How do I write a C header file that can be used in C++ programs? [duplicate]

Answer 1

You might find it reasonable to define three macros to help with this:

#ifdef __cplusplus
#define EXTERN_C_BEGIN extern "C" {
#define EXTERN_C_END   }
#define EXTERN_C       extern "C"
#else
#define EXTERN_C_BEGIN /* Nothing */
#define EXTERN_C_END   /* Nothing */
#define EXTERN_C       extern /* Or Nothing */
#endif /* __cplusplus */

This would be most useful in a standard header that's included in most places in your project. For a single function, you might write:

EXTERN_C size_t insert(const char *name);

For a group of functions, you might write:

EXTERN_C_BEGIN

size_t other_insert(const char *name);
size_t other_delete(const char *name);
size_t other_update(const char *old_name, const char *new_name);

EXTERN_C_END

It is permissible to include extern in front of the individual functions inside the EXTERN_C_BEGIN to EXTERN_C_END block.

Answer 2

It is normal to bracket C header files as follows so they can be used in C++ programs. Check your system header files such as stdio.h and you will probably see this:

#ifdef __cplusplus
extern "C" {
#endif

...

#ifdef __cplusplus
}
#endif

Answer 3

The answer is to use the macro __cplusplus. In this instance, the most straightforward approach is:

extern
#ifdef __cplusplus
"C"
#endif
size_t insert (const char*);

This macro is part of the C++ standard.