setbuf, setvbuf - assign buffering to a stream
void setbuf(FILE *stream, char *buf);
int setvbuf(FILE *stream, char *buf, int type, size_t size);
The setbuf() function may be used after the stream pointed
to by stream (see intro(3)) is 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.
The constant BUFSIZ, defined in the <stdio.h> header, indi-
cates the size of the array pointed to by buf.
The setvbuf() function may be used after a stream is opened
but before it is read or written. The type argument deter-
mines how stream will be buffered. Legal values for type
(defined in <stdio.h>) are:
Input/output to be fully buffered.
Output to be line buffered; the buffer will be
flushed when a NEWLINE is written, the buffer is full,
or input is requested.
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. The size argument specifies the size of the buffer
to be used. If input/output is unbuffered, buf and size
For a further discussion of buffering, see stdio(3C).
If an illegal value for type is provided, setvbuf() returns
a non-zero value. Otherwise, it returns 0.
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.
When using setbuf(), buf should always be sized using BUF-
SIZ. If the array pointed to by buf is larger than BUFSIZ, a
portion of buf will not be used. If buf is smaller than
BUFSIZ, other memory may be unexpectedly overwritten.
Parts of buf will be used for internal bookkeeping of the
stream and, therefore, buf will contain less than size bytes
when full. It is recommended that stdio(3C) be used to han-
dle buffer allocation when using setvbuf().
See attributes(5) for descriptions of the following attri-
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | MT-Safe |
fopen(3C), getc(3C), malloc(3C), putc(3C), stdio(3C), attri-
Man(1) output converted with