From: khan AT xraylith DOT wisc DOT edu (Mumit Khan) Subject: Re: Cygwin32 & C++ standard 31 Dec 1997 17:22:30 -0800 Message-ID: <9801010055.AA26764.cygnus.gnu-win32@modi.xraylith.wisc.edu> References: <3 DOT 0 DOT 1 DOT 32 DOT 19971231165103 DOT 0069dfec AT elwood DOT pionet DOT net> To: Justin Hopkins Cc: gnu-win32 AT cygnus DOT com Justin Hopkins writes: > Can someone give me an idea of how conforming cygwin32 is > to the C++ standard? Or at least to the December '96 public > draft? Thanks Depends on what you mean by cygwin32 C++. If you mean the original b18 distribution, it's horribly old, so all bets are off if you're looking at the latest draft that was approved as the standard. On the other hand, the egcs distribution is pretty close, and in fact, close enough to (almost) compete with some top quality commercial compilers such as Kai and others based on the EDG front end. Also note that G++ now uses unmodified SGI STL distribution, which means that as SGI updates its implementation to match the standard, G++ will follow automatically. Here're some quotes from the latest cp/NEWS (my commens are within [[ ]]): * g++ now uses a new implementation of templates. The basic idea is that now templates are minimally parsed when seen and then expanded later. This allows conformant early name binding and instantiation controls, since instantiations no longer have to go through the parser. What you get: + Inlining of template functions works without any extra effort or modifications. + Instantiations of class templates and methods defined in the class body are deferred until they are actually needed (unless -fexternal-templates is specified). + Nested types in class templates work. + Static data member templates work. + Member function templates are now supported. + Partial specialization of class templates is now supported. + Explicit specification of template parameters to function templates is now supported. [[ also, now you don't have to worry about instantiatng templates yourself on ELF and PE-COFF, since the linker will simply discard the duplicates. In fact, I've seen 25% size reduction in final code size that until now used explicit template instantiation in conjunction with -fno-impliction-template flag ]] Things you may need to fix in your code: + Syntax errors in templates that are never instantiated will now be diagnosed. + Types and class templates used in templates must be declared first, or the compiler will assume they are not types, and fail. + Similarly, nested types of template type parameters must be tagged with the 'typename' keyword, except in base lists. In many cases, but not all, the compiler will tell you where you need to add 'typename'. For more information, see http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res + Guiding declarations are no longer supported. Function declarations, including friend declarations, do not refer to template instantiations. You can restore the old behavior with -fguiding-decls until you fix your code. [[ The last one will catch lot of existing code, and using -fguiding-decls is really no good since that can cause trouble with library code, especially iostreams. The right solution is to convert your code correctly, and if you need backward compatibility with older compilers, you can use preprocess macros. For an example of how to do this using autoconf, take a look at my patch to GNU Octave 2.0.9 available at: ftp://ftp.xraylith.wisc.edu/pub/khan/gnu-win32/cygwin32/ports/ ]] Other features: + Default function arguments in templates will not be evaluated (or checked for semantic validity) unless they are needed. Default arguments in class bodies will not be parsed until the class definition is complete. + The -ftemplate-depth-NN flag can be used to increase the maximum recursive template instantiation depth, which defaults to 17. If you need to use this flag, the compiler will tell you. + Explicit instantiation of template constructors and destructors is now supported. For instance: template A::A(const A&); Still not supported: + Member class templates. + Template template parameters. + Template friends. [[ Not having Template friends stink, but since I'm not about contribute the code, I can't really complain. The next one in line that I'd like is the Template template parameters, since I have tons of code that uses this feature, and there is not easy work-around. I can do without the member class templates feature since there are easy work-arounds. ]] [[ Also not implemented is namespaces, but at least code that uses just std namespace will work. ]] * Standard usage syntax for the std namespace is supported; std is treated as an alias for global scope. General namespaces are still not supported. [[ Other things like RTTI, exception handling work quite well. On platforms where Dwarf2 unwinding works well, EH work like a charm; on others, such as win32, where it doesn't yet, g++ uses setjmp-longjmp, which imposes space and time penalty when using EH. ]] [[ Two more items that can potentially break existing code: ]] * The overload resolution code has been rewritten to conform to the latest C++ Working Paper. Built-in operators are now considered as candidates in operator overload resolution. Function template overloading chooses the more specialized template, and handles base classes in type deduction and guiding declarations properly. In this release the old code can still be selected with -fno-ansi-overloading, although this is not supported and will be removed in a future release. * (void *)0 is no longer considered a null pointer constant; NULL in is now defined as __null, a magic constant of type (void *) normally, or (size_t) with -ansi. Happy New Year Mumit -- khan AT xraylith DOT wisc DOT edu http://www.xraylith.wisc.edu/~khan/ - For help on using this list (especially unsubscribing), send a message to "gnu-win32-request AT cygnus DOT com" with one line of text: "help".