Wrapping a C lib with extern "C" except an internal C++ include

Question

I have a C library that I need to use in a C++ code, so I need to wrap the whole lib with an extern "C" block. The problem is that the library seems to include a C++ compiled code, so wrapping the whole lib would also wrap that C++ header.

Inside lib.h I only include all the internal headers I want to expose, something like this:

#ifndef LIB_H
#define LIB_H

#include "lib_foo.h"
#include "lib_bar.h"
#include "lib_baz.h"

#endif

So the client will only need to include lib.h to use the lib.

In my first attempt I've done this:

#ifndef LIB_H
#define LIB_H

extern "C" {
  #include "lib_foo.h"
  #include "lib_bar.h"
  #include "lib_baz.h"
}

#endif

But then I get a symbol lookup error when I execute any function inside already_compiled_c++.h.

How can I avoid from applying extern "C" in the already_compiled_c++.h header file?

---

Edit:

Solved. This was not a problem using extern "C", it was a problem linking the compiled c++ library with gyp correctly: Using shared library in Gyp in node-sqlite3

Answer 1

Note that extern C isn't legal C, so it must only be included hen compiling as C++.

The already_compiled_c++.h header probably contains a guard against multiple includes, so just include it first:

#ifndef LIB_H
#define LIB_H

# This include added so that it won't get marked extern "C" when included by lob_foo.h.
#include <already_compiled_c++.h>

#ifdef __cplusplus
extern "C" {
#endif

  #include "lib_foo.h"
  #include "lib_bar.h"
  #include "lib_baz.h"

#ifdef __cplusplus
}
#endif

#endif

Note: You need to check if already_compiled_c++.h is conditionally included and add the corresponding conditionals.