# gcov

## NAME



           gcov - coverage testing tool
    


## SYNOPSIS



           gcov [**-v** |**--version**] [**-h** |**--help**]
                [**-a** |**--all-blocks**]
                [**-b** |**--branch-probabilities**]
                [**-c** |**--branch-counts**]
                [**-d** |**--display-progress**]
                [**-f** |**--function-summaries**]
                [**-i** |**--json-format**]
                [**-j** |**--human-readable**]
                [**-k** |**--use-colors**]
                [**-l** |**--long-file-names**]
                [**-m** |**--demangled-names**]
                [**-n** |**--no-output**]
                [**-o** |**--object-directory** _directory|file_]
                [**-p** |**--preserve-paths**]
                [**-q** |**--use-hotness-colors**]
                [**-r** |**--relative-only**]
                [**-s** |**--source-prefix** _directory_]
                [**-t** |**--stdout**]
                [**-u** |**--unconditional-branches**]
                [**-x** |**--hash-filenames**]
                _files_
    


## DESCRIPTION



           **gcov** is a test coverage program.  Use it in concert with GCC to
           analyze your programs to help create more efficient, faster
           running code and to discover untested parts of your program.  You
           can use **gcov** as a profiling tool to help discover where your
           optimization efforts will best affect your code.  You can also use
           **gcov** along with the other profiling tool, **gprof** , to assess which
           parts of your code use the greatest amount of computing time.
    
           Profiling tools help you analyze your code's performance.  Using a
           profiler such as **gcov** or **gprof** , you can find out some basic
           performance statistics, such as:
    
           *   how often each line of code executes
    
           *   what lines of code are actually executed
    
           *   how much computing time each section of code uses
    
           Once you know these things about how your code works when
           compiled, you can look at each module to see which modules should
           be optimized.  **gcov** helps you determine where to work on
           optimization.
    
           Software developers also use coverage testing in concert with
           testsuites, to make sure software is actually good enough for a
           release.  Testsuites can verify that a program works as expected;
           a coverage program tests to see how much of the program is
           exercised by the testsuite.  Developers can then determine what
           kinds of test cases need to be added to the testsuites to create
           both better testing and a better final product.
    
           You should compile your code without optimization if you plan to
           use **gcov** because the optimization, by combining some lines of code
           into one function, may not give you as much information as you
           need to look for `hot spots' where the code is using a great deal
           of computer time.  Likewise, because **gcov** accumulates statistics
           by line (at the lowest resolution), it works best with a
           programming style that places only one statement on each line.  If
           you use complicated macros that expand to loops or to other
           control structures, the statistics are less helpful---they only
           report on the line where the macro call appears.  If your complex
           macros behave like functions, you can replace them with inline
           functions to solve this problem.
    
           **gcov** creates a logfile called _sourcefile.gcov_ which indicates how
           many times each line of a source file _sourcefile.c_ has executed.
           You can use these logfiles along with **gprof** to aid in fine-tuning
           the performance of your programs.  **gprof** gives timing information
           you can use along with the information you get from **gcov**.
    
           **gcov** works only on code compiled with GCC.  It is not compatible
           with any other profiling or test coverage mechanism.
    


## OPTIONS



           **-a**
           **--all-blocks**
               Write individual execution counts for every basic block.
               Normally gcov outputs execution counts only for the main
               blocks of a line.  With this option you can determine if
               blocks within a single line are not being executed.
    
           **-b**
           **--branch-probabilities**
               Write branch frequencies to the output file, and write branch
               summary info to the standard output.  This option allows you
               to see how often each branch in your program was taken.
               Unconditional branches will not be shown, unless the **-u** option
               is given.
    
           **-c**
           **--branch-counts**
               Write branch frequencies as the number of branches taken,
               rather than the percentage of branches taken.
    
           **-d**
           **--display-progress**
               Display the progress on the standard output.
    
           **-f**
           **--function-summaries**
               Output summaries for each function in addition to the file
               level summary.
    
           **-h**
           **--help**
               Display help about using **gcov**(on the standard output), and
               exit without doing any further processing.
    
           **-i**
           **--json-format**
               Output gcov file in an easy-to-parse JSON intermediate format
               which does not require source code for generation.  The JSON
               file is compressed with gzip compression algorithm and the
               files have _.gcov.json.gz_ extension.
    
