176 lines
6.9 KiB
Plaintext
176 lines
6.9 KiB
Plaintext
*** Changes since G++ version 2.7.2:
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* A public review copy of the December 1996 Draft of the ANSI/ISO C++
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proto-standard is now available. See
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http://www.cygnus.com/misc/wp/
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for more information.
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* g++ now uses a new implementation of templates. The basic idea is that
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now templates are minimally parsed when seen and then expanded later.
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This allows conformant early name binding and instantiation controls,
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since instantiations no longer have to go through the parser.
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What you get:
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+ Inlining of template functions works without any extra effort or
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modifications.
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+ Instantiations of class templates and methods defined in the class
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body are deferred until they are actually needed (unless
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-fexternal-templates is specified).
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+ Nested types in class templates work.
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+ Static data member templates work.
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+ Member function templates are now supported.
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+ Partial specialization of class templates is now supported.
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+ The new 'template <>' specialization syntax is now accepted and
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ignored.
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+ Explicit instantiation of template constructors and destructors is
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now supported. Use the following source code, as an example.
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template A<int>::A(const A&);
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Possible problems (caused by complying with the ANSI/ISO draft):
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+ Types and class templates used in templates must be declared
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first, or the compiler will assume they are not types, and fail.
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+ Similarly, nested types of template type parameters must be tagged
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with the 'typename' keyword. In many cases, the compiler will tell
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you where you need to add 'typename'.
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+ Syntax errors in templates that are never instantiated will now be
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diagnosed.
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Other features:
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+ Default function arguments in templates will not be evaluated (or
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checked for semantic validity) unless they are needed. Default
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arguments in class bodies will not be parsed until the class
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definition is complete.
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+ The -ftemplate-depth-NN flag can be used to increase the maximum
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recursive template instantiation depth, defaulting to 17. If you need
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to use this flag, the compiler will tell you.
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Still not supported:
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+ Template template parameters.
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* Exception handling support has been significantly improved and is on by
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default. This can result in significant runtime overhead. You can turn
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it off with -fno-exceptions.
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* Synthesized methods are now emitted in any translation units that need
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an out-of-line copy. They are no longer affected by #pragma interface
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or #pragma implementation.
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* On ELF systems, duplicate copies of symbols with 'initialized common'
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linkage (such as template instantiations, vtables, and extern inlines)
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will now be discarded by the GNU linker, so you don't need to use -frepo.
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This support requires GNU ld from binutils 2.8 or later.
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* __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
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parser; previously they were treated as string constants. So code like
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`printf (__FUNCTION__ ": foo")' must be rewritten to
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`printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
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* New flags:
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+ New flags -Wsign-promo (warn about potentially confusing promotions
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in overload resolution), -Wno-pmf-conversion (don't warn about
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converting from a bound member function pointer to function pointer).
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+ A flag -Weffc++ has been added for violations of some of the style
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guidelines in Scott Meyers' _Effective C++_ books.
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+ -Woverloaded-virtual now warns if a virtual function in a base
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class is hidden in a derived class, rather than warning about
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virtual functions being overloaded (even if all of the inherited
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signatures are overridden) as it did before.
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+ -Wall no longer implies -W. The new warning flag, -Wsign-compare,
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included in -Wall, warns about dangerous comparisons of signed and
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unsigned values. Only the flag is new; it was previously part of
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-W.
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+ The new flag, -fno-weak, disables the use of weak symbols.
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* local static variables in extern inline functions will be shared between
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translation units.
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* Standard usage syntax for the std namespace is supported; std is treated
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as an alias for global scope. General namespaces are still not supported.
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* -fvtable-thunks is supported for all targets, and is the default for
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Linux with glibc 2.x (also called libc 6.x).
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* RTTI support has been rewritten to work properly and is now on by default.
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This means code that uses virtual functions will have a modest space
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overhead. You can use the -fno-rtti flag to disable RTTI support.
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* The internal interface between RTTI-using code and the RTTI support
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library has changed, so code that uses dynamic_cast should be
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recompiled. The RTTI support library has moved from libstdc++ to
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libgcc, so you no longer need to link against libstdc++ for a program
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that doesn't use the "hosted" library.
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* bool is now always the same size as another built-in type. Previously,
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a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
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64-bit bool. This should only affect Irix 6, which was not supported in
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2.7.2.
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* new (nothrow) is now supported.
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* The overload resolution code has been rewritten to conform to the latest
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C++ Working Paper. Built-in operators are now considered as candidates
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in operator overload resolution. Function template overloading chooses
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the more specialized template, and handles base classes in type deduction
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and guiding declarations properly. In this release the old code can
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still be selected with -fno-ansi-overloading, although this is not
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supported and will be removed in a future release.
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* Synthesized destructors are no longer made virtual just because the class
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already has virtual functions, only if they override a virtual destructor
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in a base class. The compiler will warn if this affects your code.
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* The g++ driver now only links against libstdc++, not libg++; it is
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functionally identical to the c++ driver.
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* (void *)0 is no longer considered a null pointer constant; NULL in
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<stddef.h> is now defined as __null, a magic constant of type (void *)
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normally, or (size_t) with -ansi.
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* The name of a class is now implicitly declared in its own scope; A::A
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refers to A.
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* Local classes are now supported.
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* __attribute__ can now be attached to types as well as declarations.
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* The compiler no longer emits a warning if an ellipsis is used as a
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function's argument list.
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* Definition of nested types outside of their containing class is now
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supported. Use the following source code, as an example.
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struct A {
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struct B;
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B* bp;
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};
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struct A::B {
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int member;
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};
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* On the HPPA, some classes that do not define a copy constructor
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will be passed and returned in memory again so that functions
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returning those types can be inlined.
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