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36 .\" @(#)setbuf.3 8.1 (Berkeley) 6/4/93
47 .Nd stream buffering operations
49 .Fd #include <stdio.h>
51 .Fn setbuf "FILE *stream" "char *buf"
53 .Fn setbuffer "FILE *stream" "char *buf" "int size"
55 .Fn setlinebuf "FILE *stream"
57 .Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size"
59 The three types of buffering available are unbuffered, block buffered,
61 When an output stream is unbuffered, information appears on the
62 destination file or terminal as soon as written;
63 when it is block buffered many characters are saved up and written as a block;
64 when it is line buffered characters are saved up until a newline is
65 output or input is read from any stream attached to a terminal device
69 may be used to force the block out early.
73 Normally all files are block buffered.
76 operation occurs on a file,
79 and an optimally-sized buffer is obtained.
80 If a stream refers to a terminal
83 normally does) it is line buffered.
84 The standard error stream
91 may be used to alter the buffering behavior of a stream.
94 parameter must be one of the following three macros:
95 .Bl -tag -width _IOFBF -offset indent
106 parameter may be given as zero
107 to obtain deferred optimal-size buffer allocation as usual.
109 then except for unbuffered files, the
111 argument should point to a buffer at least
114 this buffer will be used instead of the current buffer.
122 a buffer of the given size will be allocated immediately,
123 and released on close.
124 This is an extension to ANSI C;
125 portable code should use a size of 0 with any
131 function may be used at any time,
132 but may have peculiar side effects
133 (such as discarding input or flushing output)
134 if the stream is ``active''.
135 Portable applications should call it only once on any given stream,
140 The other three calls are, in effect, simply aliases for calls to
142 Except for the lack of a return value, the
144 function is exactly equivalent to the call
146 .Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
151 is the same, except that the size of the buffer is up to the caller,
152 rather than being determined by the default
157 is exactly equivalent to the call:
159 .Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);"
163 function returns 0 on success, or
165 if the request cannot be honored
166 (note that the stream is still functional in this case).
170 function returns what the equivalent
193 functions are not portable to versions of
203 always uses a suboptimal buffer size and should be avoided.