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.
8 .\" Redistribution and use in source and binary forms, with or without
9 .\" modification, are permitted provided that the following conditions
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12 .\" notice, this list of conditions and the following disclaimer.
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18 .\" This product includes software developed by the University of
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20 .\" 4. Neither the name of the University nor the names of its contributors
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24 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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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 2001-06-09 "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
60 .BI ", size_t " size );
63 The three types of buffering available are unbuffered, block buffered, and
64 line buffered. When an output stream is unbuffered, information appears on
65 the destination file or terminal as soon as written; when it is block
66 buffered many characters are saved up and written as a block; when it is
67 line buffered characters are saved up until a newline is output or input is
68 read from any stream attached to a terminal device (typically stdin). The
71 may be used to force the block out early.
74 Normally all files are block buffered. When the first I/O operation occurs
77 is called, and a buffer is obtained. If a stream refers to a terminal (as
79 normally does) it is line buffered. The standard error stream
81 is always unbuffered by default.
85 function may be used on any open stream to change its buffer.
88 parameter must be one of the following three macros:
101 Except for unbuffered files, the
103 argument should point to a buffer at least
105 bytes long; this buffer will be used instead of the current buffer. If the
110 only the mode is affected; a new buffer will be allocated on the next read
111 or write operation. The
113 function may only be used after opening a stream and before any other
114 operations have been performed on it.
116 The other three calls are, in effect, simply aliases for calls to
120 function is exactly equivalent to the call
123 setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
128 function is the same, except that the size of the buffer is up to the
129 caller, rather than being determined by the default
133 function is exactly equivalent to the call:
136 setvbuf(stream, (char *)NULL, _IOLBF, 0);
141 returns 0 on success.
142 It can return any value on failure, but returns nonzero when
144 is invalid or the request cannot be honoured. It may set
147 The other functions are void.
153 functions conform to ANSI X3.159-1989 (``ANSI C'').
159 functions are not portable to versions of BSD before 4.2BSD, and
160 are available under Linux since libc 4.5.21. On 4.2BSD and 4.3BSD systems,
162 always uses a suboptimal buffer size and should be avoided.
164 You must make sure that both
166 and the space it points to still exist by the time
168 is closed, which also happens at program termination.
170 For example, the following is illegal:
178 printf("Hello, world!\\n");