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54,047 | 54,056 |
Regex's For Developers
|
I've been trying to figure out a regex to allow me to search for a particular string while automatically skipping comments. Anyone have an RE like this or know of one? It doesn't even need to be sophisticated enough to skip #if 0 blocks; I just want it to skip over // and /* blocks. The converse, that is only search inside comment blocks, would be very useful too.
Environment: VS 2003
|
This is a harder problem than it might at first appear, since you need to consider comment tokens inside strings, comment tokens that are themselves commented out etc.
I wrote a string and comment parser for C#, let me see if I can dig out something that will help... I'll update if I find anything.
EDIT:
... ok, so I found my old 'codemasker' project. Turns out that I did this in stages, not with a single regex. Basically I inch through a source file looking for start tokens, when I find one I then look for an end-token and mask everything in between. This takes into account the context of the start token... if you find a token for "string start" then you can safely ignore comment tokens until you find the end of the string, and vice versa. Once the code is masked (I used guids as masks, and a hashtable to keep track) then you can safely do your search and replace, then finally restore the masked code.
Hope that helps.
|
54,142 | 54,146 |
How does the Comma Operator work
|
How does the comma operator work in C++?
For instance, if I do:
a = b, c;
Does a end up equaling b or c?
(Yes, I know this is easy to test - just documenting on here for someone to find the answer quickly.)
Update: This question has exposed a nuance when using the comma operator. Just to document this:
a = b, c; // a is set to the value of b!
a = (b, c); // a is set to the value of c!
This question was actually inspired by a typo in code. What was intended to be
a = b;
c = d;
Turned into
a = b, // <- Note comma typo!
c = d;
|
It would be equal to b.
The comma operator has a lower precedence than assignment.
|
54,188 | 54,444 |
Are C++ Reads and Writes of an int Atomic?
|
I have two threads, one updating an int and one reading it. This is a statistic value where the order of the reads and writes is irrelevant.
My question is, do I need to synchronize access to this multi-byte value anyway? Or, put another way, can part of the write be complete and get interrupted, and then the read happen.
For example, think of a value = 0x0000FFFF that gets incremented value of 0x00010000.
Is there a time where the value looks like 0x0001FFFF that I should be worried about? Certainly the larger the type, the more possible something like this to happen.
I've always synchronized these types of accesses, but was curious what the community thinks.
|
At first one might think that reads and writes of the native machine size are atomic but there are a number of issues to deal with including cache coherency between processors/cores. Use atomic operations like Interlocked* on Windows and the equivalent on Linux. C++0x will have an "atomic" template to wrap these in a nice and cross-platform interface. For now if you are using a platform abstraction layer it may provide these functions. ACE does, see the class template ACE_Atomic_Op.
|
54,585 | 54,596 |
When should you use a class vs a struct in C++?
|
In what scenarios is it better to use a struct vs a class in C++?
|
The differences between a class and a struct in C++ are:
struct members and base classes/structs are public by default.
class members and base classes/structs are private by default.
Both classes and structs can have a mixture of public, protected and private members, can use inheritance, and can have member functions.
I would recommend you:
use struct for plain-old-data structures without any class-like features;
use class when you make use of features such as private or protected members, non-default constructors and operators, etc.
|
54,674 | 54,742 |
Any good building tools for a C++ project, which can replace make?
|
i'm wondering if there is any nice and neat tool to replace the GNU Autotools or Make to build a very large C++ project, which are such a complicated thing to use.
It is simple to generate all the files that de Autotools require if the project is small, but if the source code is divided in many directories, with multiple third party libraries and many dependencies, you fall into the "Autotools Hell"..
thanks for any recommendations
|
The Google V8 JavaScript Engine is written in C++ and uses SCons, so I guess that's one vote for it.
|
55,093 | 55,149 |
How to deal with arrays (declared on the stack) in C++?
|
I have a class to parse a matrix that keeps the result in an array member:
class Parser
{
...
double matrix_[4][4];
};
The user of this class needs to call an API function (as in, a function I have no control over, so I can't just change its interface to make things work more easily) that looks like this:
void api_func(const double matrix[4][4]);
The only way I have come up with for the caller to pass the array result to the function is by making the member public:
void myfunc()
{
Parser parser;
...
api_func(parser.matrix_);
}
Is this the only way to do things? I'm astounded by how inflexible multidimensional arrays declared like this are. I thought matrix_ would essentially be the same as a double** and I could cast (safely) between the two. As it turns out, I can't even find an unsafe way to cast between the things. Say I add an accessor to the Parser class:
void* Parser::getMatrix()
{
return (void*)matrix_;
}
This will compile, but I can't use it, because there doesn't seem to be a way to cast back to the weirdo array type:
// A smorgasbord of syntax errors...
api_func((double[][])parser.getMatrix());
api_func((double[4][4])parser.getMatrix());
api_func((double**)parser.getMatrix()); // cast works but it's to the wrong type
The error is:
error C2440: 'type cast' : cannot convert from 'void *' to 'const double [4][4]'
...with an intriguing addendum:
There are no conversions to array types, although there are conversions to references or pointers to arrays
I can't determine how to cast to a reference or pointer to array either, albeit that it probably won't help me here.
To be sure, at this point the matter is purely academic, as the void* casts are hardly cleaner than a single class member left public!
|
Here's a nice, clean way:
class Parser
{
public:
typedef double matrix[4][4];
// ...
const matrix& getMatrix() const
{
return matrix_;
}
// ...
private:
matrix matrix_;
};
Now you're working with a descriptive type name rather than an array, but since it's a typedef the compiler will still allow passing it to the unchangeable API function that takes the base type.
|
55,440 | 55,446 |
Checking Inheritance with templates in C++
|
I've a class which is a wrapper class(serves as a common interface) around another class implementing the functionality required. So my code looks like this.
template<typename ImplemenationClass> class WrapperClass {
// the code goes here
}
Now, how do I make sure that ImplementationClass can be derived from a set of classes only, similar to java's generics
<? extends BaseClass>
syntax?
|
It's verbose, but you can do it like this:
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_base_of.hpp>
struct base {};
template <typename ImplementationClass, class Enable = void>
class WrapperClass;
template <typename ImplementationClass>
class WrapperClass<ImplementationClass,
typename boost::enable_if<
boost::is_base_of<base,ImplementationClass> >::type>
{};
struct derived : base {};
struct not_derived {};
int main() {
WrapperClass<derived> x;
// Compile error here:
WrapperClass<not_derived> y;
}
This requires a compiler with good support for the standard (most recent compilers should be fine but old versions of Visual C++ won't be). For more information, see the Boost.Enable_If documentation.
As Ferruccio said, a simpler but less powerful implementation:
#include <boost/static_assert.hpp>
#include <boost/type_traits/is_base_of.hpp>
struct base {};
template <typename ImplementationClass>
class WrapperClass
{
BOOST_STATIC_ASSERT((
boost::is_base_of<base, ImplementationClass>::value));
};
|
55,451 | 55,477 |
Which C# project type would you use to redevelop a MFC C++ activex control?
|
Looking at the C# project templates in VS2008 and the offerings are WPF User Control Library, WPF Custom Control Library and Windows Forms Control Library. Which of these would you use if you wanted to move a legacy active control written in c++ into the world of C# and .NET?
|
It sounds like you are trying to do several different things all at once:
Migrate your code to building in a newer version of visual studio.
Migrate your use of technology to a newer technology (ActiveX to .net)
Migrate your language (c++ to c#).
If you have a small codebase you are probably as well to start from scratch and port functionality into the new codebase as required.
For a larger codebase you need to realize that this is an expensive task both in effort and defect rate.
An order might be:
Import your code into the newer version of visual studio. Get it compiling. Review the project settings for each project.
Refactor your code to isolate the mfc and activex code as much as possible. Follow good refactoring practices especially if don't have many unit tests before you start.
Consider replacing your ActiveX layer with .net.
Consider which GUI toolkit is best for replacing MFC.
Language - consider moving first to managed c++.
Consider moving from managed c++ to c#.
Most importantly be able to justify doing all of the above!
|
55,510 | 55,548 |
When do function-level static variables get allocated/initialized?
|
I'm quite confident that globally declared variables get allocated (and initialized, if applicable) at program start time.
int globalgarbage;
unsigned int anumber = 42;
But what about static ones defined within a function?
void doSomething()
{
static bool globalish = true;
// ...
}
When is the space for globalish allocated? I'm guessing when the program starts. But does it get initialized then too? Or is it initialized when doSomething() is first called?
|
I was curious about this so I wrote the following test program and compiled it with g++ version 4.1.2.
include <iostream>
#include <string>
using namespace std;
class test
{
public:
test(const char *name)
: _name(name)
{
cout << _name << " created" << endl;
}
~test()
{
cout << _name << " destroyed" << endl;
}
string _name;
};
test t("global variable");
void f()
{
static test t("static variable");
test t2("Local variable");
cout << "Function executed" << endl;
}
int main()
{
test t("local to main");
cout << "Program start" << endl;
f();
cout << "Program end" << endl;
return 0;
}
The results were not what I expected. The constructor for the static object was not called until the first time the function was called. Here is the output:
global variable created
local to main created
Program start
static variable created
Local variable created
Function executed
Local variable destroyed
Program end
local to main destroyed
static variable destroyed
global variable destroyed
|
55,532 | 55,660 |
Casting between multi- and single-dimentional arrays
|
This came up from this answer to a previous question of mine.
Is it guaranteed for the compiler to treat array[4][4] the same as array[16]?
For instance, would either of the below calls to api_func() be safe?
void api_func(const double matrix[4][4]);
// ...
{
typedef double Matrix[4][4];
double* array1 = new double[16];
double array2[16];
// ...
api_func(reinterpret_cast<Matrix&>(array1));
api_func(reinterpret_cast<Matrix&>(array2));
}
|
From the C++ standard, referring to the sizeof operator:
When applied to an array, the result is the total number of bytes in the array. This implies that the size of an array of n elements is n times the size of an element.
From this, I'd say that double[4][4] and double[16] would have to have the same underlying representation.
I.e., given
sizeof(double[4]) = 4*sizeof(double)
and
sizeof(double[4][4]) = 4*sizeof(double[4])
then we have
sizeof(double[4][4]) = 4*4*sizeof(double) = 16*sizeof(double) = sizeof(double[16])
I think a standards-compliant compiler would have to implement these the same, and I think that this isn't something that a compiler would accidentally break. The standard way of implementing multi-dimensional arrays works as expected. Breaking the standard would require extra work, for likely no benefit.
The C++ standard also states that an array consists of contiguously-allocated elements, which eliminates the possibility of doing anything strange using pointers and padding.
|
55,641 | 55,650 |
Unicode Processing in C++
|
What is the best practice of Unicode processing in C++?
|
Use ICU for dealing with your data (or a similar library)
In your own data store, make sure everything is stored in the same encoding
Make sure you are always using your unicode library for mundane tasks like string length, capitalization status, etc. Never use standard library builtins like is_alpha unless that is the definition you want.
I can't say it enough: never iterate over the indices of a string if you care about correctness, always use your unicode library for this.
|
55,753 | 55,885 |
Creating Custom Performance Counters in Visual C++
|
Does anybody know of a method for creating custom Performance Counters using ordinary unmanaged Visual C++?
I know that it can be done easily using managed C++, but I need to do it using an unmanaged Windows service.
I also know that you can retrieve performance counter data, but I need to create some custom counters and increment them during the applications runtime.
|
See here:
http://msdn.microsoft.com/en-us/library/aa371925.aspx
It is not really hard, but a bit tedious as the API involves extensive usage of self-referential, variable-length structures and has to employ some IPC mechanism to obtain the data from the monitored process.
|
55,859 | 55,863 |
How can I catch all types of exceptions in one catch block?
|
In C++, I'm trying to catch all types of exceptions in one catch (like catch(Exception) in C#). How is it done? And what's more, how can one catch divide-by-zero exceptions?
|
catch (...)
{
// Handle exceptions not covered.
}
Important considerations:
A better approach is to catch specific types of exception that you can actually recover from as opposed to all possible exceptions.
catch(...) will also catch certain serious system level exceptions (varies depending on compiler) that you are not going to be able to recover reliably from. Catching them in this way and then swallowing them and continuing could cause further serious problems in your program.
Depending on your context it can be acceptable to use catch(...), providing the exception is re-thrown. In this case, you log all useful local state information and then re-throw the exception to allow it to propagate up. However you should read up on the RAII pattern if you choose this route.
|
56,046 | 56,080 |
Stop system entering 'standby'
|
How can i stop the host machine entering standby mode while my application is running?
Is there any win32 api call to do this?
|
There are two APIs, depending on what version of Windows.
XP,2000, 2003:
http://msdn.microsoft.com/en-us/library/aa373247(VS.85).aspx
Respond to PBT_APMQUERYSUSPEND.
Vista, 2008:
http://msdn.microsoft.com/en-us/library/aa373208(VS.85).aspx
There could be many valid reasons to prevent the computer from going to sleep. For example, watching a video, playing music, compiling a long running build, downloading large files, etc.
|
56,091 | 56,111 |
Pointers to C++ class methods
|
Whilst refactoring some legacy C++ code I found that I could potentially remove some code duplication by somehow defining a variable that could point to any class method that shared the same signature. After a little digging, I found that I could do something like the following:
class MyClass
{
protected:
bool CaseMethod1( int abc, const std::string& str )
{
cout << "case 1:" << str;
return true;
}
bool CaseMethod2( int abc, const std::string& str )
{
cout << "case 2:" << str;
return true;
}
bool CaseMethod3( int abc, const std::string& str )
{
cout << "case 3:" << str;
return true;
}
public:
bool TestSwitch( int num )
{
bool ( MyClass::*CaseMethod )( int, const std::string& );
switch ( num )
{
case 1: CaseMethod = &MyClass::CaseMethod1;
break;
case 2: CaseMethod = &MyClass::CaseMethod2;
break;
case 3: CaseMethod = &MyClass::CaseMethod3;
break;
}
...
bool res = CaseMethod( 999, "hello world" );
...
reurn res;
}
};
My question is - is this the correct way to go about this? Should I consider anything that Boost has to offer?
Edit...
Ok, my mistake - I should be calling the method like so:
bool res = ( (*this).*CaseMethod )( 999, "Hello World" );
|
What you have there is a pointer-to-member-function. It will solve your problem. I am surprised that your "TestSwitch" function compiles, as the calling syntax is slightly different to what you might expect. It should be:
bool res = (this->*CaseMethod)( 999, "hello world" );
However, you might find a combination of boost::function and boost::bind makes things a little easier, as you can avoid the bizarre calling syntax.
boost::function<bool(int,std::string)> f=
boost::bind(&MyClass::CaseMethod1,this,_1,_2);
Of course, this will bind it to the current this pointer: you can make the this pointer of the member function an explicit third parameter if you like:
boost::function<bool(MyClass*,int,std::string)> f=
boost::bind(&MyClass::CaseMethod1,_1,_2,_3);
Another alternative might be to use virtual functions and derived classes, but that might require major changes to your code.
|
56,145 | 87,399 |
MFC IE embedded web browser wackiness
|
I have this modeless MFC dialog which embeds an Internet Explorer web browser control.
The control is derived straight from CWnd with ActiveX wrappers generated by Visual Studio, and I map it to the CDialog using only a DDX_Control(pDX, IDC_EXPLORER, m_explorer);.
I have 2 problems.
Problem #1:
Being modeless, I start and stop the dialog at my own pleasure using new/Create(), then DestroyWindow()/delete(in PostNcDestroy).
Trouble begins when the IE control starts loading a Flash video (regular YouTube stuff): when one closes, thus destroying the dialog, the video still loads! Right until fully cached. The Flash ActiveX thread still lingers and continues to run even when the parent dialog has passed PostNcDestroy and all memory was freed.
