Example

static void foo(){
printf("foo is not called in this file");
}


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

Solution
Make use of the static function or remove it from the  file.

static void foo(){
printf("foo is not called in this file");
}


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