setbuf(3S) SDK R4.11 setbuf(3S)
NAME
setbuf, setvbuf - assign buffering to a stream
SYNOPSIS
#include <stdio.h>
void setbuf (FILE *stream, char *buf);
int setvbuf (FILE *stream, char *buf, int type, sizet size);
DESCRIPTION
setbuf may be used after a stream [see intro(3)] 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.
setbuf can also be used after a stream has been opened and written to
if the buffer has been flushed with fflush prior to calling setbuf.
[See fopen(3S)]. This will prevent loss of data in the existing
buffer.
To use setbuf after a read, make sure that the application has read
all of the characters in one buffer and make sure that it will not
receive any more characters until after calling setbuf.
While there is no limitation on the size of the buffer, the constant
BUFSIZ, defined in the stdio.h header file, is typically a good
buffer size (except in the case of setbuf - it is the only allowed
size):
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. Valid
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 is 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 is used for
buffering, instead of an automatically allocated buffer. size
specifies the size of the buffer to be used. If input/output is
unbuffered, buf and size are ignored.
For a further discussion of buffering, see stdio(3S).
Errors
If an invalid value for type is provided, setvbuf returns a non-zero
value. Otherwise, it returns zero.
Considerations for Threads Programming
+---------+-----------------------------+
| | async- |
|function | reentrant cancel cancel |
| | point safe |
+---------+-----------------------------+
|setbuf | Y N N |
|setvbuf | Y N N |
+---------+-----------------------------+
REFERENCES
reentrant(3), malloc(3C), fopen(3S), getc(3S), putc(3S), stdio(3S)
NOTICES
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.
Parts of buf are used for internal bookkeeping of the stream and,
therefore, buf contains less than size bytes when full. It is
recommended that the automatically allocated buffer is used when
using setvbuf.
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