What to do? How do you trully 'kill' that child web control and all its threads?
Problem #2:
The web browser control covers the whole area of the dialog. I cannot intercept any OnMouseMove() - in the parent dialog or in the web browser mapping class! What gives?
Thanks!
"Cleanup"
"delete this" in PostNcDestroy() - and calling the base func of course. Should it be more? What? Shouldn't the dialog gracefully take care of its children?
I tried to explicitly call DestroyWindow on the web control, or send/post him messages like WM_DESTROY, WM_CLOSE, even WM_QUIT - but nothing - same deal.
Problem #2:
No, like indented, the control takes all space and it's on top so I guess any mouse action doesn't get transmitted 'bellow' :)? But then why doesn't his own OnMouseMove get called? Because it goes straight from CWnd? I'm lost...
|
problem 1) try myBrowser.navigate("about:blank") before destroying the window.
|
56,340 | 154,326 |
Can I set a data breakpoint in runtime in System C (or in Plain Vanilla C++)?
|
I have a class in system-C with some data members as such:
long double x[8];
I'm initializing it in the construction like this:
for (i = 0; i < 8; ++i) {
x[i] = 0;
}
But the first time I use it in my code I have garbage there.
Because of the way the system is built I can't connect a debugger easily. Are there any methods to set a data breakpoint in the code so that it tells me where in the code the variables were actually changed, but without hooking up a debugger?
Edit:
@Prakash:
Actually, this is a typo in the question, but not in my code... Thanks!
|
You could try starting a second thread which spins, looking for changes in the variable:
#include <pthread.h>
void *ThreadProc(void *arg)
{
volatile long double *x = (volatile long double *)arg;
while(1)
{
for(int i = 0; i < 8; i++)
{
if(x[i] != 0)
{
__asm__ __volatile__ ("int 3"); // breakpoint (x86)
}
}
return 0; // Never reached, but placate the compiler
}
...
pthread_t threadID;
pthread_create(&threadID, NULL, ThreadProc, &x[0]);
This will raise a SIGTRAP signal to your application whenever any of the x values is not zero.
|
56,347 | 56,370 |
Iterators in C++ (stl) vs Java, is there a conceptual difference?
|
I'm returning to c++ after being away for a bit and trying to dust off the old melon.
In Java Iterator is an interface to a container having methods: hasNext(), next() and remove(). The presence of hasNext() means it has the concept of a limit for the container being traversed.
//with an Iterator
Iterator<String> iter = trees.iterator();
while (iter.hasNext())
{
System.out.println(iter.next());
}
In the C++ standard template library, iterators seem to represent a datatype or class the supports the operator++ and operator== but has no concept of a limit built in so comparison is required before advancing to the next item. The limit has to checked by the user comparing two iterators in the normal case the second iterator is the container end.
vector<int> vec;
vector<int>::iterator iter;
// Add some elements to vector
v.push_back(1);
v.push_back(4);
v.push_back(8);
for (iter= v.begin(); iter != v.end(); iter++)
{
cout << *i << " "; //Should output 1 4 8
}
The interesting part here is that in C++ a pointer is an iterator to an array. The STL took what was existing and build convention around it.
It there any further subtlety to this that I am missing?
|
Yes, there is a large conceptual difference. C++ utilizes different "classes" of iterators. Some are used for random access (unlike Java), some are used for forward access (like java). While even others are used for writing data (for use with, say, transform).
See the iterators concept in the C++ Documentation:
Input Iterator
Output Iterator
Forward Iterator
Bidirectional Iterator
Random Access Iterator
These are far more interesting and powerful compared to Java/C#'s puny iterators. Hopefully these conventions will be codified using C++0x's Concepts.
|
56,391 | 56,418 |
Automatically checking for a new version of my application
|
Trying to honor a feature request from our customers, I'd like that my application, when Internet is available, check on our website if a new version is available.
The problem is that I have no idea about what have to be done on the server side.
I can imagine that my application (developped in C++ using Qt) has to send a request (HTTP ?) to the server, but what is going to respond to this request ? In order to go through firewalls, I guess I'll have to use port 80 ? Is this correct ?
Or, for such a feature, do I have to ask our network admin to open a specific port number through which I'll communicate ?
@pilif : thanks for your detailed answer. There is still something which is unclear for me :
like
http://www.example.com/update?version=1.2.4
Then you can return what ever you want, probably also the download-URL of the installer of the new version.
How do I return something ? Will it be a php or asp page (I know nothing about PHP nor ASP, I have to confess) ? How can I decode the ?version=1.2.4 part in order to return something accordingly ?
|
I would absolutely recommend to just do a plain HTTP request to your website. Everything else is bound to fail.
I'd make a HTTP GET request to a certain page on your site containing the version of the local application.
like
http://www.example.com/update?version=1.2.4
Then you can return what ever you want, probably also the download-URL of the installer of the new version.
Why not just put a static file with the latest version to the server and let the client decide? Because you may want (or need) to have control over the process. Maybe 1.2 won't be compatible with the server in the future, so you want the server to force the update to 1.3, but the update from 1.2.4 to 1.2.6 could be uncritical, so you might want to present the client with an optional update.
Or you want to have a breakdown over the installed base.
Or whatever. Usually, I've learned it's best to keep as much intelligence on the server, because the server is what you have ultimate control over.
Speaking here with a bit of experience in the field, here's a small preview of what can (and will - trust me) go wrong:
Your Application will be prevented from making HTTP-Requests by the various Personal Firewall applications out there.
A considerable percentage of users won't have the needed permissions to actually get the update process going.
Even if your users have allowed the old version past their personal firewall, said tool will complain because the .EXE has changed and will recommend the user not to allow the new exe to connect (users usually comply with the wishes of their security tool here).
In managed environments, you'll be shot and hanged (not necessarily in that order) for loading executable content from the web and then actually executing it.
So to keep the damage as low as possible,
fail silently when you can't connect to the update server
before updating, make sure that you have write-permission to the install directory and warn the user if you do not, or just don't update at all.
Provide a way for administrators to turn the auto-update off.
It's no fun to do what you are about to do - especially when you deal with non technically inclined users as I had to numerous times.
|
56,424 | 80,707 |
What can cause a reduction in frame rate when upgrading a graphics card?
|
We have a two-screen DirectX application that previously ran at a consistent 60 FPS (the monitors' sync rate) using a NVIDIA 8400GS (256MB). However, when we swapped out the card for one with 512 MB of RAM the frame rate struggles to get above 40 FPS. (It only gets this high because we're using triple-buffering.) The two cards are from the same manufacturer (PNY). All other things are equal, this is a Windows XP Embedded application and we started from a fresh image for each card. The driver version number is 169.21.
The application is all 2D. I.E. just a bunch of textured quads and a whole lot of pre-rendered graphics (hence the need to upgrade the card's memory). We also have compressed animations which the CPU decodes on the fly - this involves a texture lock. The locks take forever but I've also tried having a separate system memory texture for the CPU to update and then updating the rendered texture using the device's UpdateTexture method. No overall difference in performance.
Although I've read through every FAQ I can find on the internet about DirectX performance, this is still the first time I've worked on a DirectX project so any arcane bits of knowledge you have would be useful. :)
One other thing whilst I'm on the subject; when calling Present on the swap chains it seems DirectX waits for the present to complete regardless of the fact that I'm using D3DPRESENT_DONOTWAIT in both present parameters (PresentationInterval) and the flags of the call itself. Because this is a two-screen application this is a problem as the two monitors do not appear to be genlocked, I'm working around it by running the Present calls through a threadpool. What could the underlying cause of this be?
|
Are the cards exactly the same (both GeForce 8400GS), and only the memory size differ? Quite often with different memory sizes come slightly different clock rates (i.e. your card with more memory might use slower memory!).
So the first thing to check would be GPU core & memory clock rates, using something like GPU-Z.
|
56,500 | 56,514 |
Can't access variable in C++ DLL from a C app
|
I'm stuck on a fix to a legacy Visual C++ 6 app. In the C++ DLL source I have put
extern "C" _declspec(dllexport) char* MyNewVariable = 0;
which results in MyNewVariable showing up (nicely undecorated) in the export table (as shown by dumpbin /exports blah.dll). However, I can't figure out how to declare the variable so that I can access it in a C source file. I have tried various things, including
_declspec(dllimport) char* MyNewVariable;
but that just gives me a linker error:
unresolved external symbol "__declspec(dllimport) char * MyNewVariable" (__imp_?MyNewVariable@@3PADA)
extern "C" _declspec(dllimport) char* MyNewVariable;
as suggested by Tony (and as I tried before) results in a different expected decoration, but still hasn't removed it:
unresolved external symbol __imp__MyNewVariable
How do I write the declaration so that the C++ DLL variable is accessible from the C app?
The Answer
As identified by botismarius and others (many thanks to all), I needed to link with the DLL's .lib. To prevent the name being mangled I needed to declare it (in the C source) with no decorators, which means I needed to use the .lib file.
|
you must link against the lib generated after compiling the DLL. In the linker options of the project, you must add the .lib file. And yes, you should also declare the variable as:
extern "C" { declspec(dllimport) char MyNewVariable; }
|
56,682 | 56,768 |
How to see if a subfile of a directory has changed
|
In Windows, is there an easy way to tell if a folder has a subfile that has changed?
I verified, and the last modified date on the folder does not get updated when a subfile changes.
Is there a registry entry I can set that will modify this behavior?
If it matters, I am using an NTFS volume.
I would ultimately like to have this ability from a C++ program.
Scanning an entire directory recursively will not work for me because the folder is much too large.
Update: I really need a way to do this without a process running while the change occurs. So installing a file system watcher is not optimal for me.
Update2: The archive bit will also not work because it has the same problem as the last modification date. The file's archive bit will be set, but the folders will not.
|
This article should help. Basically, you create one or more notification object such as:
HANDLE dwChangeHandles[2];
dwChangeHandles[0] = FindFirstChangeNotification(
lpDir, // directory to watch
FALSE, // do not watch subtree
FILE_NOTIFY_CHANGE_FILE_NAME); // watch file name changes
if (dwChangeHandles[0] == INVALID_HANDLE_VALUE)
{
printf("\n ERROR: FindFirstChangeNotification function failed.\n");
ExitProcess(GetLastError());
}
// Watch the subtree for directory creation and deletion.
dwChangeHandles[1] = FindFirstChangeNotification(
lpDrive, // directory to watch
TRUE, // watch the subtree
FILE_NOTIFY_CHANGE_DIR_NAME); // watch dir name changes
if (dwChangeHandles[1] == INVALID_HANDLE_VALUE)
{
printf("\n ERROR: FindFirstChangeNotification function failed.\n");
ExitProcess(GetLastError());
}
and then you wait for a notification:
while (TRUE)
{
// Wait for notification.
printf("\nWaiting for notification...\n");
DWORD dwWaitStatus = WaitForMultipleObjects(2, dwChangeHandles,
FALSE, INFINITE);
switch (dwWaitStatus)
{
case WAIT_OBJECT_0:
// A file was created, renamed, or deleted in the directory.
// Restart the notification.
if ( FindNextChangeNotification(dwChangeHandles[0]) == FALSE )
{
printf("\n ERROR: FindNextChangeNotification function failed.\n");
ExitProcess(GetLastError());
}
break;
case WAIT_OBJECT_0 + 1:
// Restart the notification.
if (FindNextChangeNotification(dwChangeHandles[1]) == FALSE )
{
printf("\n ERROR: FindNextChangeNotification function failed.\n");
ExitProcess(GetLastError());
}
break;
case WAIT_TIMEOUT:
// A time-out occurred. This would happen if some value other
// than INFINITE is used in the Wait call and no changes occur.
// In a single-threaded environment, you might not want an
// INFINITE wait.
printf("\nNo changes in the time-out period.\n");
break;
default:
printf("\n ERROR: Unhandled dwWaitStatus.\n");
ExitProcess(GetLastError());
break;
}
}
}
|
56,741 | 56,882 |
File system info - how to query it?
|
Is there a way to access file system info via some type of Windows API? If not what other methods are available to a user mode developer?
|
Not very clean, but you can use DeviceIoControl()
Open volume as a file, pass resulting handle to DeviceIoControl() together with control code. Check MSDN for control codes, there is something like "read journal record".
|
57,840 | 57,862 |
How to attach debugger to step into native (C++) code from a managed (C#) wrapper?
|
I have a wrapper around a C++ function call which I call from C# code. How do I attach a debugger in Visual Studio to step into the native C++ code?
This is the wrapper that I have which calls GetData() defined in a C++ file:
[DllImport("Unmanaged.dll", CallingConvention=CallingConvention.Cdecl,
EntryPoint = "GetData", BestFitMapping = false)]
public static extern String GetData(String url);
The code is crashing and I want to investigate the root cause.
Thanks,
Nikhil
|
Check the Debug tab on your project's properties page. There should be an "Enable unmanaged code debugging" checkbox. This worked for me when we developed a new .NET UI for our old c++ DLLs.
If your unmanaged DLL is being built from another project (for a while ours were being built using VS6) just make sure you have the DLL's pdb file handy for the debugging.
The other approach is to use the C# exe as the target exe to run from the DLL project, you can then debug your DLL normally.
|
58,058 | 58,061 |
Using C++ classes in .so libraries
|
I'm trying to write a small class library for a C++ course.
I was wondering if it was possible to define a set of classes in my shared object and then using them directly in my main program that demos the library. Are there any tricks involved? I remember reading this long ago (before I started really programming) that C++ classes only worked with MFC .dlls and not plain ones, but that's just the windows side.
|
C++ classes work fine in .so shared libraries (they also work in non-MFC DLLs on Windows, but that's not really your question). It's actually easier than Windows, because you don't have to explicitly export any symbols from the libraries.
This document will answer most of your questions: http://people.redhat.com/drepper/dsohowto.pdf
The main things to remember are to use the -fPIC option when compiling, and the -shared option when linking. You can find plenty of examples on the net.
|
58,730 | 58,737 |
Open source PDF library for C/C++ application?
|
I want to be able to generate PDF output from my (native) C++ Windows application. Are there any free/open source libraries available to do this?
I looked at the answers to this question, but they mostly relate to .Net.
|
LibHaru
Haru is a free, cross platform,
open-sourced software library for
generating PDF written in ANSI-C. It
can work as both a static-library (.a,
.lib) and a shared-library (.so,
.dll).
Didn't try it myself, but maybe it can help you
|
58,851 | 59,146 |
Can I set a breakpoint on 'memory access' in GDB?
|
I am running an application through gdb and I want to set a breakpoint for any time a specific variable is accessed / changed. Is there a good method for doing this? I would also be interested in other ways to monitor a variable in C/C++ to see if/when it changes.
|
watch only breaks on write, rwatch let you break on read, and awatch let you break on read/write.
You can set read watchpoints on memory locations:
gdb$ rwatch *0xfeedface
Hardware read watchpoint 2: *0xfeedface
but one limitation applies to the rwatch and awatch commands; you can't use gdb variables
in expressions:
gdb$ rwatch $ebx+0xec1a04f
Expression cannot be implemented with read/access watchpoint.
So you have to expand them yourself:
gdb$ print $ebx
$13 = 0x135700
gdb$ rwatch *0x135700+0xec1a04f
Hardware read watchpoint 3: *0x135700 + 0xec1a04f
gdb$ c
Hardware read watchpoint 3: *0x135700 + 0xec1a04f
Value = 0xec34daf
0x9527d6e7 in objc_msgSend ()
Edit: Oh, and by the way. You need either hardware or software support. Software is obviously much slower. To find out if your OS supports hardware watchpoints you can see the can-use-hw-watchpoints environment setting.
gdb$ show can-use-hw-watchpoints
Debugger's willingness to use watchpoint hardware is 1.
|
59,280 | 59,317 |
Programmatically change combobox
|
I need to update a combobox with a new value so it changes the reflected text in it. The cleanest way to do this is after the comboboxhas been initialised and with a message.
