100 lines
2.3 KiB
Groff
100 lines
2.3 KiB
Groff
.\" Copyright (c) 1980 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)fopen.3s 6.3 (Berkeley) 5/27/86
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.\"
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.TH FOPEN 3 "May 27, 1986"
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.UC 4
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.SH NAME
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fopen, freopen, fdopen \- open a stream
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.SH SYNOPSIS
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.nf
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.ft B
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#include <stdio.h>
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FILE *fopen(const char *\fIfilename\fP, const char *\fItype\fP)
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FILE *freopen(const char *\fIfilename\fP, const char *\fItype\fP, FILE *\fIstream\fP)
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FILE *fdopen(int \fIfildes\fP, const char *\fItype\fP)
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.ft R
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.fi
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.SH DESCRIPTION
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.B Fopen
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opens the file named by
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.I filename
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and associates a stream with it.
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.B Fopen
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returns a pointer to be used to identify the stream in subsequent operations.
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.PP
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.I Type
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is a character string having one of the following values:
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.TP 5
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"r"
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open for reading
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.ns
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.TP 5
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"w"
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create for writing
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.ns
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.TP 5
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"a"
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append: open for writing at end of file, or create for writing
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.PP
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In addition, each
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.I type
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may be followed by a "+" to have the file opened for reading and writing.
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"r+" positions the stream at the beginning of the file, "w+" creates
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or truncates it, and "a+" positions it at the end. Both reads and writes
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may be used on read/write streams, with the limitation that an
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.BR fseek ,
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.BR rewind ,
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or reading an end-of-file must be used between a read and a write or vice-versa.
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.PP
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.B Freopen
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substitutes the named file in place of the open
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.IR stream .
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It returns the original value of
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.IR stream .
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The original stream is closed.
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.PP
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.B Freopen
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is typically used to attach the preopened constant names,
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.B stdin, stdout, stderr,
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to specified files.
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.PP
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.B Fdopen
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associates a stream with a file descriptor obtained from
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.BR open ,
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.BR dup ,
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.BR creat ,
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or
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.BR pipe (2).
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The
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.I type
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of the stream must agree with the mode of the open file.
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.SH "SEE ALSO"
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.BR open (2),
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.BR fclose (3).
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.SH DIAGNOSTICS
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.B Fopen
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and
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.B freopen
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return the pointer
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.SM
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.B NULL
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if
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.I filename
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cannot be accessed,
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if too many files are already open,
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or if other resources needed cannot be allocated.
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.SH BUGS
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.B Fdopen
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is not portable to systems other than UNIX.
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.PP
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The read/write
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.I types
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do not exist on all systems. Those systems without
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read/write modes will probably treat the
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.I type
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as if the "+" was not present. These are unreliable in any event.
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