Question

In a C project, I have a main() function in several files. When I compile I thus have an error “multiple declarations of main”. Is it possible to choose in the Makefile which one of those main() functions should be used to compile ? (the other ones would then be ignored…)

Answer 1

You could hide them using the pre-processor:

In file1.c:

#if defined FILE1_MAIN
int main(void)
{
  printf("Running main() in file1.c");
  return 0;
}
#endif

This can be repeated as necessary in any number of C files.

Then have logic in the Makefile that passes the proper -D option to the compiler, i.e. -DFILE1_MAIN to include the main() from file1, -DFILE2_MAIN to get file2.c’s, and so on.

This technique can also be useful when implementing e.g. library modules, to include an optional main() for testing in a single C file.