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.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH LSEEK64 3 2004-12-11 "Linux" "Linux Programmer's Manual"
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.SH NAME
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lseek64 \- reposition 64-bit read/write file offset
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.SH SYNOPSIS
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.B #define _LARGEFILE64_SOURCE
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.br
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.B #include <sys/types.h>
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.br
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.B #include <unistd.h>
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.sp
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.BI "off64_t lseek64(int " fd ", off64_t " offset ", int " whence );
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.SH DESCRIPTION
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The
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.BR lseek (2)
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family functions reposition the offset of the file descriptor
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.I fd
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to
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.I offset
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bytes relative to start, current position, or end-of-file of the file,
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when
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.I whence
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has the value
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.BR SEEK_SET ,
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.BR SEEK_CUR ,
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or
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.BR SEEK_END ,
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respectively.
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.LP
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For more details, return value, and errors, see
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.BR lseek (2).
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.PP
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Four interfaces are available:
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.IR lseek() ,
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.IR lseek64() ,
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.IR llseek() ,
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and the raw system call
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.IR _llseek() .
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.SS lseek
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Prototype:
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.nf
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.sp
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.in +5n
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.BI "off_t lseek(int " fd ", off_t " offset ", int " whence );
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.in -5n
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.fi
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.sp
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The library routine
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.I lseek()
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uses the type
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.B off_t
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which is a 32-bit signed type on 32-bit architectures, unless one
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compiles with
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.nf
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.sp
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.in +5n
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#define _FILE_OFFSET_BITS 64
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.in -5n
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.sp
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.fi
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in which case it is a 64-bit signed type.
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.SS lseek64
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Prototype:
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.nf
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.sp
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.in +5n
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.BI "off64_t lseek64(int " fd ", off64_t " offset ", int " whence );
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.in -5n
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.fi
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.sp
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The library routine
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.I lseek64()
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uses a 64-bit type even when
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.B off_t
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is a 32-bit type. Its prototype (and the type
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.BR off64_t )
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is available only when one compiles with
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.nf
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.sp
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.in +5n
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#define _LARGEFILE64_SOURCE
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.in -5n
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.sp
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.fi
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The function
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.I lseek64()
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.\" in glibc 2.0.94, not in 2.0.6
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is available since glibc 2.1, and is defined to be an alias of
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.IR llseek() .
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.SS llseek
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Prototype:
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.nf
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.sp
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.in +5n
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.BI "loff_t llseek(int " fd ", loff_t " offset ", int " whence );
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.in -5n
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.fi
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.sp
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The type
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.B loff_t
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is a 64-bit signed type.
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The library routine
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.I llseek()
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.\" in libc 5.0.9, not in 4.7.6
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is available in libc5 and glibc and works without special defines.
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Its prototype was given in
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.I <unistd.h>
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with libc5, but glibc does not provide a prototype.
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This is bad, since a prototype is needed. Users should add
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the above prototype, or something equivalent, to their own source.
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When users complained about data loss caused by a miscompilation of
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.BR e2fsck (8),
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glibc 2.1.3 added the link-time warning
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.sp
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.in +5n
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"the `llseek' function may be dangerous; use `lseek64' instead."
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.in -5b
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.sp
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This makes this function unusable if one desires a warning-free
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compilation.
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.SS _llseek
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All the above functions are implemented in terms of the system call.
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The prototype is:
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.nf
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.sp
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.in +5n
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.BI "int _llseek (int " fd ", off_t " offset_hi ", off_t " offset_lo ,
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.BI "loff_t *" result ", int " whence );
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.in -5n
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.fi
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.sp
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For more details, see
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.BR llseek (2).
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.SH "SEE ALSO"
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.BR llseek (2),
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.BR lseek (2)
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