The checksum is stored in 4 bytes at the end of a file. The "p_" stands for "parameter" to indicate it's a parameter from a function's sight. It is a pointer though, I indicated that with "lpsz" (long pointer to a zero terminated string).
Actually I'm just trying out some naming conventions and other coding styles lately (I am busy with C and C++ for about one year now).
I want to read 4 bytes from the 'p_lpszFileData' variable which is of type 'const char * '.