So I am trying to craft a postmessage to the hwnd that contains the combobox.
So if I want to send a message to it, changing the currently selected item to the nth item, what would the postmessage look like?
I am guessing that it would involve ON_CBN_SELCHANGE, but I can't get it to work right.
|
You want ComboBox_SetCurSel:
ComboBox_SetCurSel(hWndCombo, n);
or if it's an MFC CComboBox control you can probably do:
m_combo.SetCurSel(2);
I would imagine if you're doing it manually you would also want SendMessage rather than PostMessage. CBN_SELCHANGE is the notification that the control sends back to you when the selection is changed.
Finally, you might want to add the c++ tag to this question.
|
59,635 | 70,808 |
App does not run with VS 2008 SP1 DLLs, previous version works with RTM versions
|
Since our switch from Visual Studio 6 to Visual Studio 2008, we've been using the MFC90.dll and msvc[pr]90.dlls along with the manifest files in a private side-by-side configuration so as to not worry about versions or installing them to the system.
Pre-SP1, this was working fine (and still works fine on our developer machines). Now that we've done some testing post-SP1 I've been pulling my hair out since yesterday morning.
First off, our NSIS installer script pulls the dlls and manifest files from the redist folder. These were no longer correct, as the app still links to the RTM version.
So I added the define for _BIND_TO_CURRENT_VCLIBS_VERSION=1 to all of our projects so that they will use the SP1 DLLs in the redist folder (or subsequent ones as new service packs come out). It took me hours to find this.
I've double checked the generated manifest files in the intermediate files folder from the compilation, and they correctly list the 9.0.30729.1 SP1 versions. I've double and triple checked depends on a clean machine: it all links to the local dlls with no errors.
Running the app still gets the following error:
The application failed to initialize properly (0xc0150002). Click on OK to terminate the application.
None of the searches I've done on google or microsoft have come up with anything that relates to my specific issues (but there are hits back to 2005 with this error message).
Any one had any similar problem with SP1?
Options:
Find the problem and fix it so it works as it should (preferred)
Install the redist
dig out the old RTM dlls and manifest files and remove the #define to use the current ones. (I've got them in an earlier installer build, since Microsoft blasts them out of your redist folder!)
Edit: I've tried re-building with the define turned off (link to RTM dlls), and that works as long as the RTM dlls are installed in the folder. If the SP1 dlls are dropped in, it gets the following error:
c:\Program Files\...\...\X.exe
This application has failed to start because the application configuration is incorrect. Reinstalling the application may fix this problem.
Has no-one else had to deal with this issue?
Edit: Just for grins, I downloaded and ran the vcredist_x86.exe for VS2008SP1 on my test machine. It works. With the SP1 DLLs. And my RTM linked app. But NOT in a private side-by-side distribution that worked pre-SP1.
|
I have battled this problem myself last week and consider myself somewhat of an expert now ;)
I'm 99% sure that not all dlls and static libraries were recompiled with the SP1 version. You need to put
#define _BIND_TO_CURRENT_MFC_VERSION 1
#define _BIND_TO_CURRENT_CRT_VERSION 1
into every project you're using. For every project of a real-world size, it's very easy to forget some small lib that wasn't recompiled.
There are more flags that define what versions to bind to; it's documented on http://msdn.microsoft.com/en-us/library/cc664727%28v=vs.90%29.aspx . As an alternative to the lines above, you can also put
#define _BIND_TO_CURRENT_VCLIBS_VERSION 1
which will bind to the latest version of all VC libs (CRT, MFC, ATL, OpenMP).
Then, check what the embedded manifest says. Download XM Resource Editor: http://www.wilsonc.demon.co.uk/d10resourceeditor.htm. Open every dll and exe in your solution. Look under 'XP Theme Manifest'. Check that the 'version' attribute on the right-hand side is '9.0.30729.1'. If it's '9.0.21022', some static library is pulling in the manifest for the old version.
What I found is that in many cases, both versions were included in the manifest. This means that some libraries use the sp1 version and others don't.
A great way to debug which libraries don't have the preprocessor directives set: temporarily modify your platform headers so that compilation stops when it tries to embed the old manifest. Open C:\Program Files\Microsoft Visual Studio 9.0\VC\crt\include\crtassem.h. Search for the '21022' string. In that define, put something invalid (change 'define' to 'blehbleh' or so). This way, when you're compiling a project where the _BIND_TO_CURRENT_CRT_VERSION preprocessor flag is not set, your compilation will stop and you'll know that you need to add them or made sure that it's applied everywhere.
Also make sure to use Dependency Walker so that you know what dlls are being pulled in. It's easiest to install a fresh Windows XP copy with no updates (only SP2) on a virtual machine. This way you know for sure that there is nothing in the SxS folder that is being used instead of the side-by-side dlls that you supplied.
|
59,670 | 59,687 |
How to get rid of `deprecated conversion from string constant to ‘char*’` warnings in GCC
|
I'm working on an exceedingly large codebase, and recently upgraded to GCC 4.3, which now triggers this warning:
warning: deprecated conversion from string constant to ‘char*’
Obviously, the correct way to fix this is to find every declaration like
char *s = "constant string";
or function call like:
void foo(char *s);
foo("constant string");
and make them const char pointers. However, that would mean touching 564 files, minimum, which is not a task I wish to perform at this point in time. The problem right now is that I'm running with -Werror, so I need some way to stifle these warnings. How can I do that?
|
I believe passing -Wno-write-strings to GCC will suppress this warning.
|
60,000 | 2,688,631 |
C++ inheritance and member function pointers
|
In C++, can member function pointers be used to point to derived (or even base) class members?
EDIT:
Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance.
Y therefore has a base class X and a derived class Z.
Now we can define a member function pointer p for class Y. This is written as:
void (Y::*p)();
(For simplicity, I'll assume we're only interested in functions with the signature void f() )
This pointer p can now be used to point to member functions of class Y.
This question (two questions, really) is then:
Can p be used to point to a function in the derived class Z?
Can p be used to point to a function in the base class X?
|
C++03 std, §4.11 2 Pointer to member conversions:
An rvalue of type “pointer to member of B of type cv T,” where B is a class type, can be converted to an rvalue of type “pointer to member of D of type cv T,” where D is a derived class (clause 10) of B. If B is an inaccessible (clause 11), ambiguous (10.2) or virtual (10.1) base class of D, a program that necessitates this conversion is ill-formed. The result of the conversion refers to the same member as the pointer to member before the conversion took place, but it refers to the base class member as if it were a member of the derived class. The result refers to the member in D’s instance of B. Since the result has type “pointer to member of D of type cv T,” it can be dereferenced with a D object. The result is the same as if the pointer to member of B were dereferenced with the B sub-object of D. The null member pointer value is converted to the null member pointer value of the destination type. 52)
52)The rule for conversion of pointers to members (from pointer to member of base to pointer to member of derived) appears inverted compared to the rule for pointers to objects (from pointer to derived to pointer to base) (4.10, clause 10). This inversion is necessary to ensure type safety. Note that a pointer to member is not a pointer to object or a pointer to function and the rules for conversions of such pointers do not apply to pointers to members. In particular, a pointer to member cannot be converted to a void*.
In short, you can convert a pointer to a member of an accessible, non-virtual base class to a pointer to a member of a derived class as long as the member isn't ambiguous.
class A {
public:
void foo();
};
class B : public A {};
class C {
public:
void bar();
};
class D {
public:
void baz();
};
class E : public A, public B, private C, public virtual D {
public:
typedef void (E::*member)();
};
class F:public E {
public:
void bam();
};
...
int main() {
E::member mbr;
mbr = &A::foo; // invalid: ambiguous; E's A or B's A?
mbr = &C::bar; // invalid: C is private
mbr = &D::baz; // invalid: D is virtual
mbr = &F::bam; // invalid: conversion isn't defined by the standard
...
Conversion in the other direction (via static_cast) is governed by § 5.2.9 9:
An rvalue of type "pointer to member of D of type cv1 T" can be converted to an rvalue of type "pointer to member of B of type cv2 T", where B is a base class (clause 10 class.derived) of D, if a valid standard conversion from "pointer to member of B of type T" to "pointer to member of D of type T" exists (4.11 conv.mem), and cv2 is the same cv-qualification as, or greater cv-qualification than, cv1.11) The null member pointer value (4.11 conv.mem) is converted to the null member pointer value of the destination type. If class B contains the original member, or is a base or derived class of the class containing the original member, the resulting pointer to member points to the original member. Otherwise, the result of the cast is undefined. [Note: although class B need not contain the original member, the dynamic type of the object on which the pointer to member is dereferenced must contain the original member; see 5.5 expr.mptr.oper.]
11) Function types (including those used in pointer to member function
types) are never cv-qualified; see 8.3.5 dcl.fct.
In short, you can convert from a derived D::* to a base B::* if you can convert from a B::* to a D::*, though you can only use the B::* on objects that are of type D or are descended from D.
|
60,331 | 60,355 |
C++ Quiz - Singletons
|
I'll soon be posting an article on my blog, but I'd like to verify I haven't missed anything first.
Find an example I've missed, and I'll cite you on my post.
The topic is failed Singleton implementations: In what cases can you accidentally get multiple instances of a singleton?
So far, I've come up with:
Race Condition on first call to instance()
Incorporation into multiple DLLs or DLL and executable
Template definition of a singleton - actually separate classes
Any other ways I'm missing - perhaps with inheritance?
|
If you use a static instance field that you initialize in your cpp file, you can get multiple instances (and even worse behavior) if the initialization of some static/global tries to get an instance of your singleton. This is because the order of static initialization across compilation units is undefined.
|
60,422 | 930,781 |
IDebugProgramProvider2.GetProviderProcessData on Vista
|
As part of a JavaScript Profiler for IE 6/7 I needed to load a custom debugger that I created into IE. I got this working fine on XP, but couldn't get it working on Vista (full story here: http://damianblog.com/2008/09/09/tracejs-v2-rip/).
The call to GetProviderProcessData is failing on Vista. Anyone have any suggestions?
Thanks,
Damian
// Create the MsProgramProvider
IDebugProgramProvider2* pIDebugProgramProvider2 = 0;
HRESULT st = CoCreateInstance(CLSID_MsProgramProvider, 0, CLSCTX_ALL, IID_IDebugProgramProvider2, (void**)&pIDebugProgramProvider2);
if(st != S_OK) {
return st;
}
// Get the IDebugProgramNode2 instances running in this process
AD_PROCESS_ID processID;
processID.ProcessId.dwProcessId = GetCurrentProcessId();
processID.ProcessIdType = AD_PROCESS_ID_SYSTEM;
CONST_GUID_ARRAY engineFilter;
engineFilter.dwCount = 0;
PROVIDER_PROCESS_DATA processData;
st = pIDebugProgramProvider2->GetProviderProcessData(PFLAG_GET_PROGRAM_NODES|PFLAG_DEBUGGEE, 0, processID, engineFilter, &processData);
if(st != S_OK) {
ShowError(L"GPPD Failed", st);
pIDebugProgramProvider2->Release();
return st;
}
|
It would help to know what the error result was.
Possible problems I can think of:
If your getting permission denied, your most likely missing some requried Privilege in your ACL. New ones are sometimes not doceumented well, check the latest Platform SDK headers to see if any new ones that still out. It may be that under vista the Privilege is not assigned my default to your ACL any longer.
If your getting some sort of Not Found type error, then it may be 32bit / 64bit problem. Your debbugging API may only be available under 64bit COM on vista 64. The 32bit/64bit interoperation can be very confusing.
|
60,507 | 60,513 |
C++ function pointers and classes
|
Say I have:
void Render(void(*Call)())
{
D3dDevice->BeginScene();
Call();
D3dDevice->EndScene();
D3dDevice->Present(0,0,0,0);
}
This is fine as long as the function I want to use to render is a function or a static member function:
Render(MainMenuRender);
Render(MainMenu::Render);
However, I really want to be able to use a class method as well since in most cases the rendering function will want to access member variables, and Id rather not make the class instance global, e.g.
Render(MainMenu->Render);
However I really have no idea how to do this, and still allow functions and static member functions to be used.
|
There are a lot of ways to skin this cat, including templates. My favorite is Boost.function as I've found it to be the most flexible in the long run. Also read up on Boost.bind for binding to member functions as well as many other tricks.
It would look like this:
#include <boost/bind.hpp>
#include <boost/function.hpp>
void Render(boost::function0<void> Call)
{
// as before...
}
Render(boost::bind(&MainMenu::Render, myMainMenuInstance));
|
60,570 | 60,605 |
Why should the "PIMPL" idiom be used?
|
Backgrounder:
The PIMPL Idiom (Pointer to IMPLementation) is a technique for implementation hiding in which a public class wraps a structure or class that cannot be seen outside the library the public class is part of.
This hides internal implementation details and data from the user of the library.
When implementing this idiom why would you place the public methods on the pimpl class and not the public class since the public classes method implementations would be compiled into the library and the user only has the header file?
To illustrate, this code puts the Purr() implementation on the impl class and wraps it as well.
Why not implement Purr directly on the public class?
// header file:
class Cat {
private:
class CatImpl; // Not defined here
CatImpl *cat_; // Handle
public:
Cat(); // Constructor
~Cat(); // Destructor
// Other operations...
Purr();
};
// CPP file:
#include "cat.h"
class Cat::CatImpl {
Purr();
... // The actual implementation can be anything
};
Cat::Cat() {
cat_ = new CatImpl;
}
Cat::~Cat() {
delete cat_;
}
Cat::Purr(){ cat_->Purr(); }
CatImpl::Purr(){
printf("purrrrrr");
}
|
Because you want Purr() to be able to use private members of CatImpl. Cat::Purr() would not be allowed such an access without a friend declaration.
Because you then don't mix responsibilities: one class implements, one class forwards.
|
60,641 | 60,691 |
How to replace WinAPI functions calls in the MS VC++ project with my own implementation (name and parameters set are the same)?
|
I need to replace all WinAPI calls of the
CreateFile,
ReadFile,
SetFilePointer,
CloseHandle
with my own implementation (which use low-level file reading via Bluetooth).
The code, where functions will be replaced, is Video File Player and it already works with the regular hdd files.
It is also needed, that Video Player still can play files from HDD, if the file in the VideoPlayer input is a regular hdd file.
What is the best practice for such task?
|
I suggest that you follow these steps:
Write a set of wrapper functions, e.g MyCreateFile, MyReadFile, etc, that initially just call the corresponding API and pass the same arguments along, unmodified.
Use your text editor to search for all calls to the original APIs, and replace these with calls to your new wrapper functions.
Test that the application still functions correctly.
Modify the wrapper functions to suit your own purposes.
Note that CreateFile is a macro which expands to either CreateFileW or CreateFileA, depending on whether UNICODE is defined. Consider using LPCTSTR and the TCHAR functions so that your application can be built as either ANSI or Unicode.
Please don't use #define, as suggested in other responses here, as this will just lead to maintenance problems, and as Maximilian correctly points out, it's not a best-practice.
|
60,653 | 60,655 |
Is global memory initialized in C++?
|
Is global memory initialized in C++? And if so, how?
(Second) clarification:
When a program starts up, what is in the memory space which will become global memory, prior to primitives being initialized? I'm trying to understand if it is zeroed out, or garbage for example.
The situation is: can a singleton reference be set - via an instance() call, prior to its initialization:
MySingleton* MySingleton::_instance = NULL;
and get two singleton instances as a result?
