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<h2 class="chapter">2 Error Reporting</h2>

<!-- %MENU% How library functions report errors -->
<p><a name="index-error-reporting-54"></a><a name="index-reporting-errors-55"></a><a name="index-error-codes-56"></a><a name="index-status-codes-57"></a>
Many functions in the GNU C library detect and report error conditions,
and sometimes your programs need to check for these error conditions. 
For example, when you open an input file, you should verify that the
file was actually opened correctly, and print an error message or take
other appropriate action if the call to the library function failed.

   <p>This chapter describes how the error reporting facility works.  Your
program should include the header file <samp><span class="file">errno.h</span></samp> to use this
facility. 
<a name="index-errno_002eh-58"></a>

<ul class="menu">
<li><a accesskey="1" href="Checking-for-Errors.html#Checking-for-Errors">Checking for Errors</a>:          How errors are reported by library functions. 
<li><a accesskey="2" href="Error-Codes.html#Error-Codes">Error Codes</a>:                  Error code macros; all of these expand
                                 into integer constant values. 
<li><a accesskey="3" href="Error-Messages.html#Error-Messages">Error Messages</a>:               Mapping error codes onto error messages. 
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