how to call function in c# written in c++ dll

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VS2008

C#

Visual-Studio

I have xyz.dll and two header file xyz.hpp and ErrorCode.h
In xyz.hpp

#define  FC3_PR_VERSION   "Version" 
typedef void *  FC3_t 
typedef FC3_t  FC3Template_t  
typedef FC3_t  FC3Encode_t  
typedef FC3_t  FC3Match_t  
typedef void DRMAPI  ProgressCallBack_t
(int nPercentCompleted, void *const pUserData) 

abcErrorCode_t FC3Initialize (const char *szReserved) 
abcErrorCode_t FC3Uninitialize (void) 
abcErrorCode_t FC3CreateTemplate (FC3Template_t *const pTemplateHandle) 
abcErrorCode_t FC3CreateEncoder (FC3Encode_t *const pEncodeHandle) 
abcErrorCode_t FC3Encode (const FC3Encode_t hEncodeHandle, const BITMAPINFOHEADER *const pBitmapData, const size_t nBitmapSize, const FC3Template_t hTemplate) 
abcErrorCode_t FC3CreateMatcher (FC3Match_t *const pMatchHandle) 
abcErrorCode_t FC3DestroyHandle (FC3_t *const pHandle)
abcErrorCode_t FC3Match (const FC3Match_t hMatchHandle, const FC3Template_t hTemplate1, const FC3Template_t hTemplate2, double *const pdScore)  

and in ErrorCode.h

#define FPC_SUCCESS   0
#define  FPC_ERROR_INITIALIZED   -1 
#define  FPC_ERROR_NOT_INITIALIZED   -2 
#define  FPC_ERROR_NO_LICENCE   -3 
#define  FPC_ERROR_NO_CB_ONEND   -4 
#define  FPC_ERROR_NO_CB_ONERROR   -5 
#define  FPC_ERROR_CODING_LOGGED   -6 
#define  FPC_ERROR_BITMAP_PTR   -10 
#define  FPC_ERROR_BITMAP_COMPRESSION   -31 
#define  FPC_ERROR_BITMAP_HEADERSIZE   -32 
#define  FPC_ERROR_BITMAP_UNEXPECTED_FILEHEADER   -36 

typedef long abcErrorCode_t 

I want to call these functions in c#(help me).