273 lines
5.4 KiB
HTML
273 lines
5.4 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of LSEEK64</TITLE>
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</HEAD><BODY>
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<H1>LSEEK64</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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lseek64 - reposition 64-bit read/write file offset
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#define _LARGEFILE64_SOURCE</B> /* See <A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A>(7) */
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<BR>
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<B>#include <<A HREF="file:///usr/include/sys/types.h">sys/types.h</A>></B>
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<BR>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<P>
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<B>off64_t lseek64(int </B><I>fd</I><B>, off64_t </B><I>offset</I><B>, int </B><I>whence</I><B>);</B>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2)
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family of functions reposition the offset of the open file associated
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with the file descriptor
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<I>fd</I>
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to
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<I>offset</I>
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bytes relative to the start, current position, or end of the file,
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when
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<I>whence</I>
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has the value
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<B>SEEK_SET</B>,
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<B>SEEK_CUR</B>,
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or
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<B>SEEK_END</B>,
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respectively.
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<P>
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For more details, return value, and errors, see
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2).
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<P>
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Four interfaces are available:
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2),
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<B>lseek64</B>(),
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<B><A HREF="/cgi-bin/man/man2html?2+llseek">llseek</A></B>(2),
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and
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<B><A HREF="/cgi-bin/man/man2html?2+_llseek">_llseek</A></B>(2).
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<A NAME="lbAE"> </A>
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<H3>lseek()</H3>
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Prototype:
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<P>
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<B>off_t lseek(int </B><I>fd</I><B>, off_t </B><I>offset</I><B>, int </B><I>whence</I><B>);</B>
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<P>
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2)
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uses the type
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<I>off_t</I>.
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This is a 32-bit signed type on 32-bit architectures, unless one
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compiles with
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<P>
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#define _FILE_OFFSET_BITS 64
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<P>
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in which case it is a 64-bit signed type.
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<A NAME="lbAF"> </A>
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<H3>lseek64()</H3>
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Prototype:
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<P>
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<B>off64_t lseek64(int </B><I>fd</I><B>, off64_t </B><I>offset</I><B>, int </B><I>whence</I><B>);</B>
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<P>
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The library routine
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<B>lseek64</B>()
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uses a 64-bit type even when
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<I>off_t</I>
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is a 32-bit type.
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Its prototype (and the type
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<I>off64_t</I>)
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is available only when one compiles with
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<P>
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#define _LARGEFILE64_SOURCE
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<P>
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The function
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<B>lseek64</B>()
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is available since glibc 2.1, and is defined to be an alias for
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<B>llseek</B>().
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<A NAME="lbAG"> </A>
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<H3>llseek()</H3>
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Prototype:
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<P>
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<B>loff_t llseek(int </B><I>fd</I><B>, loff_t </B><I>offset</I><B>, int </B><I>whence</I><B>);</B>
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<P>
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The type
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<I>loff_t</I>
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is a 64-bit signed type.
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The library routine
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<B>llseek</B>()
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is available in glibc and works without special defines.
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However, the glibc headers do not provide a prototype.
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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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<B><A HREF="/cgi-bin/man/man2html?8+e2fsck">e2fsck</A></B>(8),
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glibc 2.1.3 added the link-time warning
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<P>
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"the `llseek' function may be dangerous; use `lseek64' instead."
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<P>
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This makes this function unusable if one desires a warning-free
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compilation.
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<A NAME="lbAH"> </A>
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<H3>_llseek()</H3>
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On 32-bit architectures,
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this is the system call that is used to implement all of the above functions.
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The prototype is:
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<P>
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<B>int _llseek(int </B><I>fd</I><B>, off_t </B><I>offset_hi</I><B>, off_t </B><I>offset_lo</I><B>,</B>
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<B> loff_t *</B><I>result</I><B>, int </B><I>whence</I><B>);</B>
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<P>
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For more details, see
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<B><A HREF="/cgi-bin/man/man2html?2+llseek">llseek</A></B>(2).
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<P>
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64-bit systems don't need an
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<B>_llseek</B>()
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system call.
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Instead, they have an
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2)
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system call that supports 64-bit file offsets.
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<A NAME="lbAI"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>lseek64</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+llseek">llseek</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+lseek">lseek</A></B>(2)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DL>
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<DT id="4"><A HREF="#lbAE">lseek()</A><DD>
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<DT id="5"><A HREF="#lbAF">lseek64()</A><DD>
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<DT id="6"><A HREF="#lbAG">llseek()</A><DD>
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<DT id="7"><A HREF="#lbAH">_llseek()</A><DD>
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</DL>
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<DT id="8"><A HREF="#lbAI">ATTRIBUTES</A><DD>
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<DT id="9"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="10"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:47 GMT, March 31, 2021
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