NAME
    gcov - coverage testing tool

SYNOPSIS
    gcov [-v|--version] [-h|--help]
   [-b|--branch-probabilities] [-c|--branch-counts]
   [-n|--no-output] [-l|--long-file-names]
   [-f|--function-summaries]
   [-o|--object-directory directory] sourcefile

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. You
    can use gcov as a profiling tool to help discover where your optimiza-
    tion 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 pro-
    filer such as gcov or gprof, you can find out some basic performance
    statistics, such as:

    o  how often each line of code executes

    o  what lines of code are actually executed

    o  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 test-
    suites, to make sure software is actually good enough for a release.
    Testsuites can verify that a program works as expected; a coverage pro-
    gram tests to see how much of the program is exercised by the test-
    suite. 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 help-
    ful---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 perfor-
    mance 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
    -h
    --help
   Display help about using gcov (on the standard output), and exit
   without doing any further processing.

    -v
    --version
   Display the gcov version number (on the standard output), and exit
   without doing any further processing.

    -b
    --branch-probabilities
   Write branch frequencies to the output file, and write branch sum-
   mary info to the standard output. This option allows you to see
   how often each branch in your program was taken.

    -c
    --branch-counts
   Write branch frequencies as the number of branches taken, rather
   than the percentage of branches taken.

    -n
    --no-output
   Do not create the gcov output file.

    -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.

    -f
    --function-summaries
   Output summaries for each function in addition to the file level
   summary.

    -o directory
    --object-directory directory
   The directory where the object files live. Gcov will search for
   .bb, .bbg, and .da files in this directory.

    When using gcov, you must first compile your program with two special
    GCC options: -fprofile-arcs -ftest-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 source
    code is located.

    Running the program will cause profile output to be generated. For
    each source file compiled with -fprofile-arcs, an accompanying .da file
    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 frequency of execution for
    each line. For example, if your program is called tmp.c, this 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.

    The file tmp.c.gcov contains output from gcov. Here is a sample:

       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  }

    When you use the -b option, your output looks like this:

     $ gcov -b tmp.c
  87.50% of 8 source lines executed in file tmp.c
  80.00% of 5 branches executed in file tmp.c
  80.00% of 5 branches taken at least once in file tmp.c
  50.00% of 2 calls executed in file tmp.c
     Creating tmp.c.gcov.

    Here is a sample of a resulting tmp.c.gcov file:

       main()
       {
    1  int i, total;

    1  total = 0;

    11  for (i = 0; i < 10; i++)
     branch 0 taken = 91%
     branch 1 taken = 100%
     branch 2 taken = 100%
    10   total += i;

    1  if (total != 45)
     branch 0 taken = 100%
     ######   printf ("Failure\n");
     call 0 never executed
     branch 1 never executed
     else
    1   printf ("Success\n");
     call 0 returns = 100%
    1  }

    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 sim-
    ple 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 indi-
    cating the number of times the branch was taken divided by the number
    of times the branch was executed will be printed. Otherwise, the mes-
    sage ``never executed'' is printed.

    For a call, if it was executed at least once, then a percentage indi-
    cating 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 call "exit" or "longjmp", and thus
    may not return every time they are called.

    The execution counts are cumulative. If the example program were exe-
    cuted 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 profil-
    ing 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 exe-
    cution 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 com-
    pile your program with two special GCC options: -fprofile-arcs
    -ftest-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 optimiza-
    tion:

     100 if (a != b)
     100  c = 1;
     100 else
     100  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. How-
    ever, the output does not indicate how many times the result was 0 and
    how many times the result was 1.

SEE ALSO
    gpl(7),gfdl(7), fsf-funding(7),gcc(1) and the Info entry for gcc.

COPYRIGHT
    Copyright (c) 1996, 1997, 1999, 2000, 2001 Free Software Foundation,
    Inc.

    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.1 or
    any later version published by the Free Software Foundation; with the
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    Free Software'', the Front-Cover texts being (a) (see below), and with
    the Back-Cover Texts being (b) (see below). A copy of the license is
    included in thegfdl(7) man page.

    (a) The FSF's Front-Cover Text is:

   A GNU Manual

    (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
   software. Copies published by the Free Software Foundation raise
   funds for GNU development.