110 lines
4.4 KiB
HTML
110 lines
4.4 KiB
HTML
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<head>
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<title>read(3) - Plan 9 from User Space</title>
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<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
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</head>
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<body bgcolor=#ffffff>
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<table border=0 cellpadding=0 cellspacing=0 width=100%>
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<tr height=10><td>
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<tr><td width=20><td>
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<tr><td width=20><td><b>READ(3)</b><td align=right><b>READ(3)</b>
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<tr><td width=20><td colspan=2>
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<br>
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<p><font size=+1><b>NAME </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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read, readn, write, pread, pwrite – read or write file<br>
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</table>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>#include <u.h><br>
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#include <libc.h>
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long read(int fd, void *buf, long nbytes)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long readn(int fd, void *buf, long nbytes)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long write(int fd, void *buf, long nbytes)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long pread(int fd, void *buf, long nbytes, vlong offset)
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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</font></tt>
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<tt><font size=+1>long pwrite(int fd, void *buf, long nbytes, vlong offset)<br>
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</font></tt>
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</table>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<i>Read</i> reads <i>nbytes</i> bytes of data from the offset in the file associated
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with <i>fd</i> into memory at <i>buf</i>. The offset is advanced by the number
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of bytes read. It is not guaranteed that all <i>nbytes</i> bytes will
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be read; for example if the file refers to the console, at most
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one line will be returned. In any event the number of bytes
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read is returned. A return value of 0 is conventionally interpreted
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as end of file.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Readn</i> is just like read, but does successive <i>read</i> calls until
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<i>nbytes</i> have been read, or a read system call returns a non-positive
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count.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Write</i> writes <i>nbytes</i> bytes of data starting at <i>buf</i> to the file
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associated with <i>fd</i> at the file offset. The offset is advanced
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by the number of bytes written. The number of characters actually
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written is returned. It should be regarded as an error if this
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is not the same as requested.
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<table border=0 cellpadding=0 cellspacing=0><tr height=5><td></table>
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<i>Pread</i> and <i>Pwrite</i> equivalent to a <a href="../man3/seek.html"><i>seek</i>(3)</a> to <i>offset</i> followed by
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a <i>read</i> or <i>write</i>. By combining the operations in a single atomic
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call, they more closely match the 9P protocol (see <i>intro</i>(9p))
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and, more important, permit multiprocess programs to execute multiple
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concurrent read and write operations on the same file
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descriptor without interference.<br>
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</table>
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<p><font size=+1><b>SOURCE </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<tt><font size=+1>/usr/local/plan9/src/lib9/readn.c<br>
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</font></tt>
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</table>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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<a href="../man3/intro.html"><i>intro</i>(3)</a>, <a href="../man3/open.html"><i>open</i>(3)</a>, <a href="../man3/dup.html"><i>dup</i>(3)</a>, <a href="../man3/pipe.html"><i>pipe</i>(3)</a><br>
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</table>
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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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<table border=0 cellpadding=0 cellspacing=0><tr height=2><td><tr><td width=20><td>
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These functions set <i>errstr</i>.<br>
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</table>
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<td width=20>
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<tr height=20><td>
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</table>
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<!-- TRAILER -->
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<table border=0 cellpadding=0 cellspacing=0 width=100%>
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<tr height=15><td width=10><td><td width=10>
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<tr><td><td>
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<center>
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<a href="../../"><img src="../../dist/spaceglenda100.png" alt="Space Glenda" border=1></a>
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</center>
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</table>
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<!-- TRAILER -->
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</body></html>
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