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<h2 class="chapter">8 Other Directives</h2>
<p><a name="index-g_t_0023ident-106"></a><a name="index-g_t_0023sccs-107"></a>The ‘<samp><span class="samp">#ident</span></samp>’ directive takes one argument, a string constant. On
some systems, that string constant is copied into a special segment of
the object file. On other systems, the directive is ignored. The
‘<samp><span class="samp">#sccs</span></samp>’ directive is a synonym for ‘<samp><span class="samp">#ident</span></samp>’.
<p>These directives are not part of the C standard, but they are not
official GNU extensions either. What historical information we have
been able to find, suggests they originated with System V.
<p><a name="index-null-directive-108"></a>The <dfn>null directive</dfn> consists of a ‘<samp><span class="samp">#</span></samp>’ followed by a newline,
with only whitespace (including comments) in between. A null directive
is understood as a preprocessing directive but has no effect on the
preprocessor output. The primary significance of the existence of the
null directive is that an input line consisting of just a ‘<samp><span class="samp">#</span></samp>’ will
produce no output, rather than a line of output containing just a
‘<samp><span class="samp">#</span></samp>’. Supposedly some old C programs contain such lines.
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