               Structure of the JSON is following:
    
                       {
                         "current_working_directory": <current_working_directory>,
                         "data_file": <data_file>,
                         "format_version": <format_version>,
                         "gcc_version": <gcc_version>
                         "files": [<file>]
                       }
    
               Fields of the root element have following semantics:
    
               *   _current_working_directory_ : working directory where a
                   compilation unit was compiled
    
               *   _data_file_ : name of the data file (GCDA)
    
               *   _format_version_ : semantic version of the format
    
               *   _gcc_version_ : version of the GCC compiler
    
               Each _file_ has the following form:
    
                       {
                         "file": <file_name>,
                         "functions": [<function>],
                         "lines": [<line>]
                       }
    
               Fields of the _file_ element have following semantics:
    
               *   _file_name_ : name of the source file
    
               Each _function_ has the following form:
    
                       {
                         "blocks": <blocks>,
                         "blocks_executed": <blocks_executed>,
                         "demangled_name": "<demangled_name>,
                         "end_column": <end_column>,
                         "end_line": <end_line>,
                         "execution_count": <execution_count>,
                         "name": <name>,
                         "start_column": <start_column>
                         "start_line": <start_line>
                       }
    
               Fields of the _function_ element have following semantics:
    
               *   _blocks_ : number of blocks that are in the function
    
               *   _blocks_executed_ : number of executed blocks of the function
    
               *   _demangled_name_ : demangled name of the function
    
               *   _end_column_ : column in the source file where the function
                   ends
    
               *   _end_line_ : line in the source file where the function ends
    
               *   _execution_count_ : number of executions of the function
    
               *   _name_ : name of the function
    
               *   _start_column_ : column in the source file where the function
                   begins
    
               *   _start_line_ : line in the source file where the function
                   begins
    
               Note that line numbers and column numbers number from 1.  In
               the current implementation, _start_line_ and _start_column_ do not
               include any template parameters and the leading return type
               but that this is likely to be fixed in the future.
    
               Each _line_ has the following form:
    
                       {
                         "branches": [<branch>],
                         "count": <count>,
                         "line_number": <line_number>,
                         "unexecuted_block": <unexecuted_block>
                         "function_name": <function_name>,
                       }
    
               Branches are present only with _-b_ option.  Fields of the _line_
               element have following semantics:
    
               *   _count_ : number of executions of the line
    
               *   _line_number_ : line number
    
               *   _unexecuted_block_ : flag whether the line contains an
                   unexecuted block (not all statements on the line are
                   executed)
    
               *   _function_name_ : a name of a function this _line_ belongs to
                   (for a line with an inlined statements can be not set)
    
               Each _branch_ has the following form:
    
                       {
                         "count": <count>,
                         "fallthrough": <fallthrough>,
                         "throw": <throw>
                       }
    
               Fields of the _branch_ element have following semantics:
    
               *   _count_ : number of executions of the branch
    
               *   _fallthrough_ : true when the branch is a fall through branch
    
               *   _throw_ : true when the branch is an exceptional branch
    
           **-j**
           **--human-readable**
               Write counts in human readable format (like 24.6k).
    
           **-k**
           **--use-colors**
               Use colors for lines of code that have zero coverage.  We use
               red color for non-exceptional lines and cyan for exceptional.
               Same colors are used for basic blocks with **-a** option.
    
           **-l**
           **--long-file-names**
               Create long file names for included source files.  For
               example, if the header file _x.h_ contains code, and was
               included in the file _a.c_ , then running **gcov** on the file _a.c_
               will produce an output file called _a.c##x.h.gcov_ instead of
               _x.h.gcov_.  This can be useful if _x.h_ is included in multiple
               source files and you want to see the individual contributions.
               If you use the **-p** option, both the including and included file
               names will be complete path names.
    
           **-m**
           **--demangled-names**
               Display demangled function names in output. The default is to
               show mangled function names.
    
           **-n**
           **--no-output**
               Do not create the **gcov** output file.
    
           **-o** _directory|file_
           **--object-directory** _directory_
           **--object-file** _file_
               Specify either the directory containing the gcov data files,
               or the object path name.  The _.gcno_ , and _.gcda_ data files are
               searched for using this option.  If a directory is specified,
               the data files are in that directory and named after the input
               file name, without its extension.  If a file is specified
               here, the data files are named after that file, without its
               extension.
    
           **-p**
           **--preserve-paths**
               Preserve complete path information in the names of generated
               _.gcov_ files.  Without this option, just the filename component
               is used.  With this option, all directories are used, with **/**
               characters translated to **#** characters, _._ directory components
               removed and unremoveable _.._  components renamed to **^**.  This is
               useful if sourcefiles are in several different directories.
    
