OSX C++ Export function

Question

I got a large C++ project that uses a makefile on OSX. where I simply want to add an exported function that I can resolve can call. The project needs to be an executeable and not a library. It already exports a bunch of functions but I cannot get my export to work, meaning it's not visible when I run nm on the binary.

I tried to simply add this to the header .h

#define EXPORT __attribute__((visibility("default")))
EXPORT int callme(int test);

I also tried declaring it in the header like

EXPORT int callme(int test) {return 0;}

but then i get a bunch of errors of the symbol already existing in other object files.

Edit: It's a simple C function and I also tried

 #if !defined(__cplusplus)
 #define MONExternC extern
 #else
 #define MONExternC extern "C"
 #endif

 MONExternC int callme (int test);

I'm a bit of novice when it comes to C++ and any insight or help would be much appreciated, thanks.

Answer 1

You have defined (not just declared) a standalone, non-member, non-template, non-inline function in a header. This is exactly the thing you should not be doing. It leads to the sort of errors you describe, and is prohibited by the standard.

You should have only a function ptototype in the header. Move its definition to an exactly one source file.

The visibility attribute only makes sense when building shared libraries. You probably don't need it.