See my C++ quiz on on multiple instances of a singleton...
|
Yes global primitives are initialized to NULL.
Example:
int x;
int main(int argc, char**argv)
{
assert(x == 0);
int y;
//assert(y == 0); <-- wrong can't assume this.
}
You cannot make any assumptions about classes, structs, arrays, blocks of memory on the heap...
It's safest just to always initialize everything.
|
60,673 | 60,712 |
Guidelines to improve your code
|
What guidelines do you follow to improve the general quality of your code? Many people have rules about how to write C++ code that (supposedly) make it harder to make mistakes. I've seen people insist that every if statement is followed by a brace block ({...}).
I'm interested in what guidelines other people follow, and the reasons behind them. I'm also interested in guidelines that you think are rubbish, but are commonly held. Can anyone suggest a few?
To get the ball rolling, I'll mention a few to start with:
Always use braces after every if / else statement (mentioned above). The rationale behind this is that it's not always easy to tell if a single statement is actually one statement, or a preprocessor macro that expands to more than one statement, so this code would break:
// top of file:
#define statement doSomething(); doSomethingElse
// in implementation:
if (somecondition)
doSomething();
but if you use braces then it will work as expected.
Use preprocessor macros for conditional compilation ONLY. preprocessor macros can cause all sorts of hell, since they don't allow C++ scoping rules. I've run aground many times due to preprocessor macros with common names in header files. If you're not careful you can cause all sorts of havoc!
Now over to you.
|
A few of my personal favorites:
Strive to write code that is const correct. You will enlist the compiler to help weed out easy to fix but sometimes painful bugs. Your code will also tell a story of what you had in mind at the time you wrote it -- valuable for newcomers or maintainers once you're gone.
Get out of the memory management business. Learn to use smart pointers: std::auto_ptr, std::tr1::shared_ptr (or boost::shared_ptr) and boost::scoped_ptr. Learn the differences between them and when to use one vs. another.
You're probably going to be using the Standard Template Library. Read the Josuttis book. Don't just stop after the first few chapters on containers thinking that you know the STL. Push through to the good stuff: algorithms and function objects.
|
60,751 | 60,790 |
c++ Having multiple graphics options
|
Currently my app uses just Direct3D9 for graphics, however in the future I' m planning to extend this to D3D10 and possibly OpenGL. The question is how can I do this in a tidy way?
At present there are various Render methods in my code
void Render(boost::function<void()> &Call)
{
D3dDevice->BeginScene();
Call();
D3dDevice->EndScene();
D3dDevice->Present(0,0,0,0);
}
The function passed then depends on the exact state, eg MainMenu->Render, Loading->Render, etc. These will then oftern call the methods of other objects.
void RenderGame()
{
for(entity::iterator it = entity::instances.begin();it != entity::instance.end(); ++it)
(*it)->Render();
UI->Render();
}
And a sample class derived from entity::Base
class Sprite: public Base
{
IDirect3DTexture9 *Tex;
Point2 Pos;
Size2 Size;
public:
Sprite(IDirect3DTexture9 *Tex, const Point2 &Pos, const Size2 &Size);
virtual void Render();
};
Each method then takes care of how best to render given the more detailed settings (eg are pixel shaders supported or not).
The problem is I'm really not sure how to extend this to be able to use one of, what may be somewhat different (D3D v OpenGL) render modes...
|
Define an interface that is sufficient for your application's graphic output demands. Then implement this interface for every renderer you want to support.
class IRenderer {
public:
virtual ~IRenderer() {}
virtual void RenderModel(CModel* model) = 0;
virtual void DrawScreenQuad(int x1, int y1, int x2, int y2) = 0;
// ...etc...
};
class COpenGLRenderer : public IRenderer {
public:
virtual void RenderModel(CModel* model) {
// render model using OpenGL
}
virtual void DrawScreenQuad(int x1, int y1, int x2, int y2) {
// draw screen aligned quad using OpenGL
}
};
class CDirect3DRenderer : public IRenderer {
// similar, but render using Direct3D
};
Properly designing and maintaining these interfaces can be very challenging though.
In case you also operate with render driver dependent objects like textures, you can use a factory pattern to have the separate renderers each create their own implementation of e.g. ITexture using a factory method in IRenderer:
class IRenderer {
//...
virtual ITexture* CreateTexture(const char* filename) = 0;
//...
};
class COpenGLRenderer : public IRenderer {
//...
virtual ITexture* CreateTexture(const char* filename) {
// COpenGLTexture is the OpenGL specific ITexture implementation
return new COpenGLTexture(filename);
}
//...
};
Isn't it an idea to look at existing (3d) engines though? In my experience designing this kind of interfaces really distracts from what you actually want to make :)
|
60,830 | 60,850 |
What is wrong with using inline functions?
|
While it would be very convenient to use inline functions at some situations,
Are there any drawbacks with inline functions?
Conclusion:
Apparently, There is nothing wrong with using inline functions.
But it is worth noting the following points!
Overuse of inlining can actually make programs slower. Depending on a function's size, inlining it can cause the code size to increase or decrease. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size. On modern processors smaller code usually runs faster due to better use of the instruction cache. - Google Guidelines
The speed benefits of inline functions tend to diminish as the function grows in size. At some point the overhead of the function call becomes small compared to the execution of the function body, and the benefit is lost - Source
There are few situations where an inline function may not work:
For a function returning values; if a return statement exists.
For a function not returning any values; if a loop, switch or goto statement exists.
If a function is recursive. -Source
The __inline keyword causes a function to be inlined only if you specify the optimize option. If optimize is specified, whether or not __inline is honored depends on the setting of the inline optimizer option. By default, the inline option is in effect whenever the optimizer is run. If you specify optimize , you must also specify the noinline option if you want the __inline keyword to be ignored. -Source
|
It worth pointing out that the inline keyword is actually just a hint to the compiler. The compiler may ignore the inline and simply generate code for the function someplace.
The main drawback to inline functions is that it can increase the size of your executable (depending on the number of instantiations). This can be a problem on some platforms (eg. embedded systems), especially if the function itself is recursive.
I'd also recommend making inline'd functions very small - The speed benefits of inline functions tend to diminish as the function grows in size. At some point the overhead of the function call becomes small compared to the execution of the function body, and the benefit is lost.
|
60,871 | 61,061 |
How to solve Memory Fragmentation
|
We've occasionally been getting problems whereby our long-running server processes (running on Windows Server 2003) have thrown an exception due to a memory allocation failure. Our suspicion is these allocations are failing due to memory fragmentation.
Therefore, we've been looking at some alternative memory allocation mechanisms that may help us and I'm hoping someone can tell me the best one:
1) Use Windows Low-fragmentation Heap
2) jemalloc - as used in Firefox 3
3) Doug Lea's malloc
Our server process is developed using cross-platform C++ code, so any solution would be ideally cross-platform also (do *nix operating systems suffer from this type of memory fragmentation?).
Also, am I right in thinking that LFH is now the default memory allocation mechanism for Windows Server 2008 / Vista?... Will my current problems "go away" if our customers simply upgrade their server os?
|
First, I agree with the other posters who suggested a resource leak. You really want to rule that out first.
Hopefully, the heap manager you are currently using has a way to dump out the actual total free space available in the heap (across all free blocks) and also the total number of blocks that it is divided over. If the average free block size is relatively small compared to the total free space in the heap, then you do have a fragmentation problem. Alternatively, if you can dump the size of the largest free block and compare that to the total free space, that will accomplish the same thing. The largest free block would be small relative to the total free space available across all blocks if you are running into fragmentation.
To be very clear about the above, in all cases we are talking about free blocks in the heap, not the allocated blocks in the heap. In any case, if the above conditions are not met, then you do have a leak situation of some sort.
So, once you have ruled out a leak, you could consider using a better allocator. Doug Lea's malloc suggested in the question is a very good allocator for general use applications and very robust most of the time. Put another way, it has been time tested to work very well for most any application. However, no algorithm is ideal for all applications and any management algorithm approach can be broken by the right pathelogical conditions against it's design.
Why are you having a fragmentation problem? - Sources of fragmentation problems are caused by the behavior of an application and have to do with greatly different allocation lifetimes in the same memory arena. That is, some objects are allocated and freed regularly while other types of objects persist for extended periods of time all in the same heap.....think of the longer lifetime ones as poking holes into larger areas of the arena and thereby preventing the coalesce of adjacent blocks that have been freed.
To address this type of problem, the best thing you can do is logically divide the heap into sub arenas where the lifetimes are more similar. In effect, you want a transient heap and a persistent heap or heaps that group things of similar lifetimes.
Some others have suggested another approach to solve the problem which is to attempt to make the allocation sizes more similar or identical, but this is less ideal because it creates a different type of fragmentation called internal fragmentation - which is in effect the wasted space you have by allocating more memory in the block than you need.
Additionally, with a good heap allocator, like Doug Lea's, making the block sizes more similar is unnecessary because the allocator will already be doing a power of two size bucketing scheme that will make it completely unnecessary to artificially adjust the allocation sizes passed to malloc() - in effect, his heap manager does that for you automatically much more robustly than the application will be able to make adjustments.
|
60,977 | 61,105 |
Resetting detection of source file changes
|
Sometimes I have to work on code that moves the computer clock forward. In this case some .cpp or .h files get their latest modification date set to the future time.
Later on, when my clock is fixed, and I compile my sources, system rebuilds most of the project because some of the latest modification dates are in the future. Each subsequent recompile has the same problem.
Solution that I know are:
a) Find the file that has the future time and re-save it. This method is not ideal because the project is very big and it takes time even for windows advanced search to find the files that are changed.
b) Delete the whole project and re-check it out from svn.
Does anyone know how I can get around this problem?
Is there perhaps a setting in visual studio that will allow me to tell the compiler to use the archive bit instead of the last modification date to detect source file changes?
Or perhaps there is a recursive modification date reset tool that can be used in this situation?
|
If this was my problem, I'd look for ways to avoid mucking with the system time. Isolating the code under unit tests, or a virtual machine, or something.
However, because I love PowerShell:
Get-ChildItem -r . |
? { $_.LastWriteTime -gt ([DateTime]::Now) } |
Set-ItemProperty -Name "LastWriteTime" -Value ([DateTime]::Now)
|
61,071 | 61,148 |
How do I disassemble a VC++ application?
|
I believe the application has some parts that target .NET, and some that don't. I'm particularly interested in looking at the resource files, if there are any.
|
To add to aku's excellent answer, for English speakers, IDA Pro is available at http://www.hex-rays.com/.
|
61,253 | 61,283 |
How to be notified of file/directory change in C/C++, ideally using POSIX
|
The subject says it all - normally easy and cross platform way is to poll, intelligently. But every OS has some means to notify without polling. Is it possible in a reasonably cross platform way? (I only really care about Windows and Linux, but I use mac, so I thought posix may help?)
|
Linux users can use inotify
inotify is a Linux kernel subsystem
that provides file system event
notification.
Some goodies for Windows fellows:
File Change Notification on MSDN
"When Folders Change" article
File System Notification on Change
|
61,278 | 61,279 |
Quick and dirty way to profile your code
|
What method do you use when you want to get performance data about specific code paths?
|
This method has several limitations, but I still find it very useful. I'll list the limitations (I know of) up front and let whoever wants to use it do so at their own risk.
The original version I posted over-reported time spent in recursive calls (as pointed out in the comments to the answer).
It's not thread safe, it wasn't thread safe before I added the code to ignore recursion and it's even less thread safe now.
Although it's very efficient if it's called many times (millions), it will have a measurable effect on the outcome so that scopes you measure will take longer than those you don't.
I use this class when the problem at hand doesn't justify profiling all my code or I get some data from a profiler that I want to verify. Basically it sums up the time you spent in a specific block and at the end of the program outputs it to the debug stream (viewable with DbgView), including how many times the code was executed (and the average time spent of course)).
#pragma once
#include <tchar.h>
#include <windows.h>
#include <sstream>
#include <boost/noncopyable.hpp>
namespace scope_timer {
class time_collector : boost::noncopyable {
__int64 total;
LARGE_INTEGER start;
size_t times;
const TCHAR* name;
double cpu_frequency()
{ // cache the CPU frequency, which doesn't change.
static double ret = 0; // store as double so devision later on is floating point and not truncating
if (ret == 0) {
LARGE_INTEGER freq;
QueryPerformanceFrequency(&freq);
ret = static_cast<double>(freq.QuadPart);
}
return ret;
}
bool in_use;
public:
time_collector(const TCHAR* n)
: times(0)
, name(n)
, total(0)
, start(LARGE_INTEGER())
, in_use(false)
{
}
~time_collector()
{
std::basic_ostringstream<TCHAR> msg;
msg << _T("scope_timer> ") << name << _T(" called: ");
double seconds = total / cpu_frequency();
double average = seconds / times;
msg << times << _T(" times total time: ") << seconds << _T(" seconds ")
<< _T(" (avg ") << average <<_T(")\n");
OutputDebugString(msg.str().c_str());
}
void add_time(__int64 ticks)
{
total += ticks;
++times;
in_use = false;
}
bool aquire()
{
if (in_use)
return false;
in_use = true;
return true;
}
};
class one_time : boost::noncopyable {
LARGE_INTEGER start;
time_collector* collector;
public:
one_time(time_collector& tc)
{
if (tc.aquire()) {
collector = &tc;
QueryPerformanceCounter(&start);
}
else
collector = 0;
}
~one_time()
{
if (collector) {
LARGE_INTEGER end;
QueryPerformanceCounter(&end);
collector->add_time(end.QuadPart - start.QuadPart);
}
}
};
}
// Usage TIME_THIS_SCOPE(XX); where XX is a C variable name (can begin with a number)
#define TIME_THIS_SCOPE(name) \
static scope_timer::time_collector st_time_collector_##name(_T(#name)); \
scope_timer::one_time st_one_time_##name(st_time_collector_##name)
|
61,402 | 61,435 |
C++ Exception code lookup
|
Knowing an exception code, is there a way to find out more about what the actual exception that was thrown means?
My exception in question:
0x64487347
Exception address: 0x1
The call stack shows no information.
I'm reviewing a .dmp of a crash and not actually debugging in Visual Studio.
|
Because you're reviewing a crash dump I'll assume it came in from a customer and you cannot easily reproduce the fault with more instrumentation.
I don't have much help to offer save to note that the exception code 0x64487347 is ASCII "dShG", and developers often use the initials of the routine or fault condition when making up magic numbers like this.
A little Googling turned up one hit for dHsg in the proper context, the name of a function in a Google Book search for "Using Visual C++ 6" By Kate Gregory. Unfortunately that alone was not helpful.
|
61,669 | 61,681 |
Profiling in Visual Studio 2008 PRO
|
How do I use the profiler in Visual Studio 2008?
I know theres a build option in Config Properties -> Linker -> Advanced -> Profile (/PROFILE), however I can't find anything about actauly using it, only articles I was able to find appear to only apply to older versions of Visual Studio (eg most say to goto Build->Profile to bring up the profile dialog box, yet in 2008 there is no such menu item).
Is this because Visual Studio 2008 does not include a profiler, and if it does where is it and where is the documentation for it?
|
The profiler is only available in the Team System editions of Visual Studio 2008. The last version that I used that included a profiler was Visual C++ 6.0.
For Visual Studio 2005, you could try Compuware DevPartner Performance Analysis Community Edition.
|
61,680 | 61,684 |
How to work around a very large 2d array in C++
|
I need to create a 2D int array of size 800x800. But doing so creates a stack overflow (ha ha).
I'm new to C++, so should I do something like a vector of vectors? And just encapsulate the 2d array into a class?
Specifically, this array is my zbuffer in a graphics program. I need to store a z value for every pixel on the screen (hence the large size of 800x800).