           **-q**
           **--use-hotness-colors**
               Emit perf-like colored output for hot lines.  Legend of the
               color scale is printed at the very beginning of the output
               file.
    
           **-r**
           **--relative-only**
               Only output information about source files with a relative
               pathname (after source prefix elision).  Absolute paths are
               usually system header files and coverage of any inline
               functions therein is normally uninteresting.
    
           **-s** _directory_
           **--source-prefix** _directory_
               A prefix for source file names to remove when generating the
               output coverage files.  This option is useful when building in
               a separate directory, and the pathname to the source directory
               is not wanted when determining the output file names.  Note
               that this prefix detection is applied before determining
               whether the source file is absolute.
    
           **-t**
           **--stdout**
               Output to standard output instead of output files.
    
           **-u**
           **--unconditional-branches**
               When branch probabilities are given, include those of
               unconditional branches.  Unconditional branches are normally
               not interesting.
    
           **-v**
           **--version**
               Display the **gcov** version number (on the standard output), and
               exit without doing any further processing.
    
           **-w**
           **--verbose**
               Print verbose informations related to basic blocks and arcs.
    
           **-x**
           **--hash-filenames**
               When using _--preserve-paths_ , gcov uses the full pathname of
               the source files to create an output filename.  This can lead
               to long filenames that can overflow filesystem limits.  This
               option creates names of the form _source-file##md5.gcov_ , where
               the _source-file_ component is the final filename part and the
               _md5_ component is calculated from the full mangled name that
               would have been used otherwise.  The option is an alternative
               to the _--preserve-paths_ on systems which have a filesystem
               limit.
    
           **gcov** should be run with the current directory the same as that
           when you invoked the compiler.  Otherwise it will not be able to
           locate the source files.  **gcov** produces files called
           _mangledname.gcov_ in the current directory.  These contain the
           coverage information of the source file they correspond to.  One
           _.gcov_ file is produced for each source (or header) file containing
           code, which was compiled to produce the data files.  The
           _mangledname_ part of the output file name is usually simply the
           source file name, but can be something more complicated if the **-l**
           or **-p** options are given.  Refer to those options for details.
    
           If you invoke **gcov** with multiple input files, the contributions
           from each input file are summed.  Typically you would invoke it
           with the same list of files as the final link of your executable.
    
           The _.gcov_ files contain the **:** separated fields along with program
           source code.  The format is
    
                   <execution_count>:<line_number>:<source line text>
    
           Additional block information may succeed each line, when requested
           by command line option.  The _execution_count_ is **-** for lines
           containing no code.  Unexecuted lines are marked **#####** or **=====** ,
           depending on whether they are reachable by non-exceptional paths
           or only exceptional paths such as C++ exception handlers,
           respectively. Given the **-a** option, unexecuted blocks are marked
           **$$$$$** or **%%%%%** , depending on whether a basic block is reachable
           via non-exceptional or exceptional paths.  Executed basic blocks
           having a statement with zero _execution_count_ end with ***** character
           and are colored with magenta color with the **-k** option.  This
           functionality is not supported in Ada.
    
           Note that GCC can completely remove the bodies of functions that
           are not needed -- for instance if they are inlined everywhere.
           Such functions are marked with **-** , which can be confusing.  Use the
           **-fkeep-inline-functions** and **-fkeep-static-functions** options to
           retain these functions and allow gcov to properly show their
           _execution_count_.
    
           Some lines of information at the start have _line_number_ of zero.
           These preamble lines are of the form
    
                   -:0:<tag>:<value>
    
           The ordering and number of these preamble lines will be augmented
           as **gcov** development progresses --- do not rely on them remaining
           unchanged.  Use _tag_ to locate a particular preamble line.
    
           The additional block information is of the form
    
                   <tag> <information>
    
           The _information_ is human readable, but designed to be simple
           enough for machine parsing too.
    
           When printing percentages, 0% and 100% are only printed when the
           values are _exactly_ 0% and 100% respectively.  Other values which
           would conventionally be rounded to 0% or 100% are instead printed
           as the nearest non-boundary value.
    
           When using **gcov** , you must first compile your program with a
           special GCC option **--coverage**.  This tells the compiler to
           generate additional information needed by gcov (basically a flow
           graph of the program) and also includes additional code in the
           object files for generating the extra profiling information needed
           by gcov.  These additional files are placed in the directory where
           the object file is located.
    
           Running the program will cause profile output to be generated.
           For each source file compiled with **-fprofile-arcs** , an accompanying
           _.gcda_ file will be placed in the object file directory.
    
