1 *** Changes since G++ version 2.7.2:
3 * A public review copy of the December 1996 Draft of the ANSI/ISO C++
4 proto-standard is now available. See
6 http://www.cygnus.com/misc/wp/
10 * g++ now uses a new implementation of templates. The basic idea is that
11 now templates are minimally parsed when seen and then expanded later.
12 This allows conformant early name binding and instantiation controls,
13 since instantiations no longer have to go through the parser.
17 + Inlining of template functions works without any extra effort or
19 + Instantiations of class templates and methods defined in the class
20 body are deferred until they are actually needed (unless
21 -fexternal-templates is specified).
22 + Nested types in class templates work.
23 + Static data member templates work.
24 + Member function templates are now supported.
25 + Partial specialization of class templates is now supported.
26 + The new 'template <>' specialization syntax is now accepted and
28 + Explicit instantiation of template constructors and destructors is
29 now supported. For instance:
31 template A<int>::A(const A&);
33 Things you may need to fix in your code:
35 + Syntax errors in templates that are never instantiated will now be
37 + Types and class templates used in templates must be declared
38 first, or the compiler will assume they are not types, and fail.
39 + Similarly, nested types of template type parameters must be tagged
40 with the 'typename' keyword, except in base lists. In many cases,
41 but not all, the compiler will tell you where you need to add
42 'typename'. For more information, see
44 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
48 + Default function arguments in templates will not be evaluated (or
49 checked for semantic validity) unless they are needed. Default
50 arguments in class bodies will not be parsed until the class
51 definition is complete.
52 + The -ftemplate-depth-NN flag can be used to increase the maximum
53 recursive template instantiation depth, which defaults to 17. If you
54 need to use this flag, the compiler will tell you.
58 + Member class templates.
59 + Template template parameters.
61 + Explicit qualification of function templates.
63 * Exception handling support has been significantly improved and is on by
64 default. This can result in significant runtime overhead. You can turn
65 it off with -fno-exceptions.
67 * RTTI support has been rewritten to work properly and is now on by default.
68 This means code that uses virtual functions will have a modest space
69 overhead. You can use the -fno-rtti flag to disable RTTI support.
71 * On ELF systems, duplicate copies of symbols with 'initialized common'
72 linkage (such as template instantiations, vtables, and extern inlines)
73 will now be discarded by the GNU linker, so you don't need to use -frepo.
74 This support requires GNU ld from binutils 2.8 or later.
76 * The overload resolution code has been rewritten to conform to the latest
77 C++ Working Paper. Built-in operators are now considered as candidates
78 in operator overload resolution. Function template overloading chooses
79 the more specialized template, and handles base classes in type deduction
80 and guiding declarations properly. In this release the old code can
81 still be selected with -fno-ansi-overloading, although this is not
82 supported and will be removed in a future release.
84 * Standard usage syntax for the std namespace is supported; std is treated
85 as an alias for global scope. General namespaces are still not supported.
89 + New flags -Wsign-promo (warn about potentially confusing promotions
90 in overload resolution), -Wno-pmf-conversion (don't warn about
91 converting from a bound member function pointer to function pointer).
93 + A flag -Weffc++ has been added for violations of some of the style
94 guidelines in Scott Meyers' _Effective C++_ books.
96 + -Woverloaded-virtual now warns if a virtual function in a base
97 class is hidden in a derived class, rather than warning about
98 virtual functions being overloaded (even if all of the inherited
99 signatures are overridden) as it did before.
101 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
102 included in -Wall, warns about dangerous comparisons of signed and
103 unsigned values. Only the flag is new; it was previously part of
106 + The new flag, -fno-weak, disables the use of weak symbols.
108 * Synthesized methods are now emitted in any translation units that need
109 an out-of-line copy. They are no longer affected by #pragma interface
110 or #pragma implementation.
112 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
113 parser; previously they were treated as string constants. So code like
114 `printf (__FUNCTION__ ": foo")' must be rewritten to
115 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
117 * local static variables in extern inline functions will be shared between
120 * -fvtable-thunks is supported for all targets, and is the default for
121 Linux with glibc 2.x (also called libc 6.x).
123 * bool is now always the same size as another built-in type. Previously,
124 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
125 64-bit bool. This should only affect Irix 6, which was not supported in
128 * new (nothrow) is now supported.
130 * Synthesized destructors are no longer made virtual just because the class
131 already has virtual functions, only if they override a virtual destructor
132 in a base class. The compiler will warn if this affects your code.
134 * The g++ driver now only links against libstdc++, not libg++; it is
135 functionally identical to the c++ driver.
137 * (void *)0 is no longer considered a null pointer constant; NULL in
138 <stddef.h> is now defined as __null, a magic constant of type (void *)
139 normally, or (size_t) with -ansi.
141 * The name of a class is now implicitly declared in its own scope; A::A
144 * Local classes are now supported.
146 * __attribute__ can now be attached to types as well as declarations.
148 * The compiler no longer emits a warning if an ellipsis is used as a
149 function's argument list.
151 * Definition of nested types outside of their containing class is now
152 supported. For instance:
163 * On the HPPA, some classes that do not define a copy constructor
164 will be passed and returned in memory again so that functions
165 returning those types can be inlined.