path: root/devdocs/gcc~13/invoking-gcov.html

<div class="section-level-extent" id="Invoking-Gcov"> <div class="nav-panel"> <p> Next: <a href="gcov-and-optimization" accesskey="n" rel="next">Using <code class="command">gcov</code> with GCC Optimization</a>, Previous: <a href="gcov-intro" accesskey="p" rel="prev">Introduction to <code class="command">gcov</code></a>, Up: <a href="gcov" accesskey="u" rel="up"><code class="command">gcov</code>—a Test Coverage Program</a> [<a href="index#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="indices" title="Index" rel="index">Index</a>]</p> </div>  <h1 class="section" id="Invoking-gcov"><span>10.2 Invoking gcov<a class="copiable-link" href="#Invoking-gcov"> ¶</a></span></h1> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">gcov <span class="r">[</span><var class="var">options</var><span class="r">]</span> <var class="var">files</var></pre>
</div> <p><code class="command">gcov</code> accepts the following options: </p> <dl class="table"> <dt><code class="code">-a</code></dt> <dt><code class="code">--all-blocks</code></dt> <dd>
<p>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. </p> </dd> <dt><code class="code">-b</code></dt> <dt><code class="code">--branch-probabilities</code></dt> <dd>
<p>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 <samp class="option">-u</samp> option is given. </p> </dd> <dt><code class="code">-c</code></dt> <dt><code class="code">--branch-counts</code></dt> <dd>
<p>Write branch frequencies as the number of branches taken, rather than the percentage of branches taken. </p> </dd> <dt><code class="code">-d</code></dt> <dt><code class="code">--display-progress</code></dt> <dd>
<p>Display the progress on the standard output. </p> </dd> <dt><code class="code">-f</code></dt> <dt><code class="code">--function-summaries</code></dt> <dd>
<p>Output summaries for each function in addition to the file level summary. </p> </dd> <dt><code class="code">-h</code></dt> <dt><code class="code">--help</code></dt> <dd>
<p>Display help about using <code class="command">gcov</code> (on the standard output), and exit without doing any further processing. </p> </dd> <dt><code class="code">-j</code></dt> <dt><code class="code">--json-format</code></dt> <dd>
<p>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 <samp class="file">.gcov.json.gz</samp> extension. </p> <p>Structure of the JSON is following: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">{
  "current_working_directory": "foo/bar",
  "data_file": "a.out",
  "format_version": "1",
  "gcc_version": "11.1.1 20210510"
  "files": ["$file"]
}</pre>
</div> <p>Fields of the root element have following semantics: </p> <ul class="itemize mark-bullet"> <li>
<var class="var">current_working_directory</var>: working directory where a compilation unit was compiled </li>
<li>
<var class="var">data_file</var>: name of the data file (GCDA) </li>
<li>
<var class="var">format_version</var>: semantic version of the format </li>
<li>
<var class="var">gcc_version</var>: version of the GCC compiler </li>
</ul> <p>Each <var class="var">file</var> has the following form: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">{
  "file": "a.c",
  "functions": ["$function"],
  "lines": ["$line"]
}</pre>
</div> <p>Fields of the <var class="var">file</var> element have following semantics: </p> <ul class="itemize mark-bullet"> <li>
<var class="var">file_name</var>: name of the source file </li>
</ul> <p>Each <var class="var">function</var> has the following form: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">{
  "blocks": 2,
  "blocks_executed": 2,
  "demangled_name": "foo",
  "end_column": 1,
  "end_line": 4,
  "execution_count": 1,
  "name": "foo",
  "start_column": 5,
  "start_line": 1
}</pre>
</div> <p>Fields of the <var class="var">function</var> element have following semantics: </p> <ul class="itemize mark-bullet"> <li>
<var class="var">blocks</var>: number of blocks that are in the function </li>
<li>
<var class="var">blocks_executed</var>: number of executed blocks of the function </li>
<li>
<var class="var">demangled_name</var>: demangled name of the function </li>
<li>
<var class="var">end_column</var>: column in the source file where the function ends </li>
<li>
<var class="var">end_line</var>: line in the source file where the function ends </li>
<li>
