113 lines
2.7 KiB
Groff
113 lines
2.7 KiB
Groff
.\" Copyright (c) 1980 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)setbuf.3s 6.2 (Berkeley) 5/12/86
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.\"
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.TH SETBUF 3 "May 12, 1986"
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.UC 4
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.SH NAME
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setbuf, setvbuf \- assign buffering to a stream
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.SH SYNOPSIS
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.nf
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.ft B
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#include <stdio.h>
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int setbuf(FILE *\fIstream\fP, char *\fIbuf\fP)
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int setvbuf(FILE *\fIstream\fP, char *\fIbuf\fP, int \fItype\fP, size_t \fIsize\fP)
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.SH DESCRIPTION
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The three types of buffering available are unbuffered, block buffered,
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and line buffered.
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When an output stream is unbuffered, information appears on the
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destination file or terminal as soon as written;
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when it is block buffered many characters are saved up and written as a block;
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when it is line buffered characters are saved up until a newline is
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encountered or input is read from stdin.
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.B Fflush
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(see
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.BR fclose (3))
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may be used to force the block out early.
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Normally all files are block buffered.
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A buffer is obtained from
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.BR malloc (3)
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upon the first
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.B getc
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or
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.BR putc (3)
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on the file.
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If the standard stream
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.B stdout
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refers to a terminal it is line buffered.
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The standard stream
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.B stderr
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is always unbuffered.
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.PP
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.B Setbuf
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is used after a stream has been opened but before it is read or written.
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The character array
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.I buf
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is used instead of an automatically allocated buffer. If
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.I buf
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is the constant pointer
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.SM
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.BR NULL ,
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input/output will be completely unbuffered.
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A manifest constant
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.SM
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.B BUFSIZ
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tells how big an array is needed:
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.IP
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.B char
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buf[BUFSIZ];
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.PP
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.BR Setvbuf ,
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an alternate form of
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.BR setbuf ,
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is used after a stream has been opened but before it is read or written.
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It has three uses, depending on the value of the
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.IR type
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argument:
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.TP 5
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.B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOFBF, \fIsize\fP)"
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Causes input/output to be fully buffered using the character array
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.I buf
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whose size is determined by the
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.I size
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argument.
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If
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.I buf
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is the constant pointer
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.SM
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.BR NULL ,
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then an automatically allocated buffer will be used.
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.TP 5
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.B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOLBF, \fIsize\fP)"
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Like above, except that output will be line buffered, i.e. the buffer will
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be flushed when a newline is written, the buffer is full, or input is
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requested.
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.TP 5
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.B "setvbuf(\fIstream\fP, \fIbuf\fP, _IONBF, \fIsize\fP)"
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Causes input/output to be completely unbuffered.
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.I Buf
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and
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.I size
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are ignored.
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.PP
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A file can be changed between unbuffered, line buffered, or block buffered
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by using
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.B freopen
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(see
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.BR fopen (3))
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followed by the appropriate
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.B setvbuf
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call.
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.SH "SEE ALSO"
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.BR fopen (3),
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.BR getc (3),
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.BR putc (3),
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.BR malloc (3),
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.BR fclose (3),
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.BR puts (3),
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.BR printf (3),
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.BR fread (3).
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