| Message ID | 20160211175933.GE3163@redhat.com |
|---|---|
| State | New |
| Headers | show |
>> struct X { >> const static double i = 3.14; >> }; >> >> error: floating-point literal cannot appear in a constant-expression >> const static double i = 3.14; >> ^~~~ > > Hm, indeed; I hadn't notice that. Dunno if is a bug (clang++ accepts this > with a warning). I've added ", provided the initializer is an integer", > that should be enough. I don't think documenting this as a blanket restriction is right. The code is silently accepted without -Wpedantic and few people use the option so the added text would be misleading as is. But my feeling is that this is just a bug, in which case I wouldn't expect to see it documented in any case. > > Somehow I knew you'd have something to add here ;). How about this then? The flexible array addition looks great to me. Thank you! Martin
On Thu, Feb 11, 2016 at 11:45:37AM -0700, Martin Sebor wrote: > >> struct X { > >> const static double i = 3.14; > >> }; > >> > >> error: floating-point literal cannot appear in a constant-expression > >> const static double i = 3.14; > >> ^~~~ > > > >Hm, indeed; I hadn't notice that. Dunno if is a bug (clang++ accepts this > >with a warning). I've added ", provided the initializer is an integer", > >that should be enough. > > I don't think documenting this as a blanket restriction is right. > The code is silently accepted without -Wpedantic and few people > use the option so the added text would be misleading as is. But > my feeling is that this is just a bug, in which case I wouldn't > expect to see it documented in any case. Ok, I'll drop that note then. > The flexible array addition looks great to me. Thank you! Great. I'll commit the patch. Marek
>> The flexible array addition looks great to me. Thank you! > > Great. I'll commit the patch. Actually, there is one other thing that might be wort mentioning about flexible array members. The type and mangling of flexible array members has changed. While in GCC 5 and prior the type of a flexible array member is an array of zero elements (a GCC extension), in 6 it is that of an array of an unspecified bound (i.e., T[] as opposed to T[0]). This is a silent ABI change with no -fabi-version/-Wabi option. Martin
On Thu, Feb 11, 2016 at 01:36:49PM -0700, Martin Sebor wrote: > >>The flexible array addition looks great to me. Thank you! > > > >Great. I'll commit the patch. > > Actually, there is one other thing that might be wort mentioning > about flexible array members. > > The type and mangling of flexible array members has changed. While > in GCC 5 and prior the type of a flexible array member is an array > of zero elements (a GCC extension), in 6 it is that of an array of > an unspecified bound (i.e., T[] as opposed to T[0]). This is > a silent ABI change with no -fabi-version/-Wabi option. Aha. I think you're better-suited to document this than I am. Marek
Index: porting_to.html =================================================================== RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-6/porting_to.html,v retrieving revision 1.9 diff -u -r1.9 porting_to.html --- porting_to.html 10 Feb 2016 17:21:54 -0000 1.9 +++ porting_to.html 11 Feb 2016 17:58:43 -0000 @@ -269,6 +269,53 @@ to port the code to use C++11's <code>std::unique_ptr</code> instead. </p> +<h3>'constexpr' needed for in-class initialization of static data member</h3> + +<p> +Since C++11, the <code>constexpr</code> keyword is needed when initializing a +non-integral static data member in a class. As a GNU extension, the following +program is accepted in C++03 (albeit with a <tt>-Wpedantic</tt> warning), +provided the initializer is an integer: +</p> + +<pre><code> +struct X { + const static double i = 10; +}; +</pre></code> + +<p> +The C++11 standard supports that in-class initialization using +<code>constexpr</code> instead, so the GNU extension is no longer supported for +C++11 or later. Programs relying on the extension will be rejected with an +error. The fix is to use <code>constexpr</code> instead of <code>const</code>. +</p> + +<h3>Stricter flexible array member rules</h3> + +<p> +As of this release, the C++ compiler is now more strict about flexible array +member rules. As a consequence, the following code is no longer accepted: +</p> + +<pre><code> +union U { + int i; + char a[]; +}; +</pre></code> + +<p> +Furthermore, the C++ compiler now rejects structures with a flexible array +member as the only member: +</p> + +<pre><code> +struct S { + char a[]; +}; +</pre></code> + <h2>-Wmisleading-indentation</h2> <p> A new warning <code>-Wmisleading-indentation</code> was added