Exporting C Functions for Use in C or C++ Language Executables

If you have functions in a DLL written in C that you want to access from a C language or C++ language module, you should use the __cplusplus preprocessor macro to determine which language is being compiled, and then declare these functions with C linkage if being used from a C++ language module. If you use this technique and provide header files for your DLL, these functions can be used by C and C++ users with no change.

The following code shows a header file that can be used by C and C++ client applications:

// MyCFuncs.h
#ifdef __cplusplus
extern "C" {  // only need to export C interface if
              // used by C++ source code

__declspec( dllimport ) void MyCFunc();
__declspec( dllimport ) void AnotherCFunc();

#ifdef __cplusplus

If you need to link C functions to your C++ executable and the function declaration header files have not used the above technique, in the C++ source file, do the following to prevent the compiler from decorating the C function names:

extern "C" {
#include "MyCHeader.h"

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See also

Exporting from a DLL