gcov

gcov is a test coverage tool that ships with the GNU Compiler Collection (GCC). It analyzes how much of a C or C++ program’s source code is exercised by a set of tests, helping developers identify untested or under-tested code paths. gcov works by using instrumentation added by the compiler during compilation and by processing profiling data collected at run time.

When a program is compiled with coverage instrumentation, GCC generates additional data files during execution. Compiling typically uses flags such as -fprofile-arcs and -ftest-coverage to enable branch and line coverage data collection. Running the instrumented program creates .gcda and .gcno files that record execution information. After tests have run, gcov is invoked on the corresponding source file to produce a human-readable report, often in the form of a .gcov file that shows per-line execution counts and, if branch data was collected, branch information as well.

Usage generally follows a pattern: compile with coverage flags, run the program to generate profiling data, then run gcov on the source file (and optionally use -b for branch data). The resulting reports highlight executed lines with counts and can be complemented by tools like gcovr or lcov to produce summaries or HTML reports.

gcov is part of GCC and is commonly used in conjunction with other coverage tooling to aggregate results across multiple files or test runs. Limitations include reliance on instrumentation at compile time, potential changes in coverage accuracy with optimizations, and the need to retain source and debug information to interpret the reports effectively.