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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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| </font></tt> |
| <tt><font size=+1>long write(int fd, void *buf, long nbytes) |
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| </font></tt> |
| <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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| </table> |
| <p><font size=+1><b>DIAGNOSTICS </b></font><br> |
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| These functions set <i>errstr</i>.<br> |
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