           Running **gcov** with your program's source file names as arguments
           will now produce a listing of the code along with frequency of
           execution for each line.  For example, if your program is called
           _tmp.cpp_ , this is what you see when you use the basic **gcov**
           facility:
    
                   $ g++ --coverage tmp.cpp
                   $ a.out
                   $ gcov tmp.cpp -m
                   File 'tmp.cpp'
                   Lines executed:92.86% of 14
                   Creating 'tmp.cpp.gcov'
    
           The file _tmp.cpp.gcov_ contains output from **gcov**.  Here is a
           sample:
    
                           -:    0:Source:tmp.cpp
                           -:    0:Working directory:/home/gcc/testcase
                           -:    0:Graph:tmp.gcno
                           -:    0:Data:tmp.gcda
                           -:    0:Runs:1
                           -:    0:Programs:1
                           -:    1:#include <stdio.h>
                           -:    2:
                           -:    3:template<class T>
                           -:    4:class Foo
                           -:    5:{
                           -:    6:  public:
                          1*:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<char>::Foo():
                       #####:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<int>::Foo():
                           1:    7:  Foo(): b (1000) {}
                   ------------------
                          2*:    8:  void inc () { b++; }
                   ------------------
                   Foo<char>::inc():
                       #####:    8:  void inc () { b++; }
                   ------------------
                   Foo<int>::inc():
                           2:    8:  void inc () { b++; }
                   ------------------
                           -:    9:
                           -:   10:  private:
                           -:   11:  int b;
                           -:   12:};
                           -:   13:
                           -:   14:template class Foo<int>;
                           -:   15:template class Foo<char>;
                           -:   16:
                           -:   17:int
                           1:   18:main (void)
                           -:   19:{
                           -:   20:  int i, total;
                           1:   21:  Foo<int> counter;
                           -:   22:
                           1:   23:  counter.inc();
                           1:   24:  counter.inc();
                           1:   25:  total = 0;
                           -:   26:
                          11:   27:  for (i = 0; i < 10; i++)
                          10:   28:    total += i;
                           -:   29:
                          1*:   30:  int v = total > 100 ? 1 : 2;
                           -:   31:
                           1:   32:  if (total != 45)
                       #####:   33:    printf ("Failure\n");
                           -:   34:  else
                           1:   35:    printf ("Success\n");
                           1:   36:  return 0;
                           -:   37:}
    
           Note that line 7 is shown in the report multiple times.  First
           occurrence presents total number of execution of the line and the
           next two belong to instances of class Foo constructors.  As you
           can also see, line 30 contains some unexecuted basic blocks and
           thus execution count has asterisk symbol.
    
           When you use the **-a** option, you will get individual block counts,
           and the output looks like this:
    
                           -:    0:Source:tmp.cpp
                           -:    0:Working directory:/home/gcc/testcase
                           -:    0:Graph:tmp.gcno
                           -:    0:Data:tmp.gcda
                           -:    0:Runs:1
                           -:    0:Programs:1
                           -:    1:#include <stdio.h>
                           -:    2:
                           -:    3:template<class T>
                           -:    4:class Foo
                           -:    5:{
                           -:    6:  public:
                          1*:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<char>::Foo():
                       #####:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<int>::Foo():
                           1:    7:  Foo(): b (1000) {}
                   ------------------
                          2*:    8:  void inc () { b++; }
                   ------------------
                   Foo<char>::inc():
                       #####:    8:  void inc () { b++; }
                   ------------------
                   Foo<int>::inc():
                           2:    8:  void inc () { b++; }
                   ------------------
                           -:    9:
                           -:   10:  private:
                           -:   11:  int b;
                           -:   12:};
                           -:   13:
                           -:   14:template class Foo<int>;
                           -:   15:template class Foo<char>;
                           -:   16:
                           -:   17:int
                           1:   18:main (void)
                           -:   19:{
                           -:   20:  int i, total;
                           1:   21:  Foo<int> counter;
                           1:   21-block  0
                           -:   22:
                           1:   23:  counter.inc();
                           1:   23-block  0
                           1:   24:  counter.inc();
                           1:   24-block  0
                           1:   25:  total = 0;
                           -:   26:
                          11:   27:  for (i = 0; i < 10; i++)
                           1:   27-block  0
                          11:   27-block  1
                          10:   28:    total += i;
                          10:   28-block  0
                           -:   29:
                          1*:   30:  int v = total > 100 ? 1 : 2;
                           1:   30-block  0
                       %%%%%:   30-block  1
                           1:   30-block  2
                           -:   31:
                           1:   32:  if (total != 45)
                           1:   32-block  0
                       #####:   33:    printf ("Failure\n");
                       %%%%%:   33-block  0
                           -:   34:  else
                           1:   35:    printf ("Success\n");
                           1:   35-block  0
                           1:   36:  return 0;
                           1:   36-block  0
                           -:   37:}
    
