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Small web / my contrib update
- From: Neil Booth <neil at daikokuya dot demon dot co dot uk>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Gerald Pfeifer <pfeifer at dbai dot tuwien dot ac dot at>
- Date: Mon, 13 May 2002 22:36:47 +0100
- Subject: Small web / my contrib update
I was reading bugs.html today and noticed an out-of-date claim.
Fixed below. Also, I thought I'd update my contribution text
a bit as I've done a lot more than cpplib now 8-)
OK to commit?
* wwwdocs/htdocs/bugs.html: Update re directives in macros.
* contrib.texi: Update my entry.
RCS file: /cvs/gcc/gcc/gcc/doc/contrib.texi,v
retrieving revision 1.25
diff -u -p -r1.25 contrib.texi
--- gcc/doc/contrib.texi 30 Apr 2002 13:32:03 -0000 1.25
+++ gcc/doc/contrib.texi 13 May 2002 21:32:32 -0000
@@ -38,7 +38,8 @@ Alasdair Baird for various bugfixes.
Gerald Baumgartner added the signature extension to the C++ front end.
-Neil Booth for various work on cpplib.
+Neil Booth for work on cpplib, lang hooks, debug hooks and other
Per Bothner for his direction via the steering committee and various
RCS file: /cvs/gcc/wwwdocs/htdocs/bugs.html,v
retrieving revision 1.54
diff -u -p -r1.54 bugs.html
--- wwwdocs/htdocs/bugs.html 1 May 2002 16:35:25 -0000 1.54
+++ wwwdocs/htdocs/bugs.html 13 May 2002 21:32:34 -0000
@@ -368,42 +368,21 @@ test.c:10: undefined or invalid # direct
test.c:11: parse error before `#'<br />
-<p>The problem, simply put, is that GCC's preprocessor does not allow you
-to put <code>#ifdef</code> (or any other directive) inside the arguments of
-a macro. Your C library's <code><string.h></code> happens to
-define <code>memcpy</code> as a macro - this is perfectly legitimate.
-The code therefore will not compile.</p>
-<p>We have two good reasons for not allowing directives inside
-macro arguments. First, it is not portable. It is "undefined
-behavior" according to the C standard; that means different
-compilers will do different things with it. Some will give you
-errors. Some will dump core. Some will silently mangle your code -
-you could get the equivalent of</p>
- memcpy(dest, src, 1224);
-<p>from the above example. A very few might do what you expected it
-to. We therefore feel it is most useful for GCC to reject this
-construct immediately so that it is found and fixed.</p>
+<p><strong>Update:</strong> As of GCC 3.2 this kind of construct is
+always accepted and CPP will probably do what you expect, but see the
+manual for detailed semantics.</p>
-<p>Second, it is extraordinarily difficult to implement the
-preprocessor such that it does what you would expect for every
-possible directive found inside a macro argument. The best example is
-#define foo(arg) ... arg ...<br />
-#undef foo<br />
-<p>which is <em>impossible</em> to implement in portable C without
-leaking memory. Allowing only a subset of directives would be
+<p>However, versions of GCC prior to 3.2 did not allow you to put
+<code>#ifdef</code> (or any other directive) inside the arguments of a
+macro. Your C library's <code><string.h></code> happens to
+define <code>memcpy</code> as a macro - this is perfectly legitimate.
+The code therefore would not compile.</p>
-<p>It is always possible to rewrite code which uses conditionals
-inside macros so that it doesn't. You could write the above
+<p>This kind of code is not portable. It is "undefined behavior"
+according to the C standard; that means different compilers will do
+different things with it. It is always possible to rewrite code which
+uses conditionals inside macros so that it doesn't. You could write
+the above example</p>
#ifdef PLATFORM1<br />
memcpy(dest, src, 12);<br />