How to get gcov results for included C/CPP files

Question

I'm trying to get gcov results on a file that's brought in via #include. If I compile with it as a separate object file it works fine. For example with these files:

lib.h

int addFive(int num);

lib.c

#include "lib.h"
int addFive(int num)
{
   return num + 5;
}

testlib.cpp

#include "lib.h"
int main()
{
   return addFive(2);
}

If I then compile like so:

g++ -c -fprofile-arcs -ftest-coverage lib.c -o lib.o
g++ -c testlib.cpp -o testlib.o
g++ lib.o testlib.o -lgcov -o testlib

then I will get a gcda file as expected:

[~]$ strings testlib | grep gcda
/home/user/lib.gcda
[~]$

But if I attempt this when including the .c file like below

test.cpp

#include "lib.c"
int main()
{
   return addFive(2);
}

And compile that

g++ test.cpp -lgcov -o test

Then I don't get the gcda as expected:

[~]$ strings test | grep gcda
[~]$

Is there a way to get the gcda to show up when including a C file? The same applies to including a .cpp.

Answer 1

If I compile test with --coverage instead of -lgcov it does generate a test.gcda. I thought at first this was not what I wanted since I'm looking for coverage in lib.c

But if I run both testlib and test and then use gcov on all the files together, it combines the coverage data properly:

gcov lib.gcda lib.gcno test.gcda test.gcno

And this yields lib.c.gcov with code coverage from both test runs.