| 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 | .\" @(#)lseek.2 6.3 (Berkeley) 2/24/86
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| 6 | .\"
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| 7 | .TH LSEEK 2 "February 24, 1986"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | lseek \- move read/write pointer
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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 <sys/types.h>
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| 15 | #include <unistd.h>
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| 16 |
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| 17 | .ta +1.8i +0.6i
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| 18 | #define SEEK_SET 0 /* offset is absolute */
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| 19 | #define SEEK_CUR 1 /* relative to current position */
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| 20 | #define SEEK_END 2 /* relative to end of file */
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| 21 |
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| 22 | off_t lseek(int d, off_t offset, int whence)
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| 23 | .fi
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| 24 | .ft R
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| 25 | .SH DESCRIPTION
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| 26 | The descriptor
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| 27 | .I d
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| 28 | refers to a file or device open for reading and/or writing.
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| 29 | .B Lseek
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| 30 | sets the file pointer of
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| 31 | .I d
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| 32 | as follows:
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| 33 | .IP
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| 34 | If
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| 35 | .I whence
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| 36 | is SEEK_SET, the pointer is set to
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| 37 | .I offset
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| 38 | bytes.
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| 39 | .IP
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| 40 | If
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| 41 | .I whence
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| 42 | is SEEK_CUR, the pointer is set to its current location plus
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| 43 | .IR offset .
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| 44 | .IP
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| 45 | If
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| 46 | .I whence
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| 47 | is SEEK_END, the pointer is set to the size of the
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| 48 | file plus
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| 49 | .IR offset .
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| 50 | .PP
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| 51 | Upon successful completion, the resulting pointer location
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| 52 | as measured in bytes from beginning of the file is returned.
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| 53 | Some devices are incapable of seeking. The value of the pointer
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| 54 | associated with such a device is undefined.
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| 55 | .SH NOTES
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| 56 | Seeking far beyond the end of a file, then writing,
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| 57 | creates a gap or \*(lqhole\*(rq, which occupies no
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| 58 | physical space and reads as zeros.
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| 59 | .SH "RETURN VALUE
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| 60 | Upon successful completion,
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| 61 | the current file pointer value is returned.
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| 62 | Otherwise,
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| 63 | a value of \-1 is returned and \fBerrno\fP is set to indicate
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| 64 | the error.
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| 65 | .SH "ERRORS
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| 66 | .B Lseek
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| 67 | will fail and the file pointer will remain unchanged if:
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| 68 | .TP 15
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| 69 | [EBADF]
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| 70 | .I Fildes
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| 71 | is not an open file descriptor.
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| 72 | .TP 15
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| 73 | [ESPIPE]
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| 74 | .I Fildes
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| 75 | is associated with a pipe or a socket.
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| 76 | .TP 15
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| 77 | [EINVAL]
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| 78 | .I Whence
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| 79 | is not a proper value.
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| 80 | .SH "SEE ALSO"
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| 81 | .BR fcntl (2),
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| 82 | .BR open (2).
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| 83 | .SH BUGS
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| 84 | This document's use of
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| 85 | .I whence
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| 86 | is incorrect English, but maintained for historical reasons.
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