1 *** Changes since G++ version 2.7.2:
3 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
4 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 + Explicit specification of template parameters to function templates
29 Things you may need to fix in your code:
31 + Syntax errors in templates that are never instantiated will now be
33 + Types and class templates used in templates must be declared
34 first, or the compiler will assume they are not types, and fail.
35 + Similarly, nested types of template type parameters must be tagged
36 with the 'typename' keyword, except in base lists. In many cases,
37 but not all, the compiler will tell you where you need to add
38 'typename'. For more information, see
40 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
42 + Guiding declarations are no longer supported. Function declarations,
43 including friend declarations, do not refer to template instantiations.
44 You can restore the old behavior with -fguiding-decls until you fix
49 + Default function arguments in templates will not be evaluated (or
50 checked for semantic validity) unless they are needed. Default
51 arguments in class bodies will not be parsed until the class
52 definition is complete.
53 + The -ftemplate-depth-NN flag can be used to increase the maximum
54 recursive template instantiation depth, which defaults to 17. If you
55 need to use this flag, the compiler will tell you.
56 + Explicit instantiation of template constructors and destructors is
57 now supported. For instance:
59 template A<int>::A(const A&);
63 + Member class templates.
64 + Template template parameters.
67 * Exception handling support has been significantly improved and is on by
68 default. The compiler supports two mechanisms for walking back up the
69 call stack; one relies on static information about how registers are
70 saved, and causes no runtime overhead for code that does not throw
71 exceptions. The other mechanism uses setjmp and longjmp equivalents, and
72 can result in quite a bit of runtime overhead. You can determine which
73 mechanism is the default for your target by compiling a testcase that
74 uses exceptions and doing an 'nm' on the object file; if it uses __throw,
75 it's using the first mechanism. If it uses __sjthrow, it's using the
78 You can turn EH support off with -fno-exceptions.
80 * RTTI support has been rewritten to work properly and is now on by default.
81 This means code that uses virtual functions will have a modest space
82 overhead. You can use the -fno-rtti flag to disable RTTI support.
84 * On ELF systems, duplicate copies of symbols with 'initialized common'
85 linkage (such as template instantiations, vtables, and extern inlines)
86 will now be discarded by the GNU linker, so you don't need to use -frepo.
87 This support requires GNU ld from binutils 2.8 or later.
89 * The overload resolution code has been rewritten to conform to the latest
90 C++ Working Paper. Built-in operators are now considered as candidates
91 in operator overload resolution. Function template overloading chooses
92 the more specialized template, and handles base classes in type deduction
93 and guiding declarations properly. In this release the old code can
94 still be selected with -fno-ansi-overloading, although this is not
95 supported and will be removed in a future release.
97 * Standard usage syntax for the std namespace is supported; std is treated
98 as an alias for global scope. General namespaces are still not supported.
102 + New warning -Wno-pmf-conversion (don't warn about
103 converting from a bound member function pointer to function
106 + A flag -Weffc++ has been added for violations of some of the style
107 guidelines in Scott Meyers' _Effective C++_ books.
109 + -Woverloaded-virtual now warns if a virtual function in a base
110 class is hidden in a derived class, rather than warning about
111 virtual functions being overloaded (even if all of the inherited
112 signatures are overridden) as it did before.
114 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
115 included in -Wall, warns about dangerous comparisons of signed and
116 unsigned values. Only the flag is new; it was previously part of
119 + The new flag, -fno-weak, disables the use of weak symbols.
121 * Synthesized methods are now emitted in any translation units that need
122 an out-of-line copy. They are no longer affected by #pragma interface
123 or #pragma implementation.
125 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
126 parser; previously they were treated as string constants. So code like
127 `printf (__FUNCTION__ ": foo")' must be rewritten to
128 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
130 * local static variables in extern inline functions will be shared between
133 * -fvtable-thunks is supported for all targets, and is the default for
134 Linux with glibc 2.x (also called libc 6.x).
136 * bool is now always the same size as another built-in type. Previously,
137 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
138 64-bit bool. This should only affect Irix 6, which was not supported in
141 * new (nothrow) is now supported.
143 * Synthesized destructors are no longer made virtual just because the class
144 already has virtual functions, only if they override a virtual destructor
145 in a base class. The compiler will warn if this affects your code.
147 * The g++ driver now only links against libstdc++, not libg++; it is
148 functionally identical to the c++ driver.
150 * (void *)0 is no longer considered a null pointer constant; NULL in
151 <stddef.h> is now defined as __null, a magic constant of type (void *)
152 normally, or (size_t) with -ansi.
154 * The name of a class is now implicitly declared in its own scope; A::A
157 * Local classes are now supported, though not inside templates.
159 * __attribute__ can now be attached to types as well as declarations.
161 * The compiler no longer emits a warning if an ellipsis is used as a
162 function's argument list.
164 * Definition of nested types outside of their containing class is now
165 supported. For instance:
176 * On the HPPA, some classes that do not define a copy constructor
177 will be passed and returned in memory again so that functions
178 returning those types can be inlined.
180 *** The g++ team thanks everyone that contributed to this release,
183 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
184 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
185 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
186 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
187 templates and explicit qualification of function templates.
188 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
189 the exception handling work.