gcov [-b] [-v] [-n] [-l] [-f] [-o directory] sourcefile

• -b
Write branch frequencies to the output file. Write branch summary info to standard output. This option allows you to see how often each branch was taken.
• -v
Display the gcov version number (on the standard error stream).
• -n
Do not create the gcov output file.
• -l
Create long filenames 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 ‘a.c.x.h.gcov’ instead of ‘x.h.gcov’. This can be useful if ‘x.h’ is included in multiple source files.
• -f
Output summaries for each function in addition to the file level summary.
• -o
The directory where the object files live. gcov will search for ‘.bb’, ‘.bbg’, and ‘.da’ files in this directory.

Running gcov will cause profile output to be generated. For each source file compiled with -fprofile-arcs, and accompanying file, .da, will be placed in the source directory.

Running gcov with your program’s source file names as arguments will now produce a listing of the code along with frquency of execution for each line. For example, if your program is called ‘tmp.c’, you’ll see the following when you use the gcov facility.

For example, if your program is called ‘tmp.c’, the following is what you see when you use the basic gcov facility.

$ gcc -fprofile-arcs -ftest-coverage tmp.c 
$ a.out 
$ gcov tmp.c 
  87.50% of 8 source lines executed in file tmp.c 
Creating tmp.c.gcov.

         main() 
         { 
        1    int i, total; 

        1    total = 0; 
       11    for (i = 0; i < 10; i++) 
       10    total += i; 
        1    if (total != 45) 
######         printf ("Failure\n"); 
         else 
        1    printf ("Success\n"); 
        1    }

call 0 returns = 100% 
          1 }

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, 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 .da 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 .da 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 .da 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.