| 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 | .\" @(#)fopen.3s 6.3 (Berkeley) 5/27/86
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| 6 | .\"
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| 7 | .TH FOPEN 3 "May 27, 1986"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | fopen, freopen, fdopen \- open 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 | FILE *fopen(const char *\fIfilename\fP, const char *\fItype\fP)
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| 17 | FILE *freopen(const char *\fIfilename\fP, const char *\fItype\fP, FILE *\fIstream\fP)
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| 18 | FILE *fdopen(int \fIfildes\fP, const char *\fItype\fP)
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| 19 | .ft R
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| 20 | .fi
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| 21 | .SH DESCRIPTION
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| 22 | .B Fopen
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| 23 | opens the file named by
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| 24 | .I filename
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| 25 | and associates a stream with it.
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| 26 | .B Fopen
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| 27 | returns a pointer to be used to identify the stream in subsequent operations.
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| 28 | .PP
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| 29 | .I Type
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| 30 | is a character string having one of the following values:
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| 31 | .TP 5
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| 32 | "r"
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| 33 | open for reading
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| 34 | .ns
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| 35 | .TP 5
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| 36 | "w"
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| 37 | create for writing
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| 38 | .ns
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| 39 | .TP 5
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| 40 | "a"
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| 41 | append: open for writing at end of file, or create for writing
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| 42 | .PP
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| 43 | In addition, each
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| 44 | .I type
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| 45 | may be followed by a "+" to have the file opened for reading and writing.
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| 46 | "r+" positions the stream at the beginning of the file, "w+" creates
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| 47 | or truncates it, and "a+" positions it at the end. Both reads and writes
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| 48 | may be used on read/write streams, with the limitation that an
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| 49 | .BR fseek ,
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| 50 | .BR rewind ,
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| 51 | or reading an end-of-file must be used between a read and a write or vice-versa.
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| 52 | .PP
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| 53 | .B Freopen
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| 54 | substitutes the named file in place of the open
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| 55 | .IR stream .
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| 56 | It returns the original value of
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| 57 | .IR stream .
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| 58 | The original stream is closed.
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| 59 | .PP
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| 60 | .B Freopen
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| 61 | is typically used to attach the preopened constant names,
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| 62 | .B stdin, stdout, stderr,
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| 63 | to specified files.
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| 64 | .PP
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| 65 | .B Fdopen
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| 66 | associates a stream with a file descriptor obtained from
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| 67 | .BR open ,
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| 68 | .BR dup ,
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| 69 | .BR creat ,
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| 70 | or
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| 71 | .BR pipe (2).
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| 72 | The
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| 73 | .I type
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| 74 | of the stream must agree with the mode of the open file.
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| 75 | .SH "SEE ALSO"
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| 76 | .BR open (2),
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| 77 | .BR fclose (3).
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| 78 | .SH DIAGNOSTICS
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| 79 | .B Fopen
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| 80 | and
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| 81 | .B freopen
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| 82 | return the pointer
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| 83 | .SM
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| 84 | .B NULL
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| 85 | if
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| 86 | .I filename
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| 87 | cannot be accessed,
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| 88 | if too many files are already open,
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| 89 | or if other resources needed cannot be allocated.
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| 90 | .SH BUGS
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| 91 | .B Fdopen
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| 92 | is not portable to systems other than UNIX.
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| 93 | .PP
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| 94 | The read/write
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| 95 | .I types
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| 96 | do not exist on all systems. Those systems without
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| 97 | read/write modes will probably treat the
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| 98 | .I type
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| 99 | as if the "+" was not present. These are unreliable in any event.
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