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<title>The C Preprocessor: Other Directives</title>
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Next: <a href="Preprocessor-Output.html#Preprocessor-Output" accesskey="n" rel="next">Preprocessor Output</a>, Previous: <a href="Pragmas.html#Pragmas" accesskey="p" rel="prev">Pragmas</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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<a name="Other-Directives-1"></a>
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<h2 class="chapter">8 Other Directives</h2>
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<a name="index-_0023ident"></a>
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<a name="index-_0023sccs"></a>
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<p>The ‘<samp>#ident</samp>’ directive takes one argument, a string constant. On
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some systems, that string constant is copied into a special segment of
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the object file. On other systems, the directive is ignored. The
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‘<samp>#sccs</samp>’ directive is a synonym for ‘<samp>#ident</samp>’.
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</p>
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<p>These directives are not part of the C standard, but they are not
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official GNU extensions either. What historical information we have
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been able to find, suggests they originated with System V.
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</p>
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<a name="index-null-directive"></a>
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<p>The <em>null directive</em> consists of a ‘<samp>#</samp>’ followed by a newline,
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with only whitespace (including comments) in between. A null directive
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is understood as a preprocessing directive but has no effect on the
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preprocessor output. The primary significance of the existence of the
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null directive is that an input line consisting of just a ‘<samp>#</samp>’ will
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produce no output, rather than a line of output containing just a
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‘<samp>#</samp>’. Supposedly some old C programs contain such lines.
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