gcov(1)

Generate code coverage reports in text format.

Compile the source files of interest and link the final binary with the following flags:

• -fprofile-arcs instruments the generated code such that it writes a .gcda file when being executed with details about which branches are taken
• -ftest-coverage writes a .gcno notes file which is used by gcov during generation of the coverage report

Depending on the build environment one may also set -fprofile-abs-path to generate absolute path names into the .gcno note files, this can ease setups where compilations are done in different directories to the source directory.

gcc / clang also support an alias flag --coverage which during compilation time is equivalent to -fprofile-arcs -ftest-coverage and during link time -lgcov.

After running the instrumented binary, the human readable report can then be generated for a single file for example such as

gcov <SRC FILE | OBJ FILE>

Example

#include <cstdio>

void tell_me(int desc) {
  if (desc & 1) {
    std::puts("this");
  } else {
    std::puts("that");
  }
}

int main(int argc, char *argv[]) {
  tell_me(argc);
  tell_me(argc);
  return 0;
}

The gcov coverage report can be generated as follows for gcc or clang.

CXXFLAGS = -fprofile-arcs -ftest-coverage
# or the alias
#CXXFLAGS = --coverage

cov-gcc: clean
	g++ $(CXXFLAGS) -c -o cov.o cov.cc
	g++ $(CXXFLAGS) -o $@ cov.o
	./$@
	gcov --demangled-names cov.cc
	cat cov.cc.gcov
.PHONY: cov-gcc

cov-clang: clean
	clang++ $(CXXFLAGS) -c -o cov.o cov.cc
	clang++ $(CXXFLAGS) -o $@ cov.o
	./$@
	llvm-cov gcov --demangled-names cov.cc
	cat cov.cc.gcov
.PHONY: cov-clang

clean:
	$(RM) *.gcov *.gcno *.gcda *.o cov-*

The will generate a report similar to the following.

cat cov.cc.gcov
        -:    0:Source:cov.cc
        -:    0:Graph:cov.gcno
        -:    0:Data:cov.gcda
        -:    0:Runs:1
        -:    1:// Copyright (C) 2023 johannst
        -:    2:
        -:    3:#include <cstdio>
        -:    4:
        2:    5:void tell_me(int desc) {
        2:    6:  if (desc & 1) {
        2:    7:    std::puts("this");
        -:    8:  } else {
    #####:    9:    std::puts("that");
        -:   10:  }
        2:   11:}
        -:   12:
        1:   13:int main(int argc, char *argv[]) {
        1:   14:  tell_me(argc);
        1:   15:  tell_me(argc);
        1:   16:  return 0;
        -:   17:}