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:}
+

+ +

Notes

gcov(1)

Example