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140 lines
3.9 KiB
Groff
140 lines
3.9 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)lseek.2 8.3 (Berkeley) 4/19/94
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.\"
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.TH LSEEK 2 "22 January 1997" GNO "System Calls"
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.SH NAME
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.BR lseek
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\- reposition read/write file offset
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.SH SYNOPSIS
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.br
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#include <unistd.h>
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.sp 1
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off_t
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\fBlseek\fR (int \fIfildes\fR, off_t \fIoffset\fR, int \fIwhence\fR);
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.SH DESCRIPTION
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The
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.BR lseek
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function repositions the offset of the file descriptor
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.I fildes
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to the
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argument
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.I offset
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according to the directive
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.I whence.
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The argument
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.I fildes
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must be an open
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file descriptor.
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.BR Lseek
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repositions the file pointer
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.I fildes
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as follows:
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.RS
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.It
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If
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.I whence
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is
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.BR SEEK_SET ,
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the offset is set to
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.I offset
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bytes.
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.It
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If
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.I whence
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is
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.BR SEEK_CUR ,
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the offset is set to its current location plus
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.I offset
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bytes.
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.It
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If
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.I whence
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is
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.BR SEEK_END ,
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the offset is set to the size of the
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file plus
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.I offset
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bytes.
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.RE
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.LP
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The
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.BR lseek
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function allows the file offset to be set beyond the end
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of the existing end-of-file of the file. If data is later written
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at this point, subsequent reads of the data in the gap return
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bytes of zeros (until data is actually written into the gap).
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.LP
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Some devices are incapable of seeking. The value of the pointer
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associated with such a device is undefined.
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.SH RETURN VALUES
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Upon successful completion,
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.BR lseek
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returns the resulting offset location as measured in bytes from the
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beginning of the file.
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Otherwise,
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a value of -1 is returned and
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.IR errno
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is set to indicate
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the error.
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.SH ERRORS
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.BR Lseek
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will fail and the file pointer will remain unchanged if:
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.RS
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.IP \fBEBADF\fR
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.IR Fildes
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is not an open file descriptor.
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.IP \fBESPIPE\fR
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.IR Fildes
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is associated with a pipe, socket, or FIFO.
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.IP \fBEINVAL\fR
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.I Whence
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is not a proper value.
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.RE
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.SH SEE ALSO
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.BR dup (2),
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.BR open (2)
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.SH BUGS
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In the GNO implementation, doing an
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.BR lseek
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past the end of file is permitted, but the created gap (as mentioned
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above) is not gauranteed to contain bytes of zeros.
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.LP
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This document's use of
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.I whence
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is incorrect English, but is maintained for historical reasons.
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.SH STANDARDS
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The
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.BR lseek
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function
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conforms to IEEE Std 1003.1-1988 (POSIX).
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