Code Coverage with gcov

Purpose

Instrument C/C++ programs with gcov to measure test coverage.

How It Works

Build with Coverage

bash
gcc --coverage -o program source.c

Run Program

bash
./program
# Creates .gcda files with execution data

Generate Reports

Text report:

bash
gcov source.c
# Creates source.c.gcov with line-by-line coverage

HTML report:

bash
gcovr --html-details -o coverage.html

Coverage Flags

• --coverage (shorthand for -fprofile-arcs -ftest-coverage -lgcov)
• Add to both CFLAGS and LDFLAGS

Build System Integration

Makefile

makefile
ENABLE_COVERAGE ?= 0
ifeq ($(ENABLE_COVERAGE),1)
    CFLAGS += --coverage
    LDFLAGS += --coverage
endif

CMake

cmake
option(ENABLE_COVERAGE "Enable coverage" OFF)
if(ENABLE_COVERAGE)
    add_compile_options(--coverage)
    add_link_options(--coverage)
endif()

When User Requests Coverage

Steps

1. Detect build system (Makefile/CMake/other)
2. Add --coverage to CFLAGS and LDFLAGS
3. Clean previous build: make clean or rm -f *.gcda *.gcno
4. Build with coverage: make ENABLE_COVERAGE=1 or cmake -DENABLE_COVERAGE=ON
5. Run tests: make test or ./test_suite
6. Generate report: gcovr --html-details coverage.html --print-summary
7. Present summary and path to HTML report

Output

Text (.gcov files):

        -:    0:Source:main.c
        5:   42:    int x = 10;
    #####:   43:    unused_code();

• 5: = executed 5 times
• #####: = not executed
• -: = non-executable

HTML: Interactive report with color-coded coverage

Metrics

• Line coverage: Executed lines / total lines
• Branch coverage: Taken branches / total branches
• Function coverage: Called functions / total functions

Target: 80%+ line coverage, 70%+ branch coverage