引用MSDN上的内容,具体也没用过..
ofstream( filedesc fd, char* pch, int nLength );
fd
A file descriptor as returned by a call to the run-time function _open or _sopen; filedesc is a typedef equivalent to int.
pch
Pointer to a previously allocated reserve area of length nLength. A NULL value (or nLength = 0) indicates that the stream will be unbuffered.
nLength
The length (in bytes) of the reserve area (0 = unbuffered).