           In this mode, each basic block is only shown on one line -- the
           last line of the block.  A multi-line block will only contribute
           to the execution count of that last line, and other lines will not
           be shown to contain code, unless previous blocks end on those
           lines.  The total execution count of a line is shown and
           subsequent lines show the execution counts for individual blocks
           that end on that line.  After each block, the branch and call
           counts of the block will be shown, if the **-b** option is given.
    
           Because of the way GCC instruments calls, a call count can be
           shown after a line with no individual blocks.  As you can see,
           line 33 contains a basic block that was not executed.
    
           When you use the **-b** option, your output looks like this:
    
                           -:    0:Source:tmp.cpp
                           -:    0:Working directory:/home/gcc/testcase
                           -:    0:Graph:tmp.gcno
                           -:    0:Data:tmp.gcda
                           -:    0:Runs:1
                           -:    0:Programs:1
                           -:    1:#include <stdio.h>
                           -:    2:
                           -:    3:template<class T>
                           -:    4:class Foo
                           -:    5:{
                           -:    6:  public:
                          1*:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<char>::Foo():
                   function Foo<char>::Foo() called 0 returned 0% blocks executed 0%
                       #####:    7:  Foo(): b (1000) {}
                   ------------------
                   Foo<int>::Foo():
                   function Foo<int>::Foo() called 1 returned 100% blocks executed 100%
                           1:    7:  Foo(): b (1000) {}
                   ------------------
                          2*:    8:  void inc () { b++; }
                   ------------------
                   Foo<char>::inc():
                   function Foo<char>::inc() called 0 returned 0% blocks executed 0%
                       #####:    8:  void inc () { b++; }
                   ------------------
                   Foo<int>::inc():
                   function Foo<int>::inc() called 2 returned 100% blocks executed 100%
                           2:    8:  void inc () { b++; }
                   ------------------
                           -:    9:
                           -:   10:  private:
                           -:   11:  int b;
                           -:   12:};
                           -:   13:
                           -:   14:template class Foo<int>;
                           -:   15:template class Foo<char>;
                           -:   16:
                           -:   17:int
                   function main called 1 returned 100% blocks executed 81%
                           1:   18:main (void)
                           -:   19:{
                           -:   20:  int i, total;
                           1:   21:  Foo<int> counter;
                   call    0 returned 100%
                   branch  1 taken 100% (fallthrough)
                   branch  2 taken 0% (throw)
                           -:   22:
                           1:   23:  counter.inc();
                   call    0 returned 100%
                   branch  1 taken 100% (fallthrough)
                   branch  2 taken 0% (throw)
                           1:   24:  counter.inc();
                   call    0 returned 100%
                   branch  1 taken 100% (fallthrough)
                   branch  2 taken 0% (throw)
                           1:   25:  total = 0;
                           -:   26:
                          11:   27:  for (i = 0; i < 10; i++)
                   branch  0 taken 91% (fallthrough)
                   branch  1 taken 9%
                          10:   28:    total += i;
                           -:   29:
                          1*:   30:  int v = total > 100 ? 1 : 2;
                   branch  0 taken 0% (fallthrough)
                   branch  1 taken 100%
                           -:   31:
                           1:   32:  if (total != 45)
                   branch  0 taken 0% (fallthrough)
                   branch  1 taken 100%
                       #####:   33:    printf ("Failure\n");
                   call    0 never executed
                   branch  1 never executed
                   branch  2 never executed
                           -:   34:  else
                           1:   35:    printf ("Success\n");
                   call    0 returned 100%
                   branch  1 taken 100% (fallthrough)
                   branch  2 taken 0% (throw)
                           1:   36:  return 0;
                           -:   37:}
    
           For each function, a line is printed showing how many times the
           function is called, how many times it returns and what percentage
           of the function's blocks were executed.
    
           For each basic block, a line is printed after the last line of the
           basic block describing the branch or call that ends the basic
           block.  There can be multiple branches and calls listed for a
           single source line if there are multiple basic blocks that end on
           that line.  In this case, the branches and calls are each given a
           number.  There is no simple way to map these branches and calls
           back to source constructs.  In general, though, the lowest
           numbered branch or call will correspond to the leftmost construct
           on the source line.
    
