devdocs/c/preprocessor%2Ferror.html


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    <h1 id="firstHeading" class="firstHeading">Diagnostic directives</h1>            <p>Shows the given error message and renders the program ill-formed<span class="t-rev-inl t-since-c23"><span>, or given warning message without affect the validity of the program</span><span><span class="t-mark-rev t-since-c23">(since C23)</span></span></span>.</p>
<h3 id="Syntax"> Syntax</h3> <table class="t-sdsc-begin">  <tr class="t-sdsc"> <td> <code>#error</code> <span class="t-spar">diagnostic-message</span> </td> <td> (1) </td> <td class="t-sdsc-nopad"> </td>
</tr>  <tr class="t-sdsc"> <td> <code>#warning</code> <span class="t-spar">diagnostic-message</span> </td> <td> (2) </td> <td> <span class="t-mark-rev t-since-c23">(since C23)</span> </td>
</tr> 
</table> <h3 id="Explanation"> Explanation</h3> <div class="t-li1">
<span class="t-li">1)</span> After encountering the <code>#error</code> directive, an implementation displays the message <span class="t-spar">diagnostic-message</span> and renders the program ill-formed (the compilation stops).</div> <div class="t-li1">
<span class="t-li">2)</span> Same as <span class="t-v">(1)</span>, except that the validity of the program is not affected and the compilation continues. </div> <p><span class="t-spar">diagnostic-message</span> can consist of several words not necessarily in quotes.</p>
<h3 id="Notes"> Notes</h3> <p>Before its standardization in C23, <code>#warning</code> has been provided by many compilers in all modes as a conforming extension.</p>
<h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#if __STDC__ != 1
#  error "Not a standard compliant compiler"
#endif
 
#if __STDC_VERSION__ &gt;= 202311L
#  warning "Using #warning as a standard feature"
#endif
 
#include &lt;stdio.h&gt;
int main (void)
{
    printf("The compiler used conforms to the ISO C Standard !!");
}</pre></div> <p>Possible output:</p>
<div class="text source-text"><pre data-language="c">The compiler used conforms to the ISO C Standard !!</pre></div> </div> <h3 id="References"> References</h3>  <ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul><li> 6.10.5 Error directive (p: 126-127) </li></ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 6.10.5 Error directive (p: 174) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 6.10.5 Error directive (p: 159) </li></ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 3.8.5 Error directive </li></ul>
</ul>               <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/preprocessor/error" title="cpp/preprocessor/error">C++ documentation</a></span> for <span class=""><span>Diagnostic directives</span></span> </td>
</tr> </table>           <div class="_attribution">
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