<var class="var">execution_count</var>: number of executions of the function </li>
<li>
<var class="var">name</var>: name of the function </li>
<li>
<var class="var">start_column</var>: column in the source file where the function begins </li>
<li>
<var class="var">start_line</var>: line in the source file where the function begins </li>
</ul> <p>Note that line numbers and column numbers number from 1. In the current implementation, <var class="var">start_line</var> and <var class="var">start_column</var> do not include any template parameters and the leading return type but that this is likely to be fixed in the future. </p> <p>Each <var class="var">line</var> has the following form: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">{
  "branches": ["$branch"],
  "count": 2,
  "line_number": 15,
  "unexecuted_block": false,
  "function_name": "foo",
}</pre>
</div> <p>Branches are present only with <var class="var">-b</var> option. Fields of the <var class="var">line</var> element have following semantics: </p> <ul class="itemize mark-bullet"> <li>
<var class="var">count</var>: number of executions of the line </li>
<li>
<var class="var">line_number</var>: line number </li>
<li>
<var class="var">unexecuted_block</var>: flag whether the line contains an unexecuted block (not all statements on the line are executed) </li>
<li>
<var class="var">function_name</var>: a name of a function this <var class="var">line</var> belongs to (for a line with an inlined statements can be not set) </li>
</ul> <p>Each <var class="var">branch</var> has the following form: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">{
  "count": 11,
  "fallthrough": true,
  "throw": false
}</pre>
</div> <p>Fields of the <var class="var">branch</var> element have following semantics: </p> <ul class="itemize mark-bullet"> <li>
<var class="var">count</var>: number of executions of the branch </li>
<li>
<var class="var">fallthrough</var>: true when the branch is a fall through branch </li>
<li>
<var class="var">throw</var>: true when the branch is an exceptional branch </li>
</ul> </dd> <dt><code class="code">-H</code></dt> <dt><code class="code">--human-readable</code></dt> <dd>
<p>Write counts in human readable format (like 24.6k). </p> </dd> <dt><code class="code">-k</code></dt> <dt><code class="code">--use-colors</code></dt> <dd> <p>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 <samp class="option">-a</samp> option. </p> </dd> <dt><code class="code">-l</code></dt> <dt><code class="code">--long-file-names</code></dt> <dd>
<p>Create long file names for included source files. For example, if the header file <samp class="file">x.h</samp> contains code, and was included in the file <samp class="file">a.c</samp>, then running <code class="command">gcov</code> on the file <samp class="file">a.c</samp> will produce an output file called <samp class="file">a.c##x.h.gcov</samp> instead of <samp class="file">x.h.gcov</samp>. This can be useful if <samp class="file">x.h</samp> is included in multiple source files and you want to see the individual contributions. If you use the ‘<samp class="samp">-p</samp>’ option, both the including and included file names will be complete path names. </p> </dd> <dt><code class="code">-m</code></dt> <dt><code class="code">--demangled-names</code></dt> <dd>
<p>Display demangled function names in output. The default is to show mangled function names. </p> </dd> <dt><code class="code">-n</code></dt> <dt><code class="code">--no-output</code></dt> <dd>
<p>Do not create the <code class="command">gcov</code> output file. </p> </dd> <dt><code class="code">-o <var class="var">directory|file</var></code></dt> <dt><code class="code">--object-directory <var class="var">directory</var></code></dt> <dt><code class="code">--object-file <var class="var">file</var></code></dt> <dd>
<p>Specify either the directory containing the gcov data files, or the object path name. The <samp class="file">.gcno</samp>, and <samp class="file">.gcda</samp> 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> </dd> <dt><code class="code">-p</code></dt> <dt><code class="code">--preserve-paths</code></dt> <dd>
