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1.1 root 1: .\" Copyright (c) 1980 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)setbuf.3 6.3 (Berkeley) 10/16/87
6: .\"
7: .TH SETBUF 3S "October 16, 1987"
8: .UC 4
9: .SH NAME
10: setbuf, setbuffer, setlinebuf \- assign buffering to a stream
11: .SH SYNOPSIS
12: .B #include <stdio.h>
13: .PP
14: .B setbuf(stream, buf)
15: .br
16: .SM
17: .B FILE
18: .B *stream;
19: .br
20: .B char *buf;
21: .PP
22: .B setbuffer(stream, buf, size)
23: .br
24: .SM
25: .B FILE
26: .B *stream;
27: .br
28: .B char *buf;
29: .br
30: .B int size;
31: .PP
32: .B setlinebuf(stream)
33: .br
34: .SM
35: .B FILE
36: .B *stream;
37: .SH DESCRIPTION
38: The three types of buffering available are unbuffered, block buffered,
39: and line buffered.
40: When an output stream is unbuffered, information appears on the
41: destination file or terminal as soon as written;
42: when it is block buffered many characters are saved up and written as a block;
43: when it is line buffered characters are saved up until a newline is
44: encountered or input is read from stdin.
45: .I Fflush
46: (see
47: .IR fclose (3S))
48: may be used to force the block out early.
49: Normally all files are block buffered.
50: A buffer is obtained from
51: .IR malloc (3)
52: upon the first
53: .I getc
54: or
55: .IR putc (3S)
56: on the file.
57: If the standard stream
58: .B stdout
59: refers to a terminal it is line buffered.
60: The standard stream
61: .B stderr
62: is always unbuffered.
63: .PP
64: .I Setbuf
65: is used after a stream has been opened but before it is read or written.
66: The character array
67: .I buf
68: is used instead of an automatically allocated buffer. If
69: .I buf
70: is the constant pointer
71: .SM
72: .B NULL,
73: input/output will be completely unbuffered.
74: A manifest constant
75: .SM
76: .B BUFSIZ
77: tells how big an array is needed:
78: .IP
79: .B char
80: buf[BUFSIZ];
81: .PP
82: .IR Setbuffer ,
83: an alternate form of
84: .IR setbuf ,
85: is used after a stream has been opened but before it is read or written.
86: The character array
87: .I buf
88: whose size is determined by the
89: .I size
90: argument is used instead of an automatically allocated buffer. If
91: .I buf
92: is the constant pointer
93: .SM
94: .BR NULL ,
95: input/output will be completely unbuffered.
96: .PP
97: .I Setlinebuf
98: is used to change
99: .I stdout
100: or
101: .I stderr
102: from block buffered or unbuffered to line buffered.
103: Unlike
104: .I setbuf
105: and
106: .I setbuffer
107: it can be used at any time that the file descriptor is active.
108: .PP
109: A file can be changed from unbuffered or line buffered to block buffered
110: by using
111: .I freopen
112: (see
113: .IR fopen (3S)).
114: A file can be changed from block buffered or line buffered to unbuffered
115: by using
116: .I freopen
117: followed by
118: .I setbuf
119: with a buffer argument of
120: .SM
121: .BR NULL .
122: .SH "SEE ALSO"
123: fopen(3S),
124: getc(3S),
125: putc(3S),
126: malloc(3),
127: fclose(3S),
128: puts(3S),
129: printf(3S),
130: fread(3S)
131: .SH BUGS
132: The
133: .I setbuffer
134: and
135: .I setlinebuf
136: functions are not portable to non-4.2BSD versions of UNIX.
137: On 4.2BSD and 4.3BSD systems,
138: .I setbuf
139: always uses a suboptimal buffer size and should be avoided.
140: .I Setbuffer
141: is not usually needed
142: as the default file I/O buffer sizes are optimal.
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