PHP Manual . ... PHP 3 <= 3.0.18, PHP 4 >= 4.0.0) fwrite -- Binary-safe file write . int fwrite ( int fp, string string [, int length]) . ... If the length argument is given, writing will stop after length bytes have been written or the end of string is reached, whichever comes first. fwrite() returns the number of bytes written, or -1 on error. ... Note: On systems which differentiate between binary and text files (i.e. Windows) the file must be opened with 'b' included in fopen() mode parameter. ...