<p>Preserve complete path information in the names of generated <samp class="file">.gcov</samp> files. Without this option, just the filename component is used. With this option, all directories are used, with ‘<samp class="samp">/</samp>’ characters translated to ‘<samp class="samp">#</samp>’ characters, <samp class="file">.</samp> directory components removed and unremoveable <samp class="file">..</samp> components renamed to ‘<samp class="samp">^</samp>’. This is useful if sourcefiles are in several different directories. </p> </dd> <dt><code class="code">-q</code></dt> <dt><code class="code">--use-hotness-colors</code></dt> <dd> <p>Emit perf-like colored output for hot lines. Legend of the color scale is printed at the very beginning of the output file. </p> </dd> <dt><code class="code">-r</code></dt> <dt><code class="code">--relative-only</code></dt> <dd>
<p>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. </p> </dd> <dt><code class="code">-s <var class="var">directory</var></code></dt> <dt><code class="code">--source-prefix <var class="var">directory</var></code></dt> <dd>
<p>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. </p> </dd> <dt><code class="code">-t</code></dt> <dt><code class="code">--stdout</code></dt> <dd>
<p>Output to standard output instead of output files. </p> </dd> <dt><code class="code">-u</code></dt> <dt><code class="code">--unconditional-branches</code></dt> <dd>
<p>When branch probabilities are given, include those of unconditional branches. Unconditional branches are normally not interesting. </p> </dd> <dt><code class="code">-v</code></dt> <dt><code class="code">--version</code></dt> <dd>
<p>Display the <code class="command">gcov</code> version number (on the standard output), and exit without doing any further processing. </p> </dd> <dt><code class="code">-w</code></dt> <dt><code class="code">--verbose</code></dt> <dd>
<p>Print verbose informations related to basic blocks and arcs. </p> </dd> <dt><code class="code">-x</code></dt> <dt><code class="code">--hash-filenames</code></dt> <dd>
<p>When using <var class="var">–preserve-paths</var>, 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 <samp class="file"><var class="var">source-file</var>##<var class="var">md5</var>.gcov</samp>, where the <var class="var">source-file</var> component is the final filename part and the <var class="var">md5</var> component is calculated from the full mangled name that would have been used otherwise. The option is an alternative to the <var class="var">–preserve-paths</var> on systems which have a filesystem limit. </p> </dd> </dl> <p><code class="command">gcov</code> 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. <code class="command">gcov</code> produces files called <samp class="file"><var class="var">mangledname</var>.gcov</samp> in the current directory. These contain the coverage information of the source file they correspond to. One <samp class="file">.gcov</samp> file is produced for each source (or header) file containing code, which was compiled to produce the data files. The <var class="var">mangledname</var> part of the output file name is usually simply the source file name, but can be something more complicated if the ‘<samp class="samp">-l</samp>’ or ‘<samp class="samp">-p</samp>’ options are given. Refer to those options for details. </p> <p>If you invoke <code class="command">gcov</code> 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. </p> <p>The <samp class="file">.gcov</samp> files contain the ‘<samp class="samp">:</samp>’ separated fields along with program source code. The format is </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp"><var class="var">execution_count</var>:<var class="var">line_number</var>:<var class="var">source line text</var></pre>
</div> <p>Additional block information may succeed each line, when requested by command line option. The <var class="var">execution_count</var> is ‘<samp class="samp">-</samp>’ for lines containing no code. Unexecuted lines are marked ‘<samp class="samp">#####</samp>’ or ‘<samp class="samp">=====</samp>’, depending on whether they are reachable by non-exceptional paths or only exceptional paths such as C++ exception handlers, respectively. Given the ‘<samp class="samp">-a</samp>’ option, unexecuted blocks are marked ‘<samp class="samp">$$$$$</samp>’ or ‘<samp class="samp">%%%%%</samp>’, depending on whether a basic block is reachable via non-exceptional or exceptional paths. Executed basic blocks having a statement with zero <var class="var">execution_count</var> end