setbuf - assign buffering to stream

Syntax	#include <stdio.h> void setbuf(FILE *stream, char *buf);
Description	setbuf() may be used after the stream pointed to by stream has been assigned to an open file but before any other operation has been performed on the stream. It causes the array pointed to by buf to be used instead of an automatically allocated buffer. The buffer size is not limited; however, the constant BUFSIZ (see stdio.h) is typically a good buffer size: char buf[BUFSIZ]; If buf is not a null pointer, the following function calls are equivalent: setbuf(stream, buf) setvbuf(stream, buf, _IOFBF, BUFSIZ) If buf is a null pointer, input and output are unbuffered, and the following calls are equivalent: setbuf(stream, buf) setvbuf(stream, buf, _IONBF, BUFSIZ) BS2000 If buf is a null pointer, the buffer assigned by the system is used. (End) In contrast to setvbuf(), setbuf() has no return value.
Notes	A common source of error is to use an "automatic" variable (i.e. a variable of storage class auto) as the buffer in a program block and then fail to close the file in the same block. Since a portion of buf is required for internal administration data of the stream, buf will contain less than size bytes when full. It is therefore preferable to use setvbuf() with automatically assigned buffers. setbuf() is executed for the file assigned to stream. This can be a POSIX file or a BS2000 file. BS2000 If the blocking factor is explicitly defined with the BUFFER-LENGTH parameter of the SET-FILE-LINK command, the size of the area must correspond to this defined blocking size. (End)
See also	fopen(), setvbuf(), stdio.h, section “Streams”.