| 1 | .\" Copyright (c) 1980 Regents of the University of California.
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| 2 | .\" All rights reserved. The Berkeley software License Agreement
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| 3 | .\" specifies the terms and conditions for redistribution.
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| 4 | .\"
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| 5 | .\" @(#)setbuf.3s 6.2 (Berkeley) 5/12/86
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| 6 | .\"
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| 7 | .TH SETBUF 3 "May 12, 1986"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | setbuf, setvbuf \- assign buffering to a stream
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| 11 | .SH SYNOPSIS
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| 12 | .nf
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| 13 | .ft B
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| 14 | #include <stdio.h>
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| 15 |
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| 16 | int setbuf(FILE *\fIstream\fP, char *\fIbuf\fP)
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| 17 | int setvbuf(FILE *\fIstream\fP, char *\fIbuf\fP, int \fItype\fP, size_t \fIsize\fP)
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| 18 | .SH DESCRIPTION
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| 19 | The three types of buffering available are unbuffered, block buffered,
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| 20 | and line buffered.
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| 21 | When an output stream is unbuffered, information appears on the
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| 22 | destination file or terminal as soon as written;
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| 23 | when it is block buffered many characters are saved up and written as a block;
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| 24 | when it is line buffered characters are saved up until a newline is
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| 25 | encountered or input is read from stdin.
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| 26 | .B Fflush
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| 27 | (see
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| 28 | .BR fclose (3))
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| 29 | may be used to force the block out early.
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| 30 | Normally all files are block buffered.
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| 31 | A buffer is obtained from
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| 32 | .BR malloc (3)
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| 33 | upon the first
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| 34 | .B getc
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| 35 | or
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| 36 | .BR putc (3)
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| 37 | on the file.
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| 38 | If the standard stream
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| 39 | .B stdout
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| 40 | refers to a terminal it is line buffered.
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| 41 | The standard stream
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| 42 | .B stderr
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| 43 | is always unbuffered.
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| 44 | .PP
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| 45 | .B Setbuf
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| 46 | is used after a stream has been opened but before it is read or written.
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| 47 | The character array
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| 48 | .I buf
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| 49 | is used instead of an automatically allocated buffer. If
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| 50 | .I buf
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| 51 | is the constant pointer
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| 52 | .SM
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| 53 | .BR NULL ,
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| 54 | input/output will be completely unbuffered.
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| 55 | A manifest constant
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| 56 | .SM
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| 57 | .B BUFSIZ
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| 58 | tells how big an array is needed:
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| 59 | .IP
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| 60 | .B char
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| 61 | buf[BUFSIZ];
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| 62 | .PP
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| 63 | .BR Setvbuf ,
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| 64 | an alternate form of
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| 65 | .BR setbuf ,
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| 66 | is used after a stream has been opened but before it is read or written.
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| 67 | It has three uses, depending on the value of the
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| 68 | .IR type
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| 69 | argument:
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| 70 | .TP 5
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| 71 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOFBF, \fIsize\fP)"
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| 72 | Causes input/output to be fully buffered using the character array
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| 73 | .I buf
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| 74 | whose size is determined by the
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| 75 | .I size
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| 76 | argument.
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| 77 | If
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| 78 | .I buf
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| 79 | is the constant pointer
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| 80 | .SM
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| 81 | .BR NULL ,
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| 82 | then an automatically allocated buffer will be used.
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| 83 | .TP 5
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| 84 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IOLBF, \fIsize\fP)"
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| 85 | Like above, except that output will be line buffered, i.e. the buffer will
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| 86 | be flushed when a newline is written, the buffer is full, or input is
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| 87 | requested.
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| 88 | .TP 5
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| 89 | .B "setvbuf(\fIstream\fP, \fIbuf\fP, _IONBF, \fIsize\fP)"
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| 90 | Causes input/output to be completely unbuffered.
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| 91 | .I Buf
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| 92 | and
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| 93 | .I size
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| 94 | are ignored.
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| 95 | .PP
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| 96 | A file can be changed between unbuffered, line buffered, or block buffered
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| 97 | by using
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| 98 | .B freopen
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| 99 | (see
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| 100 | .BR fopen (3))
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| 101 | followed by the appropriate
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| 102 | .B setvbuf
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| 103 | call.
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| 104 | .SH "SEE ALSO"
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| 105 | .BR fopen (3),
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| 106 | .BR getc (3),
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| 107 | .BR putc (3),
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| 108 | .BR malloc (3),
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| 109 | .BR fclose (3),
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| 110 | .BR puts (3),
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| 111 | .BR printf (3),
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| 112 | .BR fread (3).
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