Thanks!
|
You need about 2.5 megs, so just using the heap should be fine. You don't need a vector unless you need to resize it. See C++ FAQ Lite for an example of using a "2D" heap array.
int *array = new int[800*800];
(Don't forget to delete[] it when you're done.)
|
61,914 | 62,239 |
VS 2005 Toolbox kind of control .NET
|
I'm looking for a control that the Visual Studio "Toolbox" menu uses. It can be docked and can retract (pin).
Would you know where I can find a control or COM I could use which would look like this?
|
I would recommend the DockPanel Suite by Weifen Luo.
|
62,340 | 62,522 |
Does pop_back() really invalidate *all* iterators on an std::vector?
|
std::vector<int> ints;
// ... fill ints with random values
for(std::vector<int>::iterator it = ints.begin(); it != ints.end(); )
{
if(*it < 10)
{
*it = ints.back();
ints.pop_back();
continue;
}
it++;
}
This code is not working because when pop_back() is called, it is invalidated. But I don't find any doc talking about invalidation of iterators in std::vector::pop_back().
Do you have some links about that?
|
The call to pop_back() removes the last element in the vector and so the iterator to that element is invalidated. The pop_back() call does not invalidate iterators to items before the last element, only reallocation will do that. From Josuttis' "C++ Standard Library Reference":
Inserting or removing elements
invalidates references, pointers, and
iterators that refer to the following
element. If an insertion causes
reallocation, it invalidates all
references, iterators, and pointers.
|
62,389 | 62,416 |
What are the differences between Visual C++ 6.0 and Visual C++ 2008?
|
What are the advantages/disadvantages between MS VS C++ 6.0 and MSVS C++ 2008?
The main reason for asking such a question is that there are still many decent programmers that prefer using the older version instead of the newest version.
Is there any reason the might prefer the older over the new?
|
Well, for one thing it may be because the executables built with MSVS 6 require only msvcrt.dll (C runtime) which is shipped with Windows now.
The MSVS 2008 executables need msvcrt9 shipped with them (or already installed).
Plus, you have a lot of OSS libraries already compiled for Windows 32 bit with the 6.0 C runtime, while for the 2008 C runtime you have to take the source and compile them yourself.
(most of those libraries are actually compiled with MinGW, which too uses the 6.0 C runtime - maybe that's another reason).
|
62,501 | 62,560 |
Remote installing of windows service
|
I need to remotely install windows service on number of computers, so I use CreateService() and other service functions from winapi. I know admin password and user name for machines that I need access to. In order to gain access to remote machine I impersonate calling process with help of LogonUser like this:
//all variables are initialized correctly
int status = 0;
status = LogonUser(lpwUsername,
lpwDomain,
lpwPassword,
LOGON32_LOGON_NEW_CREDENTIALS,
LOGON32_PROVIDER_DEFAULT,
&hToken);
if (status == 0)
{
//here comes a error
}
status = ImpersonateLoggedOnUser(hToken);
if (status == 0)
{
//once again a error
}
//ok, now we are impersonated, do all service work there
So, I gain access to machine in a domain, but some of computers are out of domain. On machines that are out of domain this code doesn't work. Is there any way to access service manager on machine out of domain?
|
You can do it , the account needs to exist on the remote machine and you need to use the machine name for the domain name in the LogonUser call.
|
62,512 | 62,532 |
Three dimensional arrays of integers in C++
|
I would like to find out safe ways of implementing three dimensional arrays of integers in C++, using pointer arithmetic / dynamic memory allocation, or, alternatively using STL techniques such as vectors.
Essentially I want my integer array dimensions to look like:
[ x ][ y ][ z ]
x and y are in the range 20-6000
z is known and equals 4.
|
Have a look at the Boost multi-dimensional array library. Here's an example (adapted from the Boost documentation):
#include "boost/multi_array.hpp"
int main() {
// Create a 3D array that is 20 x 30 x 4
int x = 20;
int y = 30;
int z = 4;
typedef boost::multi_array<int, 3> array_type;
typedef array_type::index index;
array_type my_array(boost::extents[x][y][z]);
// Assign values to the elements
int values = 0;
for (index i = 0; i != x; ++i) {
for (index j = 0; j != y; ++j) {
for (index k = 0; k != z; ++k) {
my_array[i][j][k] = values++;
}
}
}
}
|
62,623 | 63,667 |
Does every Linux distro ship with gcc/g++ 4.* these days?
|
I'm considering dumping boost as a dependency... atm the only thing that I really need is shared_ptr<>, and I can get that from std::tr1, available in gcc suite 4.*
|
AFAIK, all of the distros package V 4.+ nowadays.
|
62,810 | 132,553 |
Exceptions not passed correctly thru RCF (using Boost.Serialization)
|
I use RCF with boost.serialization (why use RCF's copy when we already use the original?) It works OK, but when an exception is thrown in the server, it's not passed correctly to the client. Instead, I get an RCF::SerializationException quoting an archive_exception saying "class name too long". When I change the protocol to BsText, the exceptions is "unregistered class". When I change the protocol to SfBinary, it works.
I've registered RemoteException on both server and client like this:
BOOST_CLASS_VERSION(RCF::RemoteException, 0)
BOOST_CLASS_EXPORT(RCF::RemoteException)
I even tried serializing and deserializing a boost::shared_ptr<RCF::RemoteException> in the same test, and it works.
So how can I make RCF pass exceptions correctly without resorting to SF?
|
Here's a patch given by Jarl at CodeProject:
In RcfServer.cpp, before the line where RcfServer::handleSession() is defined (around line 792), insert the following code:
void serialize(SerializationProtocolOut & out, const RemoteException & e)
{
serialize(out, std::auto_ptr<RemoteException>(new RemoteException(e)));
}
And in Marshal.cpp, around line 37, replace this line:
ar & boost::serialization::make_nvp("Dummy", apt.get());
, with
T *pt = apt.get();
ar & boost::serialization::make_nvp("Dummy", pt);
|
62,832 | 62,843 |
Reading data from a log file as a separate application is writing to it
|
I would like to monitor a log file that is being written to by an application. I want to process the file line by line as, or shortly after, it is written. I have not found a way of detecting that a file has been extended after reaching eof.
The code needs to work on Mac and PC, and can be in any language, though I am most familiar with C++ and Perl.
Does anybody have a suggestion for the best way to do it?
|
In Perl, the File::Tail module does exactly what you need.
|
62,918 | 74,675 |
Using GCC from within VS 2005(8) IDE
|
Is there a way to utilise the GCC compiler whilst still being able to develop via the Visual Studio IDE?
Our project is cross-platform, and I quite frequently get into trouble from my colleague because I'm checking in code that's not standards compliant (this can be attributed to the VS compiler!).
I'd still like to be able to compile using the MS compiler, so I can continue debugging, etc, however I'd like to be able to switch to compile using GCC, just so that I can be sure I'm not breaking the build on other platforms.
Is this possible?
|
What I am about to suggest would still require a makefile, so I am partially repeating the advice from an earlier reply. Or, as was also mentioned earlier, maybe you already have a makefile, in which case you will have even fewer steps in order to accomplish what I am about to describe.
Once you know your specific windows command-line command for invoking make or g++ on your code, then you create a "Pre-Build Event" in your Visual Studio Project. ("Project Properties >> Configuration Properties >> Build Events >> Pre-Build Event").
The pre-build event can call a bat file script, or any other script on your machine, and that script will be able to return an error-code. Essentially, "script OK," or "script FAILED" is the extent of the amount of communication your script can have BACK to visual studio.
The script doesn't automatically see all the visual studio environment variables (such as $(InputDir), $(ProjectDir), $(SolutionName), etc), however you can use those variables when you specify how to call the script. In other words, you can pass those values to the script as arguments.
Set this up so that every time you build in Visual Studio, the pre-build event will FIRST try to run make/g++ on your code. If your script (the one that calls make/g++) detects any problems, then the script returns an error and the build can be STOPPED right then and there. The script can print to stdout or stderr and that output should be visible to you in the Visual Studio Build output window (the window that usually shows stuff like "========== Build: 3 succeeded, 0 failed").
You can have the script print:
"BUILD FAILED, non-portable code detected, make/g++ returned the following:........."
This way, you don't have to remember to periodically switch from Visual Studio to the command line. It will be automatically done for you every time you build.
|
62,977 | 70,751 |
How to write a C++ FireFox 3 plugin (not extension) on Windows?
|
Could someone write-up a step by step guide to developing a C++ based plugin for FireFox on Windows?
The links and examples on http://www.mozilla.org/projects/plugins/ are all old and inaccurate - the "NEW" link was added to the page in 2004.
The example could be anything, but I was thinking a plugin that lets JavaScript set the name and then displays "Hello {Name}". To show 2-way communication, it could have a property that returns the full salutation.
Though not as important, it would be nice if the plugin would work in Chrome too.
|
See also http://developer.mozilla.org/en/Plugins . And yes, NPAPI plugins should work in Google Chrome as well.
[edit 2015: Chrome removes support for NPAPI soon http://blog.chromium.org/2014/11/the-final-countdown-for-npapi.html ]
|
63,147 | 63,485 |
User Interface Controls for Win32
|
I see many user interface control libraries for .NET, but where can I get similar stuff for win32 using simply C/C++?
Things like prettier buttons, dials, listviews, graphs, etc.
Seems every Win32 programmers' right of passage is to end up writing his own collection. :/
No MFC controls please. I only do pure C/C++. And with that said, I also don't feel like adding a multi-megabyte framework to my application just so that I can have a prettier button.
I apologize for leaving out one tiny detail, and that is that my development is for Windows Mobile.
So manifest files are out.
I just notice how many developer companies have gone crazy with making pretty looking .NET components and wondered where the equivalent C/C++ Win32 components have gone?
I read about how many people ended up writing their own gradient button class, etc. So you would think that there would be some commercial classes for this stuff. It's just weird.
I'll take a closer look at QT and investigate its GUI support for such things. This is the challenge when you're the one man in your own uISV. No other developers to help you "get things done".
|
I've used Trolltech's Qt framework in the past and had great success with it:
In addition, it's also cross-platform, so in theory you can target Win, Mac, & Linux (provided you don't do anything platform-specific in the rest of your code, of course ;) )
Edit: I notice that you're targeting Windows Mobile; that definitely adds to Qt's strength, as its cross-platform support extends to WinCE and Embedded Linux as well.
|
63,429 | 66,514 |
How do I display dynamic text at the mouse cursor via C++/MFC in a Win32 application
|
I would like to be able to display some dynamic text at the mouse
cursor location in a win32 app, for instance to give an X,Y coordinate that
would move with the cursor as though attached. I can do this during a
mousemove event using a TextOut() call for the window at the mouse
coordinates and invalidate a rectange around a stored last cursor position
to clear up the previous output. However this can suffer from flickering and
cause problems with other things being drawn in a window such as tracker
boxes. Is there a better way to do this, perhaps using the existing cursor
drawing/invalidating mechanism ?
|
You may want to consider a small transparent window that you move to follow the mouse. In particular, since Windows 2000, Layered windows seem to be the weapon of choice (confession: no personal experience there).
|
63,494 | 63,551 |
Does anyone use template metaprogramming in real life?
|
I discovered template metaprogramming more than 5 years ago and got a huge kick out of reading Modern C++ Design but I never found an opertunity to use it in real life.
Have you ever used this technique in real code?
Contributors to Boost need not apply ;o)
|
I once used template metaprogramming in C++ to implement a technique called "symbolic perturbation" for dealing with degenerate input in geometric algorithms. By representing arithmetic expressions as nested templates (i.e. basically by writing out the parse trees by hand) I was able to hand off all the expression analysis to the template processor.
Doing this kind of thing with templates is more efficient than, say, writing expression trees using objects and doing the analysis at runtime. It's faster because the modified (perturbed) expression tree is then available to the optimizer at the same level as the rest of your code, so you get the full benefits of optimization, both within your expressions but also (where possible) between your expressions and the surrounding code.
Of course you could accomplish the same thing by implementing a small DSL (domain specific language) for your expressions and the pasting the translated C++ code into your regular program. That would get you all the same optimization benefits and also be more legible -- but the tradeoff is that you have to maintain a parser.
|
63,784 | 64,682 |
Implementing scripts in c++ app
|
I want to move various parts of my app into simple scripts, to allow people that do not have a strong knowledge of c++ to be able to edit and implement various features.
Because it's a real time app, I need to have some kind of multitasking for these scripts. Ideally I want it so that the c++ app calls a script function which then continues running (under the c++ thread) until either a pause point (Wait(x)), or it returns. In the case of it waiting the state needs to be saved ready for the script to be restarted the next time the app loops after the duration has expired.
The scripts also need to be able to call c++ class methods, ideally using the c++ classes rather than plain wrapper functions around c++ classes.
I don't want to spend a massive amount of time implementing this, so using an existing scripting language is preferred to writing my own. I heard that Python and Lua can be integrated into a c++ app, but I do not know how to do this to achieve my goals.
The scripts must be able to call c++ functions
The scripts must be able to "pause" when certain functions are called (eg. Wait), and be restarted again by the c++ thread
Needs to be fast -- this is for a real time app and there could potentially be a lot of scripts running.
I can probably roll the multitasking code fairly easily, provided the scripts can be saved and restarted (possibly by a different thread to the original).
|
You can use either Lua or Python. Lua is more "lightweight" than python. It's got a smaller memory footprint than python does and in our experience was easier to integrate (people's mileage on this point might vary). It can support a bunch of scripts running simultaneously. Lua, at least, supports stopping/starting threads in the manner you desire.
Boost.python is nice, but in my (limited) experience, it was difficult for us to get compiling for our different environments and was pretty heavyweight. It has (in my opinion) the disadvantage of requiring Boost. For some, that might not be a problem, but if you don't need Boost (or are not using it), you are introducing a ton of code to get Boost.python working. YMMV.
We have built Lua into apps on multiple platforms (win32, Xbox360 and PS3). I believe that it will work on x64. The suggestion to use Luabind is good. We wound up writing our own interface between the two and while not too complicated, having that glue code will save you a lot of time and perhaps aggravation.
With either solution though, debugging can be a pain. We currently have no good solution for debugging Lua scripts that are embedded into our app. Since we haven't used python in our apps I can't speak to what tools might be available there, but a couple of years ago the landscape was roughly the same -- poor debugging. Having scripting to extend functionality is nice, but bugs in the scripts can cause problems and might be difficult to locate.
The Lua code itself is kind of messy to work with if you need to make changes there. We have seen bugs in the Lua codebase itself that were hard to track down. I suspect that Boost::Python might have similar problems.
And with any scripting language, it's not necessarily a solution for "non-programmers" to extend functionality. It might seem like it, but you will likely wind up spending a fair amount of time either debugging scripts or even perhaps Lua.
That all said, we've been very happy with Lua and have shipped it in two games. We currently have no plans to move away from the language. All in all, we've found it better than other alternatives that were available a couple of years ago. Python (and IronPython) are other choices, but based on experience, they seem more heavy handed than Lua. I'd love to hear about other experiences there though.
|
64,498 | 67,478 |
C++ method expansion
|
Can you specialize a template method within a template class without specializing the class template parameter?
Please note that the specialization is on the value of the template parameter, not its type.
This seems to compile under Visual Studio 2008 SP1 complier, but not GCC 4.2.4.
