how to get the size of a byte buffer

Code:

DPError		dpResult		=  DPMS_SUCCESS;
    FILE		*hFile			= NULL;
	BOOL		bRetValue		= FALSE;
	CDPString   dpFilePath;
	size_t      size            = 0;
	char       *tBuffer		= new char[m_sFileSize];
	tBuffer = m_pszStream;


	dpFilePath   = m_dpFilePath;
	dpFilePath   += "\\";
	dpFilePath   += m_dpFileName;	
    
	if(hFile == NULL)
	{
		hFile = fopen(dpFilePath, "a+");
		if(hFile)
		{
			size = fwrite(m_pszStream, m_sFileSize,sizeof(char), hFile);			
			if(size < 0)
			{
				dpResult = DPMS_FILE_WRITE_ERROR;
			}
            fclose(hFile);
		}
		else
		{
		   dpResult = DPMS_FILE_OPEN_ERROR;
		}		
	}	
	
	return dpResult;
}

in this code i had made size of file as member variable but i want it to access through the char* type of buffer. this char* could contain any type of data like binary string so the size should be for binary data also.