1SETBUF(3) Library Functions Manual SETBUF(3)
2
6 setbuf, setbuffer, setlinebuf, setvbuf -stream buffering operations
7
9 #include <stdio.h>
10 #include <sys/types.h>
11 void
13 setbuf(stream, buf)
14 FILE *stream;
15 char *buf;
16 void
18 setbuffer(stream, buf, size)
19 FILE *stream;
20 char *buf;
21 size_t size;
22 int
24 setlinebuf(stream)
25 FILE *stream;
26 int
28 setvbuf(stream, buf, mode, size)
29 FILE *stream;
30 char *buf;
31 int mode;
32 size_t size
33
35 The three types of buffering available are unbuffered, block buffered,
36 and line buffered. When an output stream is unbuffered, information
37 appears on the destination file or terminal as soon as written; when it
38 is block buffered many characters are saved up and written as a block;
39 when it is line buffered characters are saved up until a newline is
40 output or input is read from any stream attached to a terminal device
41 (typically stdin). The function fflush(3) may be used to force the
42 block out early. (See fclose(3).)
43 Normally all files are block buffered. When the first I/O operation
45 occurs on a file, malloc(3) is called, and an optimally-sized buffer is
46 obtained. If a stream refers to a terminal (as stdout normally does)
47 it is line buffered. The standard error stream stderr is always
48 unbuffered.
49 The setvbuf function may be used to alter the buffering behavior of a
51 stream. The mode parameter must be one of the following three macros:
52 _IONBF unbuffered
54 _IOLBF line buffered
56 _IOFBF fully buffered
58 The size parameter may be given as zero to obtain deferred optimal-size
60 buffer allocation as usual. If it is not zero, then except for
61 unbuffered files, the buf argument should point to a buffer at least
62 size bytes long; this buffer will be used instead of the current buf‐
63 fer. (If the size argument is not zero but buf is NULL, a buffer of
64 the given size will be allocated immediately, and released on close.
65 This is an extension to ANSI C; portable code should use a size of 0
66 with any NULL buffer.)
67 The setvbuf function may be used at any time, but may have peculiar
69 side effects (such as discarding input or flushing output) if the
70 stream is ``active''. Portable applications should call it only once
71 on any given stream, and before any I/O is performed.
72 The other three calls are, in effect, simply aliases for calls to
74 setvbuf. Except for the lack of a return value, the setbuf function is
75 exactly equivalent to the call
76 setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
78 The setbuffer function is the same, except that the size of the buffer
80 is up to the caller, rather than being determined by the default BUF‐
81 SIZ. The setlinebuf function is exactly equivalent to the call:
82 setvbuf(stream, (char *)NULL, _IOLBF, 0);
84
86 The setvbuf function returns 0 on success, or EOF if the request cannot
87 be honored (note that the stream is still functional in this case).
88 The setlinebuf function returns what the equivalent setvbuf would have
90 returned.
91
93 fopen(3), fclose(3), fread(3), malloc(3), puts(3), printf(3)
94
96 The setbuf and setvbuf functions conform to ANSI C X3.159-1989 (``ANSI
97 C'').
98
100 The setbuffer and setlinebuf functions are not portable to versions of
101 BSD before 4.2BSD. On 2BSD systems, setbuf always uses a 1kb buffer
102 size.
1034th Berkeley Distribution July 28, 1997 SETBUF(3)