file_ptr A pointer to a file. buffer A pointer to a character array, or a NULL pointer. type The buffering type. Use one of the following values defined in <stdio.h>: _IOFBF or _IOLBF. size The number of bytes to be used in buffer by the C RTL for buffering this file. The buffer size must be a minimum of 8192 bytes and a maximum of 32767 bytes.