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Rev Author # Line
1 perry 1 SETBUF
2 !!!SETBUF
3 NAME
4 SYNOPSIS
5 DESCRIPTION
6 RETURN VALUE
7 CONFORMING TO
8 BUGS
9 SEE ALSO
10 ----
11 !!NAME
12
13
14 setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations
15 !!SYNOPSIS
16
17
18 __#include __
19
20
21 __void setbuf(FILE *__''stream''__, char
22 *__''buf''__);
23 void setbuffer(FILE *__''stream''__, char
24 *__''buf''__, size_t__''size''__);
25 void setlinebuf(FILE *__''stream''__);
26 int setvbuf(FILE *__''stream''__, char
27 *__''buf''__, int__ ''mode'' __, size_t__
28 ''size''__);__
29 !!DESCRIPTION
30
31
32 The three types of buffering available are unbuffered, block
33 buffered, and line buffered. When an output stream is
34 unbuffered, information appears on the destination file or
35 terminal as soon as written; when it is block buffered many
36 characters are saved up and written as a block; when it is
37 line buffered characters are saved up until a newline is
38 output or input is read from any stream attached to a
39 terminal device (typically stdin). The function
40 fflush(3) may be used to force the block out early.
41 (See fclose(3).) Normally all files are block
42 buffered. When the first I/O operation occurs on a file,
43 malloc(3) is called, and a buffer is obtained. If a
44 stream refers to a terminal (as ''stdout'' normally does)
45 it is line buffered. The standard error stream ''stderr''
46 is always unbuffered by default.
47
48
49 The __setvbuf__ function may be used on any open stream
50 to change its buffer. The ''mode'' parameter must be one
51 of the following three macros:
52
53
54 ___IONBF__
55
56
57 unbuffered
58
59
60 ___IOLBF__
61
62
63 line buffered
64
65
66 ___IOFBF__
67
68
69 fully buffered
70
71
72 Except for unbuffered files, the ''buf'' argument should
73 point to a buffer at least ''size'' bytes long; this
74 buffer will be used instead of the current buffer. If the
75 argument ''buf'' is __NULL__, only the mode is
76 affected; a new buffer will be allocated on the next read or
77 write operation. The ''setvbuf'' function may only be
78 used after opening a stream and before any other operations
79 have been performed on it.
80
81
82 The other three calls are, in effect, simply aliases for
83 calls to __setvbuf__. The __setbuf__ function is
84 exactly equivalent to the call
85
86
87 setvbuf(stream, buf, buf ? _IOFBF : _IONBF,
88 BUFSIZ);
89
90
91 The __setbuffer__ function is the same, except that the
92 size of the buffer is up to the caller, rather than being
93 determined by the default __BUFSIZ__. The
94 __setlinebuf__ function is exactly equivalent to the
95 call:
96
97
98 setvbuf(stream, (char *)NULL, _IOLBF, 0);
99 !!RETURN VALUE
100
101
102 The function __setvbuf__ returns 0 on success. It can
103 return any value on failure, but returns nonzero when
104 ''mode'' is invalid or the request cannot be honoured. It
105 may set ''errno'' on failure. The other functions are
106 void.
107 !!CONFORMING TO
108
109
110 The __setbuf__ and __setvbuf__ functions conform to
111 ANSI X3.159-1989 (``ANSI C'').
112 !!BUGS
113
114
115 The __setbuffer__ and __setlinebuf__ functions are not
116 portable to versions of BSD before 4.2BSD, and are available
117 under Linux since libc 4.5.21. On 4.2BSD and 4.3BSD systems,
118 __setbuf__ always uses a suboptimal buffer size and
119 should be avoided.
120
121
122 You must make sure that both ''buf'' and the space it
123 points to still exist by the time ''stream'' is closed,
124 which also happens at program termination.
125
126
127 For example, the following is illegal:
128
129
130 #include
131 !!SEE ALSO
132
133
134 fclose(3), fflush(3), fopen(3),
135 fread(3), malloc(3), printf(3),
136 puts(3)
137 ----
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