C inline function used from C++ code

Question

I am trying to call an inline function defined in C from C++ code and I am getting an unresolved symbol error. Can I even do this?

In def.h:

#ifdef __cplusplus
extern "C" {
#endif

#include "types.h"


extern inline void foo();


#ifdef __cplusplus
}
#endif /* extern "C" */

In def.c:

inline void foo()
{
    some code
}

Elsewhere in c++ code:

void bar()
{
    foo();
}

And this is where I get an unresolved symbol error. Is there a way to make this compile? And if so, how will it work? Will the compiler replace the function call in my C++ code by the C definition? Eliminating functional calls is important as this is for an embedded environment.

Thank you.

Answer 1

Most compilers generate code on source file level; to generate code, the compiler must "see" the source of all functions for which it needs to generate code. Unless you have LTO/LTGC, you have to make the source of all inline functions available in every file where they are called.

Try moving the source of the inlined function(s) into the corresponding header:

def.h:

#ifdef __cplusplus
extern "C" {
#endif

#include "types.h"

inline void foo()
{
   some code
}

#ifdef __cplusplus
}
#endif /* extern "C" */

def.c:

Remove foo() definition from this file (or remove this file).

Elsewhere in c++ code:

#include "def.h"

void bar()
{
    foo();
}