const member function?
|
I understand that the function is not allowed to change the state of the object, but I thought I read somewhere that the compiler was allowed to assume that if the function was called with the same arguments, it would return the same value and thus could reuse a cached value if it was available. e.g.
class object
{
int get_value(int n) const
{
...
}
...
object x;
int a = x.get_value(1);
...
int b = x.get_value(1);
then the compiler could optimize the second call away and either use the value in a register or simply do b = a;
Is this true?
|
const is about program semantics and not about implementation details. You should mark a member function const when it does not change the visible state of the object, and should be callable on an object that is itself const. Within a const member function on a class X, the type of this is X const *: pointer to constant X object. Thus all member variables are effectively const within that member function (except mutable ones). If you have a const object, you can only call const member functions on it.
You can use mutable to indicate that a member variable may change even within a const member function. This is typically used to identify variables used for caching results, or for variables that don't affect the actual observable state such as mutexes (you still need to lock the mutex in the const member functions) or use counters.
class X
{
int data;
mutable boost::mutex m;
public:
void set_data(int i)
{
boost::lock_guard<boost::mutex> lk(m);
data=i;
}
int get_data() const // we want to be able to get the data on a const object
{
boost::lock_guard<boost::mutex> lk(m); // this requires m to be non-const
return data;
}
};
If you hold the data by pointer rather than directly (including smart pointers such as std::auto_ptr or boost::shared_ptr) then the pointer becomes const in a const member function, but not the pointed-to data, so you can modify the pointed-to data.
As for caching: in general the compiler cannot do this because the state might change between calls (especially in my multi-threaded example with the mutex). However, if the definition is inline then the compiler can pull the code into the calling function and optimize what it can see there. This might result in the function effectively only being called once.
The next version of the C++ Standard (C++0x) will have a new keyword constexpr. Functions tagged constexpr return a constant value, so the results can be cached. There are limits on what you can do in such a function (in order that the compiler can verify this fact).
|
99,474 | 99,503 |
how to handle code that is deemed dangerous to change, but stable?
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What is the best way to handle a big team that has access to a stable but no so pretty code, that is easy to introduce bugs into?
I'm looking for something along the lines of SVN locking the file(s).
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Write unit tests if you don't have them already. Then start refactoring, and keep doing regression tests upon every commit.
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