gcov

Additional Notes

gcov is a code coverage analysis tool that works with programs compiled by GCC. It reports how many times each line of source code was executed during a test run. It is used to identify untested code paths and measure test coverage.

To use gcov, compile your program with special flags (-fprofile-arcs -ftest-coverage), run the program to generate coverage data files (.gcda), then run gcov on the source files. The output shows execution counts per line, highlighting which lines were never executed.

Syntax

gcov [options] source-file...

Parameters

• source-file: The source code file to analyze (e.g., file.c).

Common Options

• -a, --all-blocks: Show information for every basic block, not just executed lines.
• -b, --branch-probabilities: Include branch probability statistics.
• -c, --branch-counts: Show branch counts instead of percentages.
• -f, --function-summaries: Show coverage summary for each function.
• -i, --intermediate-format: Output data in an intermediate text format for further processing.
• -l, --long-file-names: Use long output filenames for header files.
• -n, --no-output: Do not create output files.
• -o directory|file, --object-directory directory|file: Specify the directory containing the .gcda and .gcno data files.
• -p, --preserve-paths: Preserve original source path structure in output.
• -r, --relative-only: Show only coverage data relative to the current directory.
• -s directory, --source-prefix directory: Strip the specified prefix from source file paths.
• -u, --unconditional-branches: Include unconditional branches in branch statistics.
• -v, --version: Show version information.

Examples

gcc -fprofile-arcs -ftest-coverage program.c -o program
./program
gcov program.c

Compile with coverage instrumentation, run the program, and analyze coverage.

gcov -b program.c

Include branch probability information in the coverage report.

gcov -f program.c

Show per-function coverage summaries.

gcov -o build/ program.c

Specify a different directory for the coverage data files.

Practical Notes

• The source file must be compiled with -fprofile-arcs -ftest-coverage. Linking with -lgcov or --coverage is also recommended.
• The first run with instrumentation creates .gcno files. Each program execution updates .gcda files.
• The output is a .gcov file alongside the source, showing line counts prefixed in the left column.
• Running the same program multiple times accumulates coverage data in the .gcda files.
• For modern workflows, consider gcovr or lcov which provide HTML reports and summary output.
• The --coverage compiler flag is a shortcut that enables both -fprofile-arcs and -ftest-coverage.