116 lines
3.8 KiB
HTML
116 lines
3.8 KiB
HTML
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Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009, 2013
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The President and Fellows of Harvard College.
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Redistribution and use in source and binary forms, with or without
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THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
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OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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-->
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<html>
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<head>
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<title>read</title>
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<link rel="stylesheet" type="text/css" media="all" href="../man.css">
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</head>
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<body bgcolor=#ffffff>
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<h2 align=center>read</h2>
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<h4 align=center>OS/161 Reference Manual</h4>
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<h3>Name</h3>
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<p>
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read - read data from file
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</p>
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<h3>Library</h3>
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<p>
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Standard C Library (libc, -lc)
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</p>
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<h3>Synopsis</h3>
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<p>
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<tt>#include <unistd.h></tt><br>
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<br>
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<tt>ssize_t</tt><br>
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<tt>read(int </tt><em>fd</em><tt>, void *</tt><em>buf</em><tt>,
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size_t </tt><em>buflen</em><tt>);</tt>
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</p>
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<h3>Description</h3>
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<p>
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<tt>read</tt> reads up to <em>buflen</em> bytes from the file
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specified by <em>fd</em>, at the location in the file specified by the
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current seek position of the file, and stores them in the space
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pointed to by <em>buf</em>. The file must be open for reading.
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</p>
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<p>
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The current seek position of the file is advanced by the number of
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bytes read.
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</p>
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<p>
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Each read (or <A HREF=write.html>write</A>) operation is atomic
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relative to other I/O to the same file.
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Note that the kernel is not obliged to (and generally cannot) make the
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read atomic with respect to other threads in the same process
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accessing the I/O buffer during the read.
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</p>
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<h3>Return Values</h3>
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<p>
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The count of bytes read is returned. This count should be
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positive. A return value of 0 should be construed as signifying
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end-of-file. On error, <tt>read</tt> returns -1 and sets
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<A HREF=errno.html>errno</A> to a suitable error code for the error
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condition encountered.
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</p>
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<p>
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Note that in some cases, particularly on devices, fewer than
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<em>buflen</em> (but greater than zero) bytes may be returned. This
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depends on circumstances and does not necessarily signify
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end-of-file.
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</p>
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<h3>Errors</h3>
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<p>
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The following error codes should be returned under the conditions
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given. Other error codes may be returned for other cases not
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mentioned here.
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<table width=90%>
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<tr><td width=5% rowspan=3> </td>
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<td width=10% valign=top>EBADF</td>
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<td><em>fd</em> is not a valid file descriptor, or was
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not opened for reading.</td></tr>
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<tr><td valign=top>EFAULT</td>
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<td>Part or all of the address space pointed to by
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<em>buf</em> is invalid.</td></tr>
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<tr><td valign=top>EIO</td>
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<td>A hardware I/O error occurred reading the
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data.</td></tr>
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</table>
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</p>
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</body>
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</html>
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