| [9] | 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.3s 6.2 (Berkeley) 5/12/86
|
|---|
| 6 | .\"
|
|---|
| 7 | .TH SETBUF 3 "May 12, 1986"
|
|---|
| 8 | .UC 4
|
|---|
| 9 | .SH NAME
|
|---|
| 10 | setbuf, setvbuf \- assign buffering to a stream
|
|---|
| 11 | .SH SYNOPSIS
|
|---|
| 12 | .nf
|
|---|
| 13 | .ft B
|
|---|
| 14 | #include <stdio.h>
|
|---|
| 15 |
|
|---|
| 16 | int setbuf(FILE *\fIstream\fP, char *\fIbuf\fP)
|
|---|
| 17 | int setvbuf(FILE *\fIstream\fP, char *\fIbuf\fP, int \fItype\fP, size_t \fIsize\fP)
|
|---|
| 18 | .SH DESCRIPTION
|
|---|
| 19 | The three types of buffering available are unbuffered, block buffered,
|
|---|
| 20 | and line buffered.
|
|---|
| 21 | When an output stream is unbuffered, information appears on the
|
|---|
| 22 | destination file or terminal as soon as written;
|
|---|
| 23 | when it is block buffered many characters are saved up and written as a block;
|
|---|
| 24 | when it is line buffered characters are saved up until a newline is
|
|---|
| 25 | encountered or input is read from stdin.
|
|---|
| 26 | .B Fflush
|
|---|
| 27 | (see
|
|---|
| 28 | .BR fclose (3))
|
|---|
| 29 | may be used to force the block out early.
|
|---|
| 30 | Normally all files are block buffered.
|
|---|
| 31 | A buffer is obtained from
|
|---|
| 32 | .BR malloc (3)
|
|---|
| 33 | upon the first
|
|---|
| 34 | .B getc
|
|---|
| 35 | or
|
|---|
| 36 | .BR putc (3)
|
|---|
| 37 | on the file.
|
|---|
| 38 | If the standard stream
|
|---|
| 39 | .B stdout
|
|---|
| 40 | refers to a terminal it is line buffered.
|
|---|
| 41 | The standard stream
|
|---|
| 42 | .B stderr
|
|---|
| 43 | is always unbuffered.
|
|---|
| 44 | .PP
|
|---|
| 45 | .B Setbuf
|
|---|
| 46 | is used after a stream has been opened but before it is read or written.
|
|---|
| 47 | The character array
|
|---|
| 48 | .I buf
|
|---|
| 49 | is used instead of an automatically allocated buffer. If
|
|---|
| 50 | .I buf
|
|---|
| 51 | is the constant pointer
|
|---|
| 52 | .SM
|
|---|
| 53 | .BR NULL ,
|
|---|
| 54 | input/output will be completely unbuffered.
|
|---|
| 55 | A manifest constant
|
|---|
| 56 | .SM
|
|---|
| 57 | .B BUFSIZ
|
|---|
| 58 | tells how big an array is needed:
|
|---|
| 59 | .IP
|
|---|
| 60 | .B char
|
|---|
| 61 | buf[BUFSIZ];
|
|---|
| 62 | .PP
|
|---|
| 63 | .BR Setvbuf ,
|
|---|
| 64 | an alternate form of
|
|---|
| 65 | .BR setbuf ,
|
|---|
| 66 | is used after a stream has been opened but before it is read or written.
|
|---|
| 67 | It has three uses, depending on the value of the
|
|---|
| 68 | .IR type
|
|---|
| 69 | argument:
|
|---|
| 70 | .TP 5
|
|---|
| 71 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOFBF, \fIsize\fP)"
|
|---|
| 72 | Causes input/output to be fully buffered using the character array
|
|---|
| 73 | .I buf
|
|---|
| 74 | whose size is determined by the
|
|---|
| 75 | .I size
|
|---|
| 76 | argument.
|
|---|
| 77 | If
|
|---|
| 78 | .I buf
|
|---|
| 79 | is the constant pointer
|
|---|
| 80 | .SM
|
|---|
| 81 | .BR NULL ,
|
|---|
| 82 | then an automatically allocated buffer will be used.
|
|---|
| 83 | .TP 5
|
|---|
| 84 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOLBF, \fIsize\fP)"
|
|---|
| 85 | Like above, except that output will be line buffered, i.e. the buffer will
|
|---|
| 86 | be flushed when a newline is written, the buffer is full, or input is
|
|---|
| 87 | requested.
|
|---|
| 88 | .TP 5
|
|---|
| 89 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IONBF, \fIsize\fP)"
|
|---|
| 90 | Causes input/output to be completely unbuffered.
|
|---|
| 91 | .I Buf
|
|---|
| 92 | and
|
|---|
| 93 | .I size
|
|---|
| 94 | are ignored.
|
|---|
| 95 | .PP
|
|---|
| 96 | A file can be changed between unbuffered, line buffered, or block buffered
|
|---|
| 97 | by using
|
|---|
| 98 | .B freopen
|
|---|
| 99 | (see
|
|---|
| 100 | .BR fopen (3))
|
|---|
| 101 | followed by the appropriate
|
|---|
| 102 | .B setvbuf
|
|---|
| 103 | call.
|
|---|
| 104 | .SH "SEE ALSO"
|
|---|
| 105 | .BR fopen (3),
|
|---|
| 106 | .BR getc (3),
|
|---|
| 107 | .BR putc (3),
|
|---|
| 108 | .BR malloc (3),
|
|---|
| 109 | .BR fclose (3),
|
|---|
| 110 | .BR puts (3),
|
|---|
| 111 | .BR printf (3),
|
|---|
| 112 | .BR fread (3).
|
|---|