#include <iostream>
using namespace std;
template <typename T>
class A
{
private:
template <bool b>
void testme();
template <>
void testme<true>() { cout << "true" << endl; };
template <>
void testme<false>() { cout << "false" << endl; };
public:
void test();
};
template<typename T> struct select {};
template<> struct select<int> { static const bool value = true; };
template<> struct select<double> { static const bool value = false; };
template <class T>
void A<T>::test() { testme<select<T>::value>(); }
int main(int argc, const char* argv[])
{
A<int> aInt;
A<double> aDouble;
aInt.test();
aDouble.test();
return 0;
}
GCC tells me:"error: explicit specialization in non-namespace scope ‘class A’"
If it is not supported in the standard, can anyone tell me why?
|
Here is another workaround, also useful when you need to partialy specialize a function (which is not allowed). Create a template functor class (ie. class whose sole purpose is to execute a single member function, usually named operator() ), specialize it and then call from within your template function.
I think I learned this trick from Herb Sutter, but do not remember which book (or article) was that. For your needs it is probably overkill, but nonetheless ...
template <typename T>
struct select;
template <bool B>
struct testme_helper
{
void operator()();
};
template <typename T>
class A
{
private:
template <bool B> void testme()
{
testme_helper<B>()();
}
public:
void test()
{
testme<select<T>::value>();
}
};
template<> void testme_helper<true>::operator()()
{
std::cout << "true" << std::endl;
}
template<> void testme_helper<false>::operator()()
{
std::cout << "false" << std::endl;
}
|
64,582 | 64,622 |
C++/Java Performance for Neural Networks?
|
I was discussing neural networks (NN) with a friend over lunch the other day and he claimed the the performance of a NN written in Java would be similar to one written in C++. I know that with 'just in time' compiler techniques Java can do very well, but somehow I just don't buy it. Does anyone have any experience that would shed light on this issue? This page is the extent of my reading on the subject.
|
The Hotspot JIT can now produce code faster than C++. The reason is run-time empirical optimization.
For example, it can see that a certain loop takes the "false" branch 99% of the time and reorder the machine code instructions accordingly.
There's lots of articles about this. If you want all the details, read Sun's excellent whitepaper. For more informal info, try this one.
|
64,645 | 64,974 |
Define an interface in C++ that needs to be implemented in C# and C++
|
I have an interface that I have defined in C++ which now needs to be implemented in C#. What is the best way to go about this? I don't want to use COM at all in my interface definition. The way I have solved this right now is to to have two interface definitions, one in C++ and one in C#. I then expose the C# interfaces as a COM server. This was my application which is written in C++ can call into C#. Is there anyway I can avoid having to define my implementation in C++ as well as C#?
|
If you are willing to use C++/CLI for your managed code instead of C#, then you can just consume the native C++ interface definition directly via the header file. How easy this will be will depend on exactly what is in your interface - simplest case is something that you could use from C.
Take a look at Marcus Heege's Expert C++/CLI: .NET for Visual C++ Programmers, for a lot of helpful information on mixing native and managed C++ in .NET.
|
64,851 | 64,911 |
Macro to test whether an integer type is signed or unsigned
|
How would you write (in C/C++) a macro which tests if an integer type (given as a parameter) is signed or unsigned?
#define is_this_type_signed (my_type) ...
|
If what you want is a simple macro, this should do the trick:
#define is_type_signed(my_type) (((my_type)-1) < 0)
|
64,958 | 65,424 |
What is the best way of preventing memory leaks in a yacc-based parser?
|
Yacc does not permit objects to be passed around. Because the %union can only contain POD types, complex objects must be new'd and passed around by pointer. If a syntax error occurs, the yacc parser just stops running, and references to all of those created objects are lost.
The only solution I've come up with is that all new'd object inherit a particular base class, be added to a container when allocated, and if there is an error everything in that container can be deleted.
Does anyone know of any better yacc tricks to solve this problem?
Please don't tell me to choose a different parser.
|
I love Yacc, but the discriminating union stack does present a challenge.
I don't know whether you are using C or C++. I've modified Yacc to generate C++ for my own purposes, but this solution can be adapted to C.
My preferred solution is to pass an interface to the owner down the parse tree, rather than constructed objects up the stack. Do this by creating your own stack outside of Yacc's. Before you invoke a non-terminal that allocates an object, push the owner of that object to this stack.
For example:
class IExpressionOwner
{
public:
virtual ExpressionAdd *newExpressionAdd() = 0;
virtual ExpressionSubstract *newExpressionSubtract() = 0;
virtual ExpressionMultiply *newExpressionMultiply() = 0;
virtual ExpressionDivide *newExpressionDivide() = 0;
};
class ExpressionAdd : public Expression, public IExpressionOwner
{
private:
std::auto_ptr<Expression> left;
std::auto_ptr<Expression> right;
public:
ExpressionAdd *newExpressionAdd()
{
ExpressionAdd *newExpression = new ExpressionAdd();
std::auto_ptr<Expression> autoPtr(newExpression);
if (left.get() == NULL)
left = autoPtr;
else
right = autoPtr;
return newExpression;
}
...
};
class Parser
{
private:
std::stack<IExpressionOwner *> expressionOwner;
...
};
Everything that wants an expression has to implement the IExpressionOwner interface and push itself to the stack before invoking the expression non-terminal. It's a lot of extra code, but it controls object lifetime.
Update
The expression example is a bad one, since you don't know the operation until after you've reduced the left operand. Still, this technique works in many cases, and requires just a little tweaking for expressions.
|
65,037 | 65,103 |
is there a way to write macros with a variable argument list in visual C++?
|
As far as I know, in gcc you can write something like:
#define DBGPRINT(fmt...) printf(fmt);
Is there a way to do that in VC++?
|
Yes but only since VC++ 2005. The syntax for your example would be:
#define DBGPRINT(fmt, ...) printf(fmt, __VA_ARGS__)
A full reference is here.
|
65,074 | 65,923 |
C++ Unit Testing Legacy Code: How to handle #include?
|
I've just started writing unit tests for a legacy code module with large physical dependencies using the #include directive. I've been dealing with them a few ways that felt overly tedious (providing empty headers to break long #include dependency lists, and using #define to prevent classes from being compiled) and was looking for some better strategies for handling these problems.
I've been frequently running into the problem of duplicating almost every header file with a blank version in order to separate the class I'm testing in it's entirety, and then writing substantial stub/mock/fake code for objects that will need to be replaced since they're now undefined.
Anyone know some better practices?
|
The depression in the responses is overwhelming... But don't fear, we've got the holy book to exorcise the demons of legacy C++ code. Seriously just buy the book if you are in line for more than a week of jousting with legacy C++ code.
Turn to page 127: The case of the horrible include dependencies. (Now I am not even within miles of Michael Feathers but here as-short-as-I-could-manage answer..)
Problem: In C++ if a classA needs to know about ClassB, Class B's declaration is straight-lifted / textually included in the ClassA's source file. And since we programmers love to take it to the wrong extreme, a file can recursively include a zillion others transitively. Builds take years.. but hey atleast it builds.. we can wait.
Now to say 'instantiating ClassA under a test harness is difficult' is an understatement. (Quoting MF's example - Scheduler is our poster problem child with deps galore.)
#include "TestHarness.h"
#include "Scheduler.h"
TEST(create, Scheduler) // your fave C++ test framework macro
{
Scheduler scheduler("fred");
}
This will bring out the includes dragon with a flurry of build errors.
Blow#1 Patience-n-Persistence: Take on each include one at a time and decide if we really need that dependency. Let's assume SchedulerDisplay is one of them, whose displayEntry method is called in Scheduler's ctor.
Blow#2 Fake-it-till-you-make-it (Thanks RonJ):
#include "TestHarness.h"
#include "Scheduler.h"
void SchedulerDisplay::displayEntry(const string& entryDescription) {}
TEST(create, Scheduler)
{
Scheduler scheduler("fred");
}
And pop goes the dependency and all its transitive includes.
You can also reuse the Fake methods by encapsulating it in a Fakes.h file to be included in your test files.
Blow#3 Practice: It may not be always that simple.. but you get the idea. After the first few duels, the process of breaking deps will get easy-n-mechanical
Caveats (Did I mention there are caveats? :)
We need a separate build for test cases in this file ; we can have only 1 definition for the SchedulerDisplay::displayEntry method in a program. So create a separate program for scheduler tests.
We aren't breaking any dependencies in the program, so we are not making the code cleaner.
You need to maintain those fakes as long as we need the tests.
Your sense of aesthetics may be offended for a while.. just bite your lip and 'bear with us for a better tomorrow'
Use this technique for a very huge class with severe dependency issues. Don't use often or lightly.. Use this as a starting point for deeper refactorings. Over time this testing program can be taken behind the barn as you extract more classes (WITH their own tests).
For more.. please do read the book. Invaluable. Fight on bro!
|
65,524 | 65,589 |
Generating a Unique ID in c++
|
What is the best way to generate a Unique ID from two (or more) short ints in C++? I am trying to uniquely identify vertices in a graph. The vertices contain two to four short ints as data, and ideally the ID would be some kind of a hash of them. Prefer portability and uniqueness over speed or ease.
There are a lot of great answers here, I will be trying them all tonight to see what fits my problem the best. A few more words on what I'm doing.
The graph is a collection of samples from an audio file. I use the graph as a Markov Chain to generate a new audio file from the old file. Since each vertex stores a few samples and points to another sample, and the samples are all short ints, it seemed natural to generate an ID from the data. Combining them into a long long sounds good, but maybe something as simple as just a 0 1 2 3 generateID is all I need. not sure how much space is necessary to guarantee uniqueness, if each vertex stores 2 16 bit samples, there are 2^32 possible combinations correct? and so if each vertex stores 4 samples, there are 2^64 possible combinations?
Library and platform specific solutions not really relevant to this question. I don't want anyone else who might compile my program to have to download additional libraries or change the code to suit their OS.
|
A simple solution is to use a 64 bit integer where the lower 16 bits is the first vertex coordinate, next 16 bits is the second, and so on. This will be unique for all your vertices, though not very compact.
So here's some half-assed code to do this. Hopefully I got the casts right.
uint64_t generateId( uint16_t v1, uint16_t v2, uint16_t v3, uint16_t v4)
{
uint64_t id;
id = v1 | (((uint64_t)v2) << 16) | (((uint64_t)v3) << 32) | (((uint64_t)v4) << 48);
return id;
}
Optionally this could be done with a union (great idea from Leon Timmermans, see comment). Very clean this way:
struct vertex
{
uint16_t v1;
uint16_t v2;
uint16_t v3;
uint16_t v4;
};
union vertexWithId
{
vertex v;
uint64_t id;
};
int main()
{
vertexWithId vWithId;
// Setup your vertices
vWithId.v.v1 = 2;
vWithId.v.v2 = 5;
// Your id is automatically setup for you!
std::cout << "Id is " << vWithId.id << std::endl;
return 0;
}
|
65,724 | 66,036 |
Uninitialized memory blocks in VC++
|
As everyone knows, the Visual C++ runtime marks uninitialized or just freed memory blocks with special non-zero markers. Is there any way to disable this behavior entirely without manually setting all uninitialized memory to zeros? It's causing havoc with my valid not null checks, since 0xFEEEFEEE != 0.
Hrm, perhaps I should explain a bit better. I create and initialize a variable (via new), and that all goes just fine. When I free it (via delete), it sets the pointer to 0xFEEEFEEE instead of NULL. When I insert a proper check for NULL, as all good programs that manage their own memory should, I come up with problems as 0xFEEEFEEE passes a NULL check without problems. Is there any good way, other than manually setting all pointers to NULL when deleting them, to detect when memory has already been freed? I would prefer to not use Boost simply because I don't want the overhead, small though it may be, since that's the only thing I'd be using Boost for.
|
It is not the responsibility of delete to reset all the pointers to the object to NULL.
Also you shouldn't change the default memory fill for the windows DEBUG runtime and you should use some thing like boost::shared_ptr<> for pointers any way.
That said, if you really want to shoot your self in the foot you can.
You can change the default fill for the windows DEBUG runtime by using an allocator hook like this. This will only work on HEAP allocated object!
int main(int argc,char** arv)
{
// Call first to register hook
_CrtSetAllocHook(&zero_fill);
// Do other stuff
malloc(100);
}
int zero_fill(int nAllocType,
void* pvData,
size_t nSize,
int nBlockUse,
long lRequest,
const unsigned char *szFileName,
int nLine )
{
/// Very Importaint !!
/// infinite recursion if this is removed !!
/// _CRT_BLOCK must not do any thing but return TRUE
/// even calling printf in the _CRT_BLOCK will cause
/// infinite recursion
if ( nBlockUse == _CRT_BLOCK )
return( TRUE );
switch(nAllocType)
{
case _HOOK_ALLOC:
case _HOOK_REALLOC:
// zero initialize the allocated space.
memset(pvData,0,nSize);
break;
case _HOOK_FREE:
break;
}
return TRUE;
}
|
66,166 | 66,239 |
C++ web service framework
|
We are looking for a C++ Soap web services framework that support RPC, preferably open source.
Any recommendations?
|
WSO2 Web Services Framework for C++ (WSO2 WSF/C++), a binding of WSO2 WSF/C into C++ is a C++ extension for consuming Web Services in C++.
http://wso2.org/projects/wsf/cpp
Apache Axis is an open source, XML based Web service framework. It consists of a Java and a C++ implementation of the SOAP server, and various utilities and APIs for generating and deploying Web service applications.
http://ws.apache.org/axis/
|
67,174 | 78,553 |
Find memory leaks caused by smart pointers
|
Does anybody know a "technique" to discover memory leaks caused by smart pointers? I am currently working on a large project written in C++ that heavily uses smart pointers with reference counting. Obviously we have some memory leaks caused by smart pointers, that are still referenced somewhere in the code, so that their memory does not get free'd. It's very hard to find the line of code with the "needless" reference, that causes the corresponding object not to be free'd (although it's not of use any longer).
I found some advice in the web, that proposed to collect call stacks of the increment/decrement operations of the reference counter. This gives me a good hint, which piece of code has caused the reference counter to get increased or decreased.
But what I need is some kind of algorithm that groups the corresponding "increase/decrease call stacks" together. After removing these pairs of call stacks, I hopefully have (at least) one "increase call stack" left over, that shows me the piece of code with the "needless" reference, that caused the corresponding object not to be freed. Now it will be no big deal to fix the leak!
But has anybody an idea for an "algorithm" that does the grouping?
Development takes place under Windows XP.
(I hope someone understood, what I tried to explain ...)
EDIt: I am talking about leaks caused by circular references.
|
Note that one source of leaks with reference-counting smart pointers are pointers with circular dependancies. For example, A have a smart pointer to B, and B have a smart pointer to A. Neither A nor B will be destroyed. You will have to find, and then break the dependancies.
If possible, use boost smart pointers, and use shared_ptr for pointers which are supposed to be owners of the data, and weak_ptr for pointers not supposed to call delete.
|
67,273 | 67,307 |
How do you iterate through every file/directory recursively in standard C++?
|
How do you iterate through every file/directory recursively in standard C++?
|
In standard C++, technically there is no way to do this since standard C++ has no conception of directories. If you want to expand your net a little bit, you might like to look at using Boost.FileSystem. This has been accepted for inclusion in TR2, so this gives you the best chance of keeping your implementation as close as possible to the standard.
An example, taken straight from the website:
bool find_file( const path & dir_path, // in this directory,
const std::string & file_name, // search for this name,
path & path_found ) // placing path here if found
{
if ( !exists( dir_path ) ) return false;
directory_iterator end_itr; // default construction yields past-the-end
for ( directory_iterator itr( dir_path );
itr != end_itr;
++itr )
{
if ( is_directory(itr->status()) )
{
if ( find_file( itr->path(), file_name, path_found ) ) return true;
}
else if ( itr->leaf() == file_name ) // see below
{
path_found = itr->path();
return true;
}
}
return false;
}
|
67,426 | 67,701 |
Dynamically sorted STL containers
|
I'm fairly new to the STL, so I was wondering whether there are any dynamically sortable containers? At the moment my current thinking is to use a vector in conjunction with the various sort algorithms, but I'm not sure whether there's a more appropriate selection given the (presumably) linear complexity of inserting entries into a sorted vector.
