1 .\" Copyright (c) 1980, 1991 Regents of the University of California.
2 .\" All rights reserved.
4 .\" This code is derived from software contributed to Berkeley by
5 .\" the American National Standards Committee X3, on Information
6 .\" Processing Systems.
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36 .\" @(#)setbuf.3 6.10 (Berkeley) 6/29/91
38 .\" Converted for Linux, Mon Nov 29 14:55:24 1993, faith@cs.unc.edu
39 .\" Added section to BUGS, Sun Mar 12 22:28:33 MET 1995,
40 .\" Thomas.Koenig@ciw.uni-karlsruhe.de
41 .\" Correction, Sun, 11 Apr 1999 15:55:18,
42 .\" Martin Vicente <martin@netadmin.dgac.fr>
43 .\" Correction, 2000-03-03, Andreas Jaeger <aj@suse.de>
44 .\" Added return value for setvbuf, aeb,
46 .TH SETBUF 3 2008-06-26 "Linux" "Linux Programmer's Manual"
48 setbuf, setbuffer, setlinebuf, setvbuf \- stream buffering operations
53 .BI "void setbuf(FILE *" stream ", char *" buf );
55 .BI "void setbuffer(FILE *" stream ", char *" buf ", size_t " size );
57 .BI "void setlinebuf(FILE *" stream );
59 .BI "int setvbuf(FILE *" stream ", char *" buf ", int " mode \
64 Feature Test Macro Requirements for glibc (see
65 .BR feature_test_macros (7)):
72 The three types of buffering available are unbuffered, block buffered, and
74 When an output stream is unbuffered, information appears on
75 the destination file or terminal as soon as written; when it is block
76 buffered many characters are saved up and written as a block; when it is
77 line buffered characters are saved up until a newline is output or input is
78 read from any stream attached to a terminal device (typically \fIstdin\fP).
81 may be used to force the block out early.
84 Normally all files are block buffered.
85 When the first I/O operation occurs on a file,
87 is called, and a buffer is obtained.
88 If a stream refers to a terminal (as
90 normally does) it is line buffered.
91 The standard error stream
93 is always unbuffered by default.
97 function may be used on any open stream to change its buffer.
100 argument must be one of the following three macros:
113 Except for unbuffered files, the
115 argument should point to a buffer at least
117 bytes long; this buffer will be used instead of the current buffer.
121 only the mode is affected; a new buffer will be allocated on the next read
125 function may only be used after opening a stream and before any other
126 operations have been performed on it.
128 The other three calls are, in effect, simply aliases for calls to
132 function is exactly equivalent to the call
135 setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
140 function is the same, except that the size of the buffer is up to the
141 caller, rather than being determined by the default
145 function is exactly equivalent to the call:
148 setvbuf(stream, (char *) NULL, _IOLBF, 0);
153 returns 0 on success.
154 It returns nonzero on failure
156 is invalid or the request cannot be honored).
161 The other functions do not return a value.
167 functions conform to C89 and C99.
173 functions are not portable to versions of BSD before 4.2BSD, and
174 are available under Linux since libc 4.5.21.
175 On 4.2BSD and 4.3BSD systems,
177 always uses a suboptimal buffer size and should be avoided.
179 You must make sure that the space that
181 points to still exists by the time
183 is closed, which also happens at program termination.
184 For example, the following is invalid:
194 printf("Hello, world!\\n");