macro definition containing #include directive

Question

Is there a way to define a macro that contains a #include directive in its body?

If I just put the \"#include\", it gives the error

Answer 1

I also wanted to do this, and here's the reason:

Some header files (notably mpi.h in OpenMPI) work differently if you are compiling in C or C++. I'm linking to a C MPI code from my C++ program. To include the header, I do the usual:

extern "C" {
#include "blah.h"
}

But this doesn't work because __cplusplus is still defined even in C linkage. That means mpi.h, which is included by blah.h, starts defining templates and the compiler dies saying you can't use templates with C linkage.

Hence, what I have to do in blah.h is to replace

#include 

with

#ifdef __cplusplus
#undef __cplusplus
#include 
#define __cplusplus
#else
#include 
#endif

Remarkably it's not just mpi.h that does this pathological thing. Hence, I want to define a macro INCLUDE_AS_C which does the above for the specified file. But I guess that doesn't work.

If anyone can figure out another way of accomplishing this, please let me know.