To clarify "dynamically", I am looking for a container that I can modify the sorting order at runtime - e.g. sort it in an ascending order, then later re-sort in a descending order.
|
If you know you're going to be sorting on a single value ascending and descending, then set is your friend. Use a reverse iterator when you want to "sort" in the opposite direction.
If your objects are complex and you're going to be sorting in many different ways based on the member fields within the objects, then you're probably better off with using a vector and sort. Try to do your inserts all at once, and then call sort once. If that isn't feasible, then deque may be a better option than the vector for large collections of objects.
I think that if you're interested in that level of optimization, you had better be profiling your code using actual data. (Which is probably the best advice anyone here can give: it may not matter that you call sort after each insert if you're only doing it once in a blue moon.)
|
67,554 | 67,577 |
What's the best free C++ profiler for Windows?
|
I'm looking for a profiler in order to find the bottleneck in my C++ code. I'd like to find a free, non-intrusive, and good profiling tool. I'm a game developer, and I use PIX for Xbox 360 and found it very good, but it's not free. I know the Intel VTune, but it's not free either.
|
CodeXL has now superseded the End Of Line'd AMD Code Analyst and both are free, but not as advanced as VTune.
There's also Sleepy, which is very simple, but does the job in many cases.
Note: All three of the tools above are unmaintained since several years.
|
67,894 | 67,930 |
Why do we need extern "C"{ #include <foo.h> } in C++?
|
Why do we need to use:
extern "C" {
#include <foo.h>
}
Specifically:
When should we use it?
What is happening at the compiler/linker level that requires us to use it?
How in terms of compilation/linking does this solve the problems which require us to use it?
|
C and C++ are superficially similar, but each compiles into a very different set of code. When you include a header file with a C++ compiler, the compiler is expecting C++ code. If, however, it is a C header, then the compiler expects the data contained in the header file to be compiled to a certain format—the C++ 'ABI', or 'Application Binary Interface', so the linker chokes up. This is preferable to passing C++ data to a function expecting C data.
(To get into the really nitty-gritty, C++'s ABI generally 'mangles' the names of their functions/methods, so calling printf() without flagging the prototype as a C function, the C++ will actually generate code calling _Zprintf, plus extra crap at the end.)
So: use extern "C" {...} when including a c header—it's that simple. Otherwise, you'll have a mismatch in compiled code, and the linker will choke. For most headers, however, you won't even need the extern because most system C headers will already account for the fact that they might be included by C++ code and already extern "C" their code.
|
68,084 | 68,130 |
Switching from C# to C++. Any must-reads?
|
I'm trying to find a least-resistance path from C# to C++, and while I feel I handle C# pretty well after two solid years, I'm still not sure I've gotten the "groove" of C++, despite numerous attempts.
Are there any particular books or websites that might be suitable for this transition?
|
I recommend The C++ Programming language by Bjarne Stroustrup. It's not a suitable book for new programmers, but I found it quite effective as programmer who was experienced in other languages and didn't want to waste too much time with learning how while loops work. It's a dense but quite comprehensive book.
|
68,144 | 999,308 |
Using XmlRpc in C++ and Windows
|
I need to use XmlRpc in C++ on a Windows platform. Despite the fact that my friends assure me that XmlRpc is a "widely available standard technology", there are not many libraries available for it. In fact I only found one library to do this on Windows, (plus another one that claims "you'll have to do a lot of work to get this to compile on Windows). The library I found was Chris Morley's "XmlRpc++". However, it doesn't have support for SSL.
My question therefore is: what library should I be using?
|
I've written my own C++ library. It's available at sourceforge:
xmlrpcc4win
The reason I wrote it rather than using Chris Morley's was that:
The Windows "wininet.lib" library gives you all the functionality for handling Http requests, so I'd rather use that. As a result, I only needed 1700 LOC.
"wininet.lib", and therefore my implementation, supports HTTPS
Chris Morley's use of STL containers was quite inefficient (Chris, mail me if you read this).
|
69,112 | 69,169 |
What is a symbol table?
|
Can someone describe what a symbol table is within the context of C and C++?
|
There are two common and related meaning of symbol tables here.
First, there's the symbol table in your object files. Usually, a C or C++ compiler compiles a single source file into an object file with a .obj or .o extension. This contains a collection of executable code and data that the linker can process into a working application or shared library. The object file has a data structure called a symbol table in it that maps the different items in the object file to names that the linker can understand. If you call a function from your code, the compiler doesn't put the final address of the routine in the object file. Instead, it puts a placeholder value into the code and adds a note that tells the linker to look up the reference in the various symbol tables from all the object files it's processing and stick the final location there.
Second, there's also the symbol table in a shared library or DLL. This is produced by the linker and serves to name all the functions and data items that are visible to users of the library. This allows the system to do run-time linking, resolving open references to those names to the location where the library is loaded in memory.
If you want to learn more, I suggest John Levine's excellent book "Linkers and Loaders".link text
|
69,115 | 69,218 |
char[] to hex string exercise
|
Below is my current char* to hex string function. I wrote it as an exercise in bit manipulation. It takes ~7ms on a AMD Athlon MP 2800+ to hexify a 10 million byte array. Is there any trick or other way that I am missing?
How can I make this faster?
Compiled with -O3 in g++
static const char _hex2asciiU_value[256][2] =
{ {'0','0'}, {'0','1'}, /* snip..., */ {'F','E'},{'F','F'} };
std::string char_to_hex( const unsigned char* _pArray, unsigned int _len )
{
std::string str;
str.resize(_len*2);
char* pszHex = &str[0];
const unsigned char* pEnd = _pArray + _len;
clock_t stick, etick;
stick = clock();
for( const unsigned char* pChar = _pArray; pChar != pEnd; pChar++, pszHex += 2 ) {
pszHex[0] = _hex2asciiU_value[*pChar][0];
pszHex[1] = _hex2asciiU_value[*pChar][1];
}
etick = clock();
std::cout << "ticks to hexify " << etick - stick << std::endl;
return str;
}
Updates
Added timing code
Brian R. Bondy: replace the std::string with a heap alloc'd buffer and change ofs*16 to ofs << 4 - however the heap allocated buffer seems to slow it down? - result ~11ms
Antti Sykäri:replace inner loop with
int upper = *pChar >> 4;
int lower = *pChar & 0x0f;
pszHex[0] = pHex[upper];
pszHex[1] = pHex[lower];
result ~8ms
Robert: replace _hex2asciiU_value with a full 256-entry table, sacrificing memory space but result ~7ms!
HoyHoy: Noted it was producing incorrect results
|
At the cost of more memory you can create a full 256-entry table of the hex codes:
static const char _hex2asciiU_value[256][2] =
{ {'0','0'}, {'0','1'}, /* ..., */ {'F','E'},{'F','F'} };
Then direct index into the table, no bit fiddling required.
const char *pHexVal = pHex[*pChar];
pszHex[0] = pHexVal[0];
pszHex[1] = pHexVal[1];
|
69,250 | 69,252 |
Why does a C/C++ program often have optimization turned off in debug mode?
|
In most C or C++ environments, there is a "debug" mode and a "release" mode compilation.
Looking at the difference between the two, you find that the debug mode adds the debug symbols (often the -g option on lots of compilers) but it also disables most optimizations.
In "release" mode, you usually have all sorts of optimizations turned on.
Why the difference?
|
Without any optimization on, the flow through your code is linear. If you are on line 5 and single step, you step to line 6. With optimization on, you can get instruction re-ordering, loop unrolling and all sorts of optimizations.
For example:
void foo() {
1: int i;
2: for(i = 0; i < 2; )
3: i++;
4: return;
In this example, without optimization, you could single step through the code and hit lines 1, 2, 3, 2, 3, 2, 4
With optimization on, you might get an execution path that looks like: 2, 3, 3, 4 or even just 4! (The function does nothing after all...)
Bottom line, debugging code with optimization enabled can be a royal pain! Especially if you have large functions.
Note that turning on optimization changes the code! In certain environment (safety critical systems), this is unacceptable and the code being debugged has to be the code shipped. Gotta debug with optimization on in that case.
While the optimized and non-optimized code should be "functionally" equivalent, under certain circumstances, the behavior will change.
Here is a simplistic example:
int* ptr = 0xdeadbeef; // some address to memory-mapped I/O device
*ptr = 0; // setup hardware device
while(*ptr == 1) { // loop until hardware device is done
// do something
}
With optimization off, this is straightforward, and you kinda know what to expect.
However, if you turn optimization on, a couple of things might happen:
The compiler might optimize the while block away (we init to 0, it'll never be 1)
Instead of accessing memory, pointer access might be moved to a register->No I/O Update
memory access might be cached (not necessarily compiler optimization related)
In all these cases, the behavior would be drastically different and most likely wrong.
|
69,539 | 12,116,668 |
Have you used any of the C++ interpreters (not compilers)?
|
I am curious if anyone have used UnderC, Cint, Cling, Ch, or any other C++ interpreter and could share their experience.
|
There is cling Cern's project of C++ interpreter based on clang - it's new approach based on 20 years of experience in ROOT cint and it's quite stable and recommended by Cern guys.
Here is nice Google Talk: Introducing cling, a C++ Interpreter Based on clang/LLVM.
|
69,738 | 69,765 |
C++: how to get fprintf results as a std::string w/o sprintf
|
I am working with an open-source UNIX tool that is implemented in C++, and I need to change some code to get it to do what I want. I would like to make the smallest possible change in hopes of getting my patch accepted upstream. Solutions that are implementable in standard C++ and do not create more external dependencies are preferred.
Here is my problem. I have a C++ class -- let's call it "A" -- that currently uses fprintf() to print its heavily formatted data structures to a file pointer. In its print function, it also recursively calls the identically defined print functions of several member classes ("B" is an example). There is another class C that has a member std::string "foo" that needs to be set to the print() results of an instance of A. Think of it as a to_str() member function for A.
In pseudocode:
class A {
public:
...
void print(FILE* f);
B b;
...
};
...
void A::print(FILE *f)
{
std::string s = "stuff";
fprintf(f, "some %s", s);
b.print(f);
}
class C {
...
std::string foo;
bool set_foo(std::str);
...
}
...
A a = new A();
C c = new C();
...
// wish i knew how to write A's to_str()
c.set_foo(a.to_str());
I should mention that C is fairly stable, but A and B (and the rest of A's dependents) are in a state of flux, so the less code changes necessary the better. The current print(FILE* F) interface also needs to be preserved. I have considered several approaches to implementing A::to_str(), each with advantages and disadvantages:
Change the calls to fprintf() to sprintf()
I wouldn't have to rewrite any format strings
print() could be reimplemented as: fprint(f, this.to_str());
But I would need to manually allocate char[]s, merge a lot of c strings , and finally convert the character array to a std::string
Try to catch the results of a.print() in a string stream
I would have to convert all of the format strings to << output format. There are hundreds of fprintf()s to convert :-{
print() would have to be rewritten because there is no standard way that I know of to create an output stream from a UNIX file handle (though this guy says it may be possible).
Use Boost's string format library
More external dependencies. Yuck.
Format's syntax is different enough from printf() to be annoying:
printf(format_str, args) -> cout << boost::format(format_str) % arg1 % arg2 % etc
Use Qt's QString::asprintf()
A different external dependency.
So, have I exhausted all possible options? If so, which do you think is my best bet? If not, what have I overlooked?
Thanks.
|
I am using #3: the boost string format library - but I have to admit that I've never had any problem with the differences in format specifications.
Works like a charm for me - and the external dependencies could be worse (a very stable library)
Edited: adding an example how to use boost::format instead of printf:
sprintf(buffer, "This is a string with some %s and %d numbers", "strings", 42);
would be something like this with the boost::format library:
string = boost::str(boost::format("This is a string with some %s and %d numbers") %"strings" %42);
Hope this helps clarify the usage of boost::format
I've used boost::format as a sprintf / printf replacement in 4 or 5 applications (writing formatted strings to files, or custom output to logfiles) and never had problems with format differences. There may be some (more or less obscure) format specifiers which are differently - but I never had a problem.
In contrast I had some format specifications I couldn't really do with streams (as much as I remember)
|
70,013 | 70,630 |
How to Detect if I'm Compiling Code with a particular Visual Studio version?
|
Is there any way to know if I'm compiling under a specific Microsoft Visual Studio version?
|
_MSC_VER and possibly _MSC_FULL_VER is what you need. You can also examine visualc.hpp in any recent boost install for some usage examples.
Some values for the more recent versions of the compiler are:
MSVC++ 14.24 _MSC_VER == 1924 (Visual Studio 2019 version 16.4)
MSVC++ 14.23 _MSC_VER == 1923 (Visual Studio 2019 version 16.3)
MSVC++ 14.22 _MSC_VER == 1922 (Visual Studio 2019 version 16.2)
MSVC++ 14.21 _MSC_VER == 1921 (Visual Studio 2019 version 16.1)
MSVC++ 14.2 _MSC_VER == 1920 (Visual Studio 2019 version 16.0)
MSVC++ 14.16 _MSC_VER == 1916 (Visual Studio 2017 version 15.9)
MSVC++ 14.15 _MSC_VER == 1915 (Visual Studio 2017 version 15.8)
MSVC++ 14.14 _MSC_VER == 1914 (Visual Studio 2017 version 15.7)
MSVC++ 14.13 _MSC_VER == 1913 (Visual Studio 2017 version 15.6)
MSVC++ 14.12 _MSC_VER == 1912 (Visual Studio 2017 version 15.5)
MSVC++ 14.11 _MSC_VER == 1911 (Visual Studio 2017 version 15.3)
MSVC++ 14.1 _MSC_VER == 1910 (Visual Studio 2017 version 15.0)
MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015 version 14.0)
MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013 version 12.0)
MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012 version 11.0)
MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010 version 10.0)
MSVC++ 9.0 _MSC_FULL_VER == 150030729 (Visual Studio 2008, SP1)
MSVC++ 9.0 _MSC_VER == 1500 (Visual Studio 2008 version 9.0)
MSVC++ 8.0 _MSC_VER == 1400 (Visual Studio 2005 version 8.0)
MSVC++ 7.1 _MSC_VER == 1310 (Visual Studio .NET 2003 version 7.1)
MSVC++ 7.0 _MSC_VER == 1300 (Visual Studio .NET 2002 version 7.0)
MSVC++ 6.0 _MSC_VER == 1200 (Visual Studio 6.0 version 6.0)
MSVC++ 5.0 _MSC_VER == 1100 (Visual Studio 97 version 5.0)
The version number above of course refers to the major version of your Visual studio you see in the about box, not to the year in the name. A thorough list can be found here. Starting recently, Visual Studio will start updating its ranges monotonically, meaning you should check ranges, rather than exact compiler values.
cl.exe /? will give a hint of the used version, e.g.:
c:\program files (x86)\microsoft visual studio 11.0\vc\bin>cl /?
Microsoft (R) C/C++ Optimizing Compiler Version 17.00.50727.1 for x86
.....
|
70,643 | 72,091 |
Setting Excel Number Format via xlcFormatNumber in an xll
|
I'm trying to set the number format of a cell but the call to xlcFormatNumber fails leaving the cell number format as "General". I can successfully set the value of the cell using xlSet.
