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<title>Error Reporting - GNU Scientific Library -- Reference Manual</title>
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<h3 class="section">3.1 Error Reporting</h3>
<p>The library follows the thread-safe error reporting conventions of the
<span class="sc">posix</span> Threads library. Functions return a non-zero error code to
indicate an error and <code>0</code> to indicate success.
<pre class="example"> int status = gsl_function (...)
if (status) { /* an error occurred */
.....
/* status value specifies the type of error */
}
</pre>
<p>The routines report an error whenever they cannot perform the task
requested of them. For example, a root-finding function would return a
non-zero error code if could not converge to the requested accuracy, or
exceeded a limit on the number of iterations. Situations like this are
a normal occurrence when using any mathematical library and you should
check the return status of the functions that you call.
<p>Whenever a routine reports an error the return value specifies the type
of error. The return value is analogous to the value of the variable
<code>errno</code> in the C library. The caller can examine the return code
and decide what action to take, including ignoring the error if it is
not considered serious.
<p>In addition to reporting errors by return codes the library also has an
error handler function <code>gsl_error</code>. This function is called by
other library functions when they report an error, just before they
return to the caller. The default behavior of the error handler is to
print a message and abort the program,
<pre class="example"> gsl: file.c:67: ERROR: invalid argument supplied by user
Default GSL error handler invoked.
Aborted
</pre>
<p>The purpose of the <code>gsl_error</code> handler is to provide a function
where a breakpoint can be set that will catch library errors when
running under the debugger. It is not intended for use in production
programs, which should handle any errors using the return codes.
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