with ‘<samp class="samp">*</samp>’ character and are colored with magenta color with the <samp class="option">-k</samp> option. This functionality is not supported in Ada. </p> <p>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 ‘<samp class="samp">-</samp>’, which can be confusing. Use the <samp class="option">-fkeep-inline-functions</samp> and <samp class="option">-fkeep-static-functions</samp> options to retain these functions and allow gcov to properly show their <var class="var">execution_count</var>. </p> <p>Some lines of information at the start have <var class="var">line_number</var> of zero. These preamble lines are of the form </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">-:0:<var class="var">tag</var>:<var class="var">value</var></pre>
</div> <p>The ordering and number of these preamble lines will be augmented as <code class="command">gcov</code> development progresses — do not rely on them remaining unchanged. Use <var class="var">tag</var> to locate a particular preamble line. </p> <p>The additional block information is of the form </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp"><var class="var">tag</var> <var class="var">information</var></pre>
</div> <p>The <var class="var">information</var> is human readable, but designed to be simple enough for machine parsing too. </p> <p>When printing percentages, 0% and 100% are only printed when the values are <em class="emph">exactly</em> 0% and 100% respectively. Other values which would conventionally be rounded to 0% or 100% are instead printed as the nearest non-boundary value. </p> <p>When using <code class="command">gcov</code>, you must first compile your program with a special GCC option ‘<samp class="samp">--coverage</samp>’. 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. </p> <p>Running the program will cause profile output to be generated. For each source file compiled with <samp class="option">-fprofile-arcs</samp>, an accompanying <samp class="file">.gcda</samp> file will be placed in the object file directory. </p> <p>Running <code class="command">gcov</code> 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 <samp class="file">tmp.cpp</samp>, this is what you see when you use the basic <code class="command">gcov</code> facility: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">$ g++ --coverage tmp.cpp -c
$ g++ --coverage tmp.o
$ a.out
$ gcov tmp.cpp -m
File 'tmp.cpp'
Lines executed:92.86% of 14
Creating 'tmp.cpp.gcov'</pre>
</div> <p>The file <samp class="file">tmp.cpp.gcov</samp> contains output from <code class="command">gcov</code>. Here is a sample: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">-:    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 &lt;stdio.h&gt;
        -:    2:
        -:    3:template&lt;class T&gt;
        -:    4:class Foo
        -:    5:{
        -:    6:  public:
       1*:    7:  Foo(): b (1000) {}
------------------
Foo&lt;char&gt;::Foo():
    #####:    7:  Foo(): b (1000) {}
------------------
Foo&lt;int&gt;::Foo():
        1:    7:  Foo(): b (1000) {}
------------------
       2*:    8:  void inc () { b++; }
------------------
Foo&lt;char&gt;::inc():
    #####:    8:  void inc () { b++; }
------------------
Foo&lt;int&gt;::inc():
        2:    8:  void inc () { b++; }
------------------
        -:    9:
        -:   10:  private:
        -:   11:  int b;
        -:   12:};
        -:   13:
        -:   14:template class Foo&lt;int&gt;;
        -:   15:template class Foo&lt;char&gt;;
        -:   16:
        -:   17:int
        1:   18:main (void)
        -:   19:{
        -:   20:  int i, total;
        1:   21:  Foo&lt;int&gt; counter;
        -:   22:
        1:   23:  counter.inc();
        1:   24:  counter.inc();
        1:   25:  total = 0;
        -:   26:
       11:   27:  for (i = 0; i &lt; 10; i++)
       10:   28:    total += i;
        -:   29:
       1*:   30:  int v = total &gt; 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:}</pre>
</div> <p>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. </p> <p>When you use the <samp class="option">-a</samp> option, you will get individual block counts, and the output looks like this: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">-:    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 &lt;stdio.h&gt;
        -:    2:
        -:    3:template&lt;class T&gt;
