Using C code from C++ using autotools

Question

I am writing a (my first) C++ class on top of some code written in C, but I can only get the C++ to compile by declaring the C functions in a extern block. My project uses autotools; is there any way to automate this process so I don't have to maintain two header files?

Answer 1

Yes create wrapper header files which include your C header files like so...

//Wrapper.h
#ifdef __cplusplus
extern "C"
{

    #include "Actual.h"
}
#else
    #include "Actual.h"
#endif


//Use.cpp
#include "Wrapper.h"

int main()
{
    return 0;
}

//Use.c
#include "Wrapper.h"
/*or #include "Actual.h" */

int main()
{
    return 0;
}

Answer 2

Use a extern block inside a #ifdef in C codes header files

Start of header files

#ifdef __cplusplus
extern "C" {
#endif

...and at end of the header files

#ifdef __cplusplus
}
#endif

This way it will work for being included in both C and C++ sources

Answer 3

Use the C Preprocessor. Do something like this:

 #ifdef __cplusplus
 extern "C" {
 #endif 
// code goes here

#ifdef __cplusplus
}
#endif

Answer 4

We have a macro in a header file:

#ifdef __cplusplus
    #define _crtn "C"
#else
    #define _crtn
#endif

Then in header files, we can use _crtn:

#include "croutine.h"

extern _crtn void MyFunction( ... );

The only gotcha is to make sure you include the header file containing the prototype of MyFunction inside the file containing the implementation of MyFunction so that it is compiled with "C" linkage.

This is the same as @epatel's answer, but only requires the ugly #ifdef's in one header file.