           For a branch, if it was executed at least once, then a percentage
           indicating the number of times the branch was taken divided by the
           number of times the branch was executed will be printed.
           Otherwise, the message "never executed" is printed.
    
           For a call, if it was executed at least once, then a percentage
           indicating the number of times the call returned divided by the
           number of times the call was executed will be printed.  This will
           usually be 100%, but may be less for functions that call "exit" or
           "longjmp", and thus may not return every time they are called.
    
           The execution counts are cumulative.  If the example program were
           executed again without removing the _.gcda_ file, the count for the
           number of times each line in the source was executed would be
           added to the results of the previous run(s).  This is potentially
           useful in several ways.  For example, it could be used to
           accumulate data over a number of program runs as part of a test
           verification suite, or to provide more accurate long-term
           information over a large number of program runs.
    
           The data in the _.gcda_ files is saved immediately before the
           program exits.  For each source file compiled with **-fprofile-arcs** ,
           the profiling code first attempts to read in an existing _.gcda_
           file; if the file doesn't match the executable (differing number
           of basic block counts) it will ignore the contents of the file.
           It then adds in the new execution counts and finally writes the
           data to the file.
    
       **Using gcov with GCC Optimization**
           If you plan to use **gcov** to help optimize your code, you must first
           compile your program with a special GCC option **--coverage**.  Aside
           from that, you can use any other GCC options; but if you want to
           prove that every single line in your program was executed, you
           should not compile with optimization at the same time.  On some
           machines the optimizer can eliminate some simple code lines by
           combining them with other lines.  For example, code like this:
    
                   if (a != b)
                     c = 1;
                   else
                     c = 0;
    
           can be compiled into one instruction on some machines.  In this
           case, there is no way for **gcov** to calculate separate execution
           counts for each line because there isn't separate code for each
           line.  Hence the **gcov** output looks like this if you compiled the
           program with optimization:
    
                         100:   12:if (a != b)
                         100:   13:  c = 1;
                         100:   14:else
                         100:   15:  c = 0;
    
           The output shows that this block of code, combined by
           optimization, executed 100 times.  In one sense this result is
           correct, because there was only one instruction representing all
           four of these lines.  However, the output does not indicate how
           many times the result was 0 and how many times the result was 1.
    
           Inlineable functions can create unexpected line counts.  Line
           counts are shown for the source code of the inlineable function,
           but what is shown depends on where the function is inlined, or if
           it is not inlined at all.
    
           If the function is not inlined, the compiler must emit an out of
           line copy of the function, in any object file that needs it.  If
           _fileA.o_ and _fileB.o_ both contain out of line bodies of a
           particular inlineable function, they will also both contain
           coverage counts for that function.  When _fileA.o_ and _fileB.o_ are
           linked together, the linker will, on many systems, select one of
           those out of line bodies for all calls to that function, and
           remove or ignore the other.  Unfortunately, it will not remove the
           coverage counters for the unused function body.  Hence when
           instrumented, all but one use of that function will show zero
           counts.
    
           If the function is inlined in several places, the block structure
           in each location might not be the same.  For instance, a condition
           might now be calculable at compile time in some instances.
           Because the coverage of all the uses of the inline function will
           be shown for the same source lines, the line counts themselves
           might seem inconsistent.
    
           Long-running applications can use the "__gcov_reset" and
           "__gcov_dump" facilities to restrict profile collection to the
           program region of interest. Calling "__gcov_reset(void)" will
           clear all profile counters to zero, and calling
           "__gcov_dump(void)" will cause the profile information collected
           at that point to be dumped to _.gcda_ output files.  Instrumented
           applications use a static destructor with priority 99 to invoke
           the "__gcov_dump" function. Thus "__gcov_dump" is executed after
           all user defined static destructors, as well as handlers
           registered with "atexit".  If an executable loads a dynamic shared
           object via dlopen functionality, **-Wl,--dynamic-list-data** is needed
           to dump all profile data.
    
           Profiling run-time library reports various errors related to
           profile manipulation and profile saving.  Errors are printed into
           standard error output or **GCOV_ERROR_FILE** file, if environment
           variable is used.  In order to terminate immediately after an
           errors occurs set **GCOV_EXIT_AT_ERROR** environment variable.  That
           can help users to find profile clashing which leads to a
           misleading profile.
    


* * *