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<title>read(3) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>READ(3)</b><td align=right><b>READ(3)</b>
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<p><font size=+1><b>NAME </b></font><br>
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read, readn, write, pread, pwrite – read or write file<br>
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<p><font size=+1><b>SYNOPSIS </b></font><br>
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<tt><font size=+1>#include <u.h><br>
#include <libc.h>
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<tt><font size=+1>long read(int fd, void *buf, long nbytes)
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</font></tt>
<tt><font size=+1>long readn(int fd, void *buf, long nbytes)
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<tt><font size=+1>long write(int fd, void *buf, long nbytes)
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<tt><font size=+1>long pread(int fd, void *buf, long nbytes, vlong offset)
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</font></tt>
<tt><font size=+1>long pwrite(int fd, void *buf, long nbytes, vlong offset)<br>
</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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<i>Read</i> reads <i>nbytes</i> bytes of data from the offset in the file associated
with <i>fd</i> into memory at <i>buf</i>. The offset is advanced by the number
of bytes read. It is not guaranteed that all <i>nbytes</i> bytes will
be read; for example if the file refers to the console, at most
one line will be returned. In any event the number of bytes
read is returned. A return value of 0 is conventionally interpreted
as end of file.
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<i>Readn</i> is just like read, but does successive <i>read</i> calls until
<i>nbytes</i> have been read, or a read system call returns a non-positive
count.
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<i>Write</i> writes <i>nbytes</i> bytes of data starting at <i>buf</i> to the file
associated with <i>fd</i> at the file offset. The offset is advanced
by the number of bytes written. The number of characters actually
written is returned. It should be regarded as an error if this
is not the same as requested.
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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
a <i>read</i> or <i>write</i>. By combining the operations in a single atomic
call, they more closely match the 9P protocol (see <i>intro</i>(9p))
and, more important, permit multiprocess programs to execute multiple
concurrent read and write operations on the same file
descriptor without interference.<br>
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<p><font size=+1><b>SOURCE </b></font><br>
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<tt><font size=+1>/usr/local/plan9/src/lib9/readn.c<br>
</font></tt>
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<p><font size=+1><b>SEE ALSO </b></font><br>
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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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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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These functions set <i>errstr</i>.<br>
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