        -:    4:class Foo
        -:    5:{
        -:    6:  public:
       1*:    7:  Foo(): b (1000) {}
------------------
Foo&lt;char&gt;::Foo():
    #####:    7:  Foo(): b (1000) {}
------------------
Foo&lt;int&gt;::Foo():
        1:    7:  Foo(): b (1000) {}
------------------
       2*:    8:  void inc () { b++; }
------------------
Foo&lt;char&gt;::inc():
    #####:    8:  void inc () { b++; }
------------------
Foo&lt;int&gt;::inc():
        2:    8:  void inc () { b++; }
------------------
        -:    9:
        -:   10:  private:
        -:   11:  int b;
        -:   12:};
        -:   13:
        -:   14:template class Foo&lt;int&gt;;
        -:   15:template class Foo&lt;char&gt;;
        -:   16:
        -:   17:int
        1:   18:main (void)
        -:   19:{
        -:   20:  int i, total;
        1:   21:  Foo&lt;int&gt; 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 &lt; 10; i++)
        1:   27-block  0
       11:   27-block  1
       10:   28:    total += i;
       10:   28-block  0
        -:   29:
       1*:   30:  int v = total &gt; 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:}</pre>
</div> <p>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 <samp class="option">-b</samp> option is given. </p> <p>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. </p> <p>When you use the <samp class="option">-b</samp> option, your output looks like this: </p> <div class="example smallexample"> <pre class="example-preformatted" data-language="cpp">-:    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 &lt;stdio.h&gt;
        -:    2:
        -:    3:template&lt;class T&gt;
        -:    4:class Foo
        -:    5:{
        -:    6:  public:
       1*:    7:  Foo(): b (1000) {}
------------------
Foo&lt;char&gt;::Foo():
function Foo&lt;char&gt;::Foo() called 0 returned 0% blocks executed 0%
    #####:    7:  Foo(): b (1000) {}
------------------
Foo&lt;int&gt;::Foo():
function Foo&lt;int&gt;::Foo() called 1 returned 100% blocks executed 100%
        1:    7:  Foo(): b (1000) {}
------------------
       2*:    8:  void inc () { b++; }
------------------
Foo&lt;char&gt;::inc():
function Foo&lt;char&gt;::inc() called 0 returned 0% blocks executed 0%
    #####:    8:  void inc () { b++; }
------------------
Foo&lt;int&gt;::inc():
function Foo&lt;int&gt;::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&lt;int&gt;;
        -:   15:template class Foo&lt;char&gt;;
        -:   16:
        -:   17:int
function main called 1 returned 100% blocks executed 81%
        1:   18:main (void)
        -:   19:{
        -:   20:  int i, total;
        1:   21:  Foo&lt;int&gt; 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 &lt; 10; i++)
branch  0 taken 91% (fallthrough)
branch  1 taken 9%
       10:   28:    total += i;
        -:   29:
       1*:   30:  int v = total &gt; 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:}</pre>
</div> <p>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. </p> <p>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. </p> <p>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. </p> <p>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 <code class="code">exit</code> or <code class="code">longjmp</code>, and thus may not return every time they are called. </p> <p>The execution counts are cumulative. If the example program were executed again without removing the <samp class="file">.gcda</samp> 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. </p> <p>The data in the <samp class="file">.gcda</samp> files is saved immediately before the program exits. For each source file compiled with <samp class="option">-fprofile-arcs</samp>, the profiling code first attempts to read in an existing <samp class="file">.gcda</samp> 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. </p> </div>  <div class="nav-panel"> <p> Next: <a href="gcov-and-optimization">Using <code class="command">gcov</code> with GCC Optimization</a>, Previous: <a href="gcov-intro">Introduction to <code class="command">gcov</code></a>, Up: <a href="gcov"><code class="command">gcov</code>—a Test Coverage Program</a> [<a href="index#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="indices" title="Index" rel="index">Index</a>]</p> </div><div class="_attribution">
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