cpp: Other Directives

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1 8 Other Directives
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1 The '#ident' directive takes one argument, a string constant.  On some
1 systems, that string constant is copied into a special segment of the
1 object file.  On other systems, the directive is ignored.  The '#sccs'
1 directive is a synonym for '#ident'.
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1    These directives are not part of the C standard, but they are not
1 official GNU extensions either.  What historical information we have
1 been able to find, suggests they originated with System V.
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1    The "null directive" consists of a '#' followed by a newline, with
1 only whitespace (including comments) in between.  A null directive is
1 understood as a preprocessing directive but has no effect on the
1 preprocessor output.  The primary significance of the existence of the
1 null directive is that an input line consisting of just a '#' will
1 produce no output, rather than a line of output containing just a '#'.
1 Supposedly some old C programs contain such lines.
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