how to use C++ _Stcall with structure used in C# project in window application

#ifdef __cplusplus
extern "C"
{
#endif

typedef long (__stdcall *DATADETECTEDPROC)(const unsigned char *pData, unsigned long ulSize, void *pContext);
typedef struct _FN_CONTEXT
{
	unsigned long ulFlags;
	DATADETECTEDPROC pfnDataDetected;
	void *pContext;
} FN_CONTEXT, *PFN_CONTEXT;
typedef const FN_CONTEXT *PCFN_CONTEXT;

long __stdcall InitCommContext(PCFN_CONTEXT pContext);
long __stdcall ExitCommContext();

#ifdef __cplusplus
}
#endif