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<title>errstr(3) - Plan 9 from User Space</title>
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<tr><td width=20><td><b>ERRSTR(3)</b><td align=right><b>ERRSTR(3)</b>
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<p><font size=+1><b>NAME </b></font><br>
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errstr, rerrstr, werrstr – description of last system call error<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>int errstr(char *err, uint nerr)
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</font></tt>
<tt><font size=+1>void rerrstr(char *err, uint nerr)
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<tt><font size=+1>void werrstr(char *fmt, ...)<br>
</font></tt>
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<p><font size=+1><b>DESCRIPTION </b></font><br>
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When a system call fails it returns –1 and records a null terminated
string describing the error in a per-process buffer. <i>Errstr</i> swaps
the contents of that buffer with the contents of the array <i>err</i>.
<i>Errstr</i> will write at most <i>nerr</i> bytes into <i>err</i>; if the per-process
error string does not fit, it is silently truncated at a UTF
character boundary. The returned string is NUL-terminated. Usually
<i>errstr</i> will be called with an empty string, but the exchange property
provides a mechanism for libraries to set the return value for
the next call to <i>errstr</i>.
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The per-process buffer is <tt><font size=+1>ERRMAX</font></tt> bytes long. Any error string
provided by the user will be truncated at <tt><font size=+1>ERRMAX−1</font></tt> bytes. <tt><font size=+1>ERRMAX</font></tt>
is defined in <tt><font size=+1><libc.h></font></tt>.
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If no system call has generated an error since the last call to
<i>errstr</i> with an empty string, the result is an empty string.
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The verb <tt><font size=+1>r</font></tt> in <a href="../man3/print.html"><i>print</i>(3)</a> calls <i>errstr</i> and outputs the error string.
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<i>Rerrstr</i> reads the error string but does not modify the per-process
buffer, so a subsequent <i>errstr</i> will recover the same string.
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<i>Werrstr</i> takes a <i>print</i> style format as its argument and uses it
to format a string to pass to <i>errstr</i>. The string returned from
<i>errstr</i> is discarded.
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The error string is maintained in parallel with the Unix error
number <i>errno</i>. Changing <i>errno</i> will reset the error string, and
changing the error string via <i>errstr</i> or <i>werrstr</i> will reset <i>errno</i>.<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/errstr.c<br>
</font></tt>
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<p><font size=+1><b>DIAGNOSTICS </b></font><br>
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<i>Errstr</i> always returns 0.<br>
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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/perror.html"><i>perror</i>(3)</a><br>
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<p><font size=+1><b>BUGS </b></font><br>
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The implementation sets <i>errno</i> to the (somewhat arbitrary) constant
0x19283745 when the error string is valid. When <i>errno</i> is set to
other values, the error string is synthesized using <a href="../man3/strerror.html"><i>strerror</i>(3)</a>.<br>
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