XLOPER xRet;
XLOPER xRef;
//try to set the format of cell A1
xRef.xltype = xltypeSRef;
xRef.val.sref.count = 1;
xRef.val.sref.ref.rwFirst = 0;
xRef.val.sref.ref.rwLast = 0;
xRef.val.sref.ref.colFirst = 0;
xRef.val.sref.ref.colLast = 0;
XLOPER xFormat;
xFormat.xltype = xltypeStr;
xFormat.val.str = "\4#.00"; //I've tried various formats
Excel4( xlcFormatNumber, &xRet, 2, (LPXLOPER)&xRef, (LPXLOPER)&xFormat);
I haven't managed to find any documentation regarding the usage of this command. Any help here would be greatly appreciated.
|
Thanks to Simon Murphy for the answer:-
Smurf on Spreadsheets
//It is necessary to select the cell to apply the formatting to
Excel4 (xlcSelect, 0, 1, &xRef);
//Then we apply the formatting
Excel4( xlcFormatNumber, 0, 1, &xFormat);
|
70,880 | 70,905 |
deleting a buffer through a different type of pointer?
|
Say I have the following C++:
char *p = new char[cb];
SOME_STRUCT *pSS = (SOME_STRUCT *) p;
delete pSS;
Is this safe according to the C++ standard? Do I need to cast back to a char* and then use delete[]? I know it'll work in most C++ compilers, because it's plain-ordinary-data, with no destructors. Is it guaranteed to be safe?
|
It's not guaranteed to be safe. Here's a relevant link in the C++ FAQ lite:
[16.13] Can I drop the [] when deleting array of some built-in type (char, int, etc.)?
http://www.parashift.com/c++-faq-lite/freestore-mgmt.html#faq-16.13
|
71,108 | 71,298 |
To what use is multiple indirection in C++?
|
Under what circumstances might you want to use multiple indirection (that is, a chain of pointers as in Foo **) in C++?
|
Most common usage as @aku pointed out is to allow a change to a pointer parameter to be visible after the function returns.
#include <iostream>
using namespace std;
struct Foo {
int a;
};
void CreateFoo(Foo** p) {
*p = new Foo();
(*p)->a = 12;
}
int main(int argc, char* argv[])
{
Foo* p = NULL;
CreateFoo(&p);
cout << p->a << endl;
delete p;
return 0;
}
This will print
12
But there are several other useful usages as in the following example to iterate an array of strings and print them to the standard output.
#include <iostream>
using namespace std;
int main(int argc, char* argv[])
{
const char* words[] = { "first", "second", NULL };
for (const char** p = words; *p != NULL; ++p) {
cout << *p << endl;
}
return 0;
}
|
71,416 | 72,599 |
Forward declaring an enum in C++
|
I'm trying to do something like the following:
enum E;
void Foo(E e);
enum E {A, B, C};
which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain?
Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as
enum E {
FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X
}
as project X is not something I want my users to know about.
So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people.
As for the compiler - it's GCC.
|
The reason the enum can't be forward declared is that, without knowing the values, the compiler can't know the storage required for the enum variable. C++ compilers are allowed to specify the actual storage space based on the size necessary to contain all the values specified. If all that is visible is the forward declaration, the translation unit can't know what storage size has been chosen – it could be a char, or an int, or something else.
From Section 7.2.5 of the ISO C++ Standard:
The underlying type of an enumeration is an integral type that can represent all the enumerator values defined in the enumeration. It is implementation-defined which integral type is used as the underlying type for an enumeration except that the underlying type shall not be larger than int unless the value of an enumerator cannot fit in an int or unsigned int. If the enumerator-list is empty, the underlying type is as if the enumeration had a single enumerator with value 0. The value of sizeof() applied to an enumeration type, an object of enumeration type, or an enumerator, is the value of sizeof() applied to the underlying type.
Since the caller to the function must know the sizes of the parameters to correctly set up the call stack, the number of enumerations in an enumeration list must be known before the function prototype.
Update:
In C++0X, a syntax for forward declaring enum types has been proposed and accepted. You can see the proposal at Forward declaration of enumerations (rev.3)
|
71,475 | 1,198,602 |
Virtual Files are opened from Temporary Internet Files
|
I have created a namespace extension that is rooted under Desktop. The main purpose of the extension is to provide a virtual list of ZIP files that represent a list of configurable directories. When the user clicks one of the those items the contents of the related directory are zipped in place and the resulting ZIP file is stored in a cache folder.
All this works well aside a minor issue. If we go to Windows Explorer, open the extension and double click an item the opened file is the one from the cache. [CORRECT]
If on the other hand we open it by an Open Dialog the opened file is one from a Temporary Internet files directory. [INCORRECT]
What do I have to change for the Open Dialog (when used for example trough notepad.exe) to open the file from the cache folder and not from Temporary Internet files. I have tried to send allways the qualified file name in IShellFolder::GetDisplayNameOf but without any luck.
|
The problem was fixed by masking SFGAO_FILESYSTEM in the attributes returned by implementation of interface method IShellFolder::GetAttributesOf.
|
72,010 | 72,075 |
C++ overload resolution
|
Given the following example, why do I have to explicitly use the statement b->A::DoSomething() rather than just b->DoSomething()?
Shouldn't the compiler's overload resolution figure out which method I'm talking about?
I'm using Microsoft VS 2005. (Note: using virtual doesn't help in this case.)
class A
{
public:
int DoSomething() {return 0;};
};
class B : public A
{
public:
int DoSomething(int x) {return 1;};
};
int main()
{
B* b = new B();
b->A::DoSomething(); //Why this?
//b->DoSomething(); //Why not this? (Gives compiler error.)
delete b;
return 0;
}
|
The two “overloads” aren't in the same scope. By default, the compiler only considers the smallest possible name scope until it finds a name match. Argument matching is done afterwards. In your case this means that the compiler sees B::DoSomething. It then tries to match the argument list, which fails.
One solution would be to pull down the overload from A into B's scope:
class B : public A {
public:
using A::DoSomething;
// …
}
|
72,128 | 72,238 |
Fastest way to find if a 3D coordinate is already used
|
Using C++ (and Qt), I need to process a big amount of 3D coordinates.
Specifically, when I receive a 3D coordinate (made of 3 doubles), I need to check in a list if this coordinate has already been processed.
If not, then I process it and add it to the list (or container).
The amount of coordinates can become very big, so I need to store the processed coordinates in a container which will ensure that checking if a 3D coordinate is already contained in the container is fast.
I was thinking of using a map of a map of a map, storing the x coordinate, then the y coordinate then the z coordinate, but this makes it quite tedious to use, so I'm actually hoping there is a much better way to do it that I cannot think of.
|
Probably the simplest way to speed up such processing is to store the already-processed points in Octree. Checking for duplication will become close to logarithmic.
Also, make sure you tolerate round-off errors by checking the distance between the points, not the equality of the coordinates.
|
72,271 | 72,409 |
"No newline at end of file" compiler warning
|
What is the reason for the following warning in some C++ compilers?
No newline at end of file
Why should I have an empty line at the end of a source/header file?
|
Think of some of the problems that can occur if there is no newline. According to the ANSI standard the #include of a file at the beginning inserts the file exactly as it is to the front of the file and does not insert the new line after the #include <foo.h> after the contents of the file. So if you include a file with no newline at the end to the parser it will be viewed as if the last line of foo.h is on the same line as the first line of foo.cpp. What if the last line of foo.h was a comment without a new line? Now the first line of foo.cpp is commented out. These are just a couple of examples of the types of problems that can creep up.
Just wanted to point any interested parties to James' answer below. While the above answer is still correct for C, the new C++ standard (C++11) has been changed so that this warning should no longer be issued if using C++ and a compiler conforming to C++11.
From C++11 standard via James' post:
A source file that is not empty and that does not end in a new-line character, or that ends in a new-line character immediately preceded by a backslash character before any such splicing takes place, shall be processed as if an additional new-line character were appended to the file (C++11 §2.2/1).
|
72,552 | 72,617 |
Why does volatile exist?
|
What does the volatile keyword do? In C++ what problem does it solve?
In my case, I have never knowingly needed it.
|
volatile is needed if you are reading from a spot in memory that, say, a completely separate process/device/whatever may write to.
I used to work with dual-port ram in a multiprocessor system in straight C. We used a hardware managed 16 bit value as a semaphore to know when the other guy was done. Essentially we did this:
void waitForSemaphore()
{
volatile uint16_t* semPtr = WELL_KNOWN_SEM_ADDR;/*well known address to my semaphore*/
while ((*semPtr) != IS_OK_FOR_ME_TO_PROCEED);
}
Without volatile, the optimizer sees the loop as useless (The guy never sets the value! He's nuts, get rid of that code!) and my code would proceed without having acquired the semaphore, causing problems later on.
|
72,616 | 72,786 |
Embed data in a C++ program
|
I've got a C++ program that uses SQLite. I want to store the SQL queries in a separate file -- a plain-text file, not a source code file -- but embed that file in the executable file like a resource.
(This has to run on Linux, so I can't store it as an actual resource as far as I know, though that would be perfect if it were for Windows.)
Is there any simple way to do it, or will it effectively require me to write my own resource system for Linux? (Easily possible, but it would take a lot longer.)
|
You can use objcopy to bind the contents of the file to a symbol your program can use. See, for instance, here for more information.
|
72,769 | 73,075 |
Static libraries with managed code issue
|
Problem (simplified to make things clearer):
1. there is one statically-linked static.lib that has a function that increments:
extern int CallCount = 0;
int TheFunction()
{
void *p = &CallCount;
printf("Function called");
return CallCount++;
}
2. static.lib is linked into a managed C++/CLI managed.dll that wraps TheFunction method:
int Managed::CallLibFunc()
{
return TheFunction();
}
3. Test app has a reference to managed.dll and creates multiple domains that call C++/CLI wrapper:
static void Main(string[] args)
{
Managed c1 = new Managed();
int val1 = c1.CallLibFunc();
// value is zero
AppDomain ad = AppDomain.CreateDomain("NewDomain");
Managed c = ad.CreateInstanceAndUnwrap(a.FullName, typeof(Managed).FullName) as Managed;
int val2 = c.CallLibFunc();
// value is one
}
Question:
Based on what I have read in Essential .NET Vol1 The CLR by Don Box, I would expect val2 to be zero since a brand new copy of managed.dll/static.lib is loaded when CreateInstanceAndUnwrap is called. Am I misunderstanding what is happening? The static library does not seem to be respecting the appdomain boundaries since it's unmanaged code. Is there a way to get around this issue other than by creating a brand new process for instantiating Managed?
Thank you very much everyone!
|
My hunch was that, as you suspected, unmanaged DLLs are loaded in the context of the process and not in the context of the AppDomain, so any static data in unmanaged code is shared among AppDomains.
This link shows someone with the same problem you have, still not 100% verification of this, but probably this is the case.
This link is about creating a callback from unmanaged code into an AppDomain using a thunking trick. I'm not sure this can help you but maybe you'll find this useful to create some kind of a workaround.
|
72,789 | 72,877 |
Change app icon in Visual Studio 2005?
|
I'd like to use a different icon for the demo version of my game, and I'm building the demo with a different build config than I do for the full verison, using a preprocessor define to lockout some content, use different graphics, etc. Is there a way that I can make Visual Studio use a different icon for the app Icon in the demo config but continue to use the regular icon for the full version's config?
|
According to this page you may use preprocessor directives in your *.rc file. You should write something like this
#ifdef _DEMO_VERSION_
IDR_MAINFRAME ICON "demo.ico"
#else
IDR_MAINFRAME ICON "full.ico"
#endif
|
73,117 | 73,537 |
Making a game in C++ using parallel processing
|
I wanted to "emulate" a popular flash game, Chrontron, in C++ and needed some help getting started. (NOTE: Not for release, just practicing for myself)
Basics:
Player has a time machine. On each iteration of using the time machine, a parallel state
is created, co-existing with a previous state. One of the states must complete all the
objectives of the level before ending the stage. In addition, all the stages must be able
to end the stage normally, without causing a state paradox (wherein they should have
been able to finish the stage normally but, due to the interactions of another state,
were not).
So, that sort of explains how the game works. You should play it a bit to really
understand what my problem is.
I'm thinking a good way to solve this would be to use linked lists to store each state,
which will probably either be a hash map, based on time, or a linked list that iterates
based on time. I'm still unsure.
ACTUAL QUESTION:
Now that I have some rough specs, I need some help deciding on which data structures to use for this, and why. Also, I want to know what Graphics API/Layer I should use to do this: SDL, OpenGL, or DirectX (my current choice is SDL). And how would I go about implementing parallel states? With parallel threads?
EDIT (To clarify more):
OS -- Windows (since this is a hobby project, may do this in Linux later)
Graphics -- 2D
Language -- C++ (must be C++ -- this is practice for a course next semester)
Q-Unanswered: SDL : OpenGL : Direct X
Q-Answered: Avoid Parallel Processing
Q-Answered: Use STL to implement time-step actions.
So far from what people have said, I should:
1. Use STL to store actions.
2. Iterate through actions based on time-step.
3. Forget parallel processing -- period. (But I'd still like some pointers as to how it
could be used and in what cases it should be used, since this is for practice).
Appending to the question, I've mostly used C#, PHP, and Java before so I wouldn't describe myself as a hotshot programmer. What C++ specific knowledge would help make this project easier for me? (ie. Vectors?)
|
What you should do is first to read and understand the "fixed time-step" game loop (Here's a good explanation: http://www.gaffer.org/game-physics/fix-your-timestep).
Then what you do is to keep a list of list of pairs of frame counter and action. STL example:
std::list<std::list<std::pair<unsigned long, Action> > > state;
Or maybe a vector of lists of pairs. To create the state, for every action (player interaction) you store the frame number and what action is performed, most likely you'd get the best results if action simply was "key <X> pressed" or "key <X> released":
state.back().push_back(std::make_pair(currentFrame, VK_LEFT | KEY_PRESSED));
To play back the previous states, you'd have to reset the frame counter every time the player activates the time machine and then iterate through the state list for each previous state and see if any matches the current frame. If there is, perform the action for that state.
To optimize you could keep a list of iterators to where you are in each previous state-list. Here's some pseudo-code for that:
typedef std::list<std::pair<unsigned long, Action> > StateList;
std::list<StateList::iterator> stateIteratorList;
//
foreach(it in stateIteratorList)
{
if(it->first == currentFrame)
{
performAction(it->second);
++it;
}
}
I hope you get the idea...
Separate threads would simply complicate the matter greatly, this way you get the same result every time, which you cannot guarantee by using separate threads (can't really see how that would be implemented) or a non-fixed time-step game loop.
When it comes to graphics API, I'd go with SDL as it's probably the easiest thing to get you started. You can always use OpenGL from SDL later on if you want to go 3D.
|
73,134 | 73,163 |
Will this C++ code cause a memory leak (casting array new)
|
I have been working on some legacy C++ code that uses variable length structures (TAPI), where the structure size will depend on variable length strings. The structures are allocated by casting array new thus:
STRUCT* pStruct = (STRUCT*)new BYTE[sizeof(STRUCT) + nPaddingSize];
Later on however the memory is freed using a delete call:
delete pStruct;
Will this mix of array new[] and non-array delete cause a memory leak or would it depend on the compiler? Would I be better off changing this code to use malloc and free instead?
|
Technically I believe it could cause a problem with mismatched allocators, though in practice I don't know of any compiler that would not do the right thing with this example.
More importantly if STRUCT where to have (or ever be given) a destructor then it would invoke the destructor without having invoked the corresponding constructor.
Of course, if you know where pStruct came from why not just cast it on delete to match the allocation:
delete [] (BYTE*) pStruct;
|
73,686 | 73,711 |
cout prints "-0" instead of "0"
|
#include <iostream>
using namespace std;
int main()
{
double u = 0;
double w = -u;
cout << w << endl;
return 0;
}
Why does this great piece of code output -0 and not 0, as one would expect?
|
The IEEE 754 standard for floating-point numbers has the sign bit separate from the mantissa, which allows for zero to be negative. Wikipedia should be able to help explain this.
|
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