VC++ : how to hook/unhook API ReadFile

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C++

VC9.0

Hi,
We are hooking ReadFile methods GLOBALLY .

CAPIHook g_ReadFile; //the main object of CAPIHook! 
typedef bool (WINAPI *PFNReadFile)( 
__in HANDLE hFile, 
__out LPVOID lpBuffer, 
__in DWORD nNumberOfBytesToRea 
__out LPDWORD lpNumberOfBytesRead 
__in LPOVERLAPPED lpOverlapped ); 
bool WINAPI MyReadFile( 
__in HANDLE hFile, 
__out LPVOID lpBuffer, 
__in DWORD nNumberOfBytesToRead, 
__out LPDWORD lpNumberOfBytesRead, 
__in LPOVERLAPPED lpOverlapped ) 
{ 
char * m_pBuf = (char *)"zxcvzxcv"; //The problem is here, how to write my own data into the Buffer,and displayed it out?
DWORD len = 0;
nResult = ((PFNReadFile)(PROC)g_ReadFile)(hFile, m_pBuf, strlen(m_pBuf), &len, NULL); 
return nResult; 
} 

This will produce garbage! How to modify?

Please provide help.
Thank you