From 9cf11a478df93ab7640e207c7e73f53eba6e36c8 Mon Sep 17 00:00:00 2001 From: Neil Booth Date: Sat, 4 Nov 2000 14:09:28 +0000 Subject: [PATCH] * cpp.texi: Update for _Pragma. From-SVN: r37253 --- gcc/ChangeLog | 4 ++++ gcc/cpp.texi | 65 ++++++++++++++++++++++++++++++++++++--------------- 2 files changed, 50 insertions(+), 19 deletions(-) diff --git a/gcc/ChangeLog b/gcc/ChangeLog index ed341f70d9a..f22013986b9 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,7 @@ +2000-11-04 Neil Booth + + * cpp.texi: Update for _Pragma. + 2000-11-04 Joseph S. Myers * gcc.texi (Contributing): Update URL for projects web page. diff --git a/gcc/cpp.texi b/gcc/cpp.texi index 457cbf2d9b6..b14186a3c02 100644 --- a/gcc/cpp.texi +++ b/gcc/cpp.texi @@ -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 -- 2.30.2