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* cpp.texi: Update for _Pragma.

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Neil Booth 2000-11-04 14:09:28 +00:00 committed by Neil Booth
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@ -1,3 +1,7 @@
2000-11-04 Neil Booth <neilb@earthling.net>
* cpp.texi: Update for _Pragma.
2000-11-04 Joseph S. Myers <jsm28@cam.ac.uk>
* gcc.texi (Contributing): Update URL for projects web page.

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@ -2702,17 +2702,8 @@ this is followed by a line number and file name as in @samp{#line}.
@node Other Directives, Output, Line Control, Top
@section Miscellaneous Preprocessing Directives
@cindex null directive
This section describes three additional preprocessing directives. They
are not very useful, but are mentioned for completeness.
The @dfn{null directive} consists of a @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{#} will
produce no output, rather than a line of output containing just a
@samp{#}. Supposedly some old C programs contain such lines.
This section describes some additional, rarely used, preprocessing
directives.
@findex #pragma
@findex #pragma GCC
@ -2730,14 +2721,6 @@ recognized without the @samp{GCC} prefix, however that use is
deprecated. Pragmas that are already deprecated are not recognized with
a @samp{GCC} prefix.
@findex #ident
The @samp{#ident} directive is supported for compatibility with certain
other systems. It is followed by a line of text. On some systems, the
text is copied into a special place in the object file; on most systems,
the text is ignored and this directive has no effect. Typically
@samp{#ident} is only used in header files supplied with those systems
where it is meaningful.
@findex #pragma GCC dependency
The @samp{#pragma GCC dependency} allows you to check the relative dates
of the current file and another file. If the other file is more recent
@ -2752,6 +2735,50 @@ warning message.
#pragma GCC dependency "/usr/include/time.h" rerun /path/to/fixincludes
@end smallexample
@findex _Pragma
The C99 standard also introduces the @samp{_Pragma} operator. The
syntax is @code{_Pragma (string-literal)}, where @samp{string-literal}
can be either a normal or wide-character string literal. It is
destringized, by replacing all @samp{\\} with a single @samp{\} and all
@samp{\"} with a @samp{"}. The result is then processed as if it had
appeared as the right hand side of a @samp{#pragma} directive. For
example,
@smallexample
_Pragma ("GCC dependency \"parse.y\"")
@end smallexample
@noindent has the same effect as @samp{#pragma GCC dependency
"parse.y"}. The same effect could be achieved using macros, for example
@smallexample
#define DO_PRAGMA(x) _Pragma (#x)
DO_PRAGMA (GCC dependency "parse.y")
@end smallexample
The standard is unclear on where a @samp{_Pragma} operator can appear.
The preprocessor accepts it even within a preprocessing conditional
directive like @samp{#if}. To be safe, you are probably best keeping it
out of directives other than @samp{#define}, and putting it on a line of
its own.
@findex #ident
The @samp{#ident} directive is supported for compatibility with certain
other systems. It is followed by a line of text. On some systems, the
text is copied into a special place in the object file; on most systems,
the text is ignored and this directive has no effect. Typically
@samp{#ident} is only used in header files supplied with those systems
where it is meaningful.
@cindex null directive
The @dfn{null directive} consists of a @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{#} will
produce no output, rather than a line of output containing just a
@samp{#}. Supposedly some old C programs contain such lines.
@node Output, Implementation, Other Directives, Top
@section C Preprocessor Output