SETBUF(S) UNIX System V SETBUF(S)
Name
setbuf, setvbuf - assign buffering to a stream
Syntax
#include <stdio.h>
void setbuf (stream, buf)
FILE *stream;
char *buf;
int setvbuf (stream, buf, type, size)
FILE *stream;
char *buf;
int type, size;
Description
The setbuf function may be used after a stream has been
opened but before it is read or written. It causes the
array pointed to by buf to be used instead of an
automatically allocated buffer. If buf is the NULL pointer,
input/output will be completely unbuffered.
A constant BUFSIZ, defined in the <stdio.h> header file,
tells how big an array is needed:
char buf[BUFSIZ];
setvbuf may be used after a stream has been opened but
before it is read or written. Type determines how stream
will be buffered. Legal values for type (defined in
stdio.h) are:
_IOFBF causes input/output to be fully buffered.
_IOLBF causes output to be line buffered; the buffer will
be flushed when a newline is written, the buffer is
full, or input is requested.
_IONBF causes input/output to be completely unbuffered.
If buf is not the NULL pointer, the array it points to will
be used for buffering, instead of an automatically allocated
buffer. size specifies the size of the buffer to be used.
The constant BUFSIZ in <stdio.h> is suggested as a good
buffer size. If input/output is unbuffered, buf and size
are ignored.
By default, output to a terminal is line-buffered and all
other input/output is fully buffered.
See Also
fopen(S), getc(S), malloc(S), putc(S), stdio(S)
Diagnostics
If an illegal value for type or size is provided, setvbuf
returns a non-zero value. Otherwise, the value returned will
be zero.
Notes
A common source of error is allocating buffer space as an
``automatic'' variable in a code block, and then failing to
close the stream in the same block.
The parameter order of the setvbuf function is altered by
the -compat option of the cc(CP) command.
Standards Conformance
setbuf is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
The X/Open Portability Guide II of January 1987;
ANSI X3.159-198X C Language Draft Standard, May 13,
1988;
IEEE POSIX Std 1003.1-1988 with C Standard Language-
Dependent System Support;
and NIST FIPS 151-1.
setvbuf is conformant with:
AT&T SVID Issue 2, Select Code 307-127;
The X/Open Portability Guide II of January 1987;
and ANSI X3.159-198X C Language Draft Standard, May 13,
1988.
(printed 6/20/89)