1 *** Changes in GCC 3.0:
3 * Certain invalid conversions that were previously accepted will now
4 be rejected. For example, assigning function pointers of one type
5 to function pointers of another type now requires a cast, whereas
6 previously g++ would sometimes accept the code even without the
9 * G++ previously allowed `sizeof (X::Y)' where Y was a non-static
10 member of X, even if the `sizeof' expression occurred outside
11 of a non-static member function of X (or one of its derived classes,
12 or a member-initializer for X or one of its derived classes.) This
13 extension has been removed.
15 * G++ no longer allows you to overload the conditional operator (i.e.,
18 *** Changes in GCC 2.95:
20 * Messages about non-conformant code that we can still handle ("pedwarns")
21 are now errors by default, rather than warnings. This can be reverted
22 with -fpermissive, and is overridden by -pedantic or -pedantic-errors.
24 * String constants are now of type `const char[n]', rather than `char[n]'.
25 This can be reverted with -fno-const-strings.
27 * References to functions are now supported.
29 * Lookup of class members during class definition now works in all cases.
31 * In overload resolution, type conversion operators are now properly
32 treated as always coming from the most derived class.
34 * C9x-style restricted pointers are supported, using the `__restrict'
37 * You can now use -fno-implicit-inline-templates to suppress writing out
38 implicit instantiations of inline templates. Normally we do write them
39 out, even with -fno-implicit-templates, so that optimization doesn't
40 affect which instantiations are needed.
42 * -fstrict-prototype now also suppresses implicit declarations.
44 * Many obsolete options have been removed: -fall-virtual, -fmemoize-lookups,
45 -fsave-memoized, +e?, -fenum-int-equivalence, -fno-nonnull-objects.
47 * Unused virtual functions can be discarded on some targets by specifying
48 -ffunction-sections -fvtable-gc to the compiler and --gc-sections to the
49 linker. Unfortunately, this only works on Linux if you're linking
52 * Lots of bugs stomped.
54 *** Changes in EGCS 1.1:
56 * Namespaces are fully supported. The library has not yet been converted
57 to use namespace std, however, and the old std-faking code is still on by
58 default. To turn it off, you can use -fhonor-std.
60 * Massive template improvements:
61 + member template classes are supported.
62 + template friends are supported.
63 + template template parameters are supported.
64 + local classes in templates are supported.
67 * operator new now throws bad_alloc where appropriate.
69 * Exception handling is now thread safe, and supports nested exceptions and
70 placement delete. Exception handling overhead on x86 is much lower with
73 * protected virtual inheritance is now supported.
75 * Loops are optimized better; we now move the test to the end in most
76 cases, like the C frontend does.
78 * For class D derived from B which has a member 'int i', &D::i is now of
79 type 'int B::*' instead of 'int D::*'.
81 * An _experimental_ new ABI for g++ can be turned on with -fnew-abi. The
82 current features of this are more efficient allocation of base classes
83 (including the empty base optimization), and more compact mangling of C++
84 symbol names (which can be turned on separately with -fsquangle). This
85 ABI is subject to change without notice, so don't use it for anything
86 that you don't want to rebuild with every release of the compiler.
88 As with all ABI-changing flags, this flag is for experts only, as all
89 code (including the library code in libgcc and libstdc++) must be
90 compiled with the same ABI.
92 *** Changes in EGCS 1.0:
94 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
95 standard is now available. See
97 http://www.cygnus.com/misc/wp/
101 * g++ now uses a new implementation of templates. The basic idea is that
102 now templates are minimally parsed when seen and then expanded later.
103 This allows conformant early name binding and instantiation controls,
104 since instantiations no longer have to go through the parser.
108 + Inlining of template functions works without any extra effort or
110 + Instantiations of class templates and methods defined in the class
111 body are deferred until they are actually needed (unless
112 -fexternal-templates is specified).
113 + Nested types in class templates work.
114 + Static data member templates work.
115 + Member function templates are now supported.
116 + Partial specialization of class templates is now supported.
117 + Explicit specification of template parameters to function templates
120 Things you may need to fix in your code:
122 + Syntax errors in templates that are never instantiated will now be
124 + Types and class templates used in templates must be declared
125 first, or the compiler will assume they are not types, and fail.
126 + Similarly, nested types of template type parameters must be tagged
127 with the 'typename' keyword, except in base lists. In many cases,
128 but not all, the compiler will tell you where you need to add
129 'typename'. For more information, see
131 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
133 + Guiding declarations are no longer supported. Function declarations,
134 including friend declarations, do not refer to template instantiations.
135 You can restore the old behavior with -fguiding-decls until you fix
140 + Default function arguments in templates will not be evaluated (or
141 checked for semantic validity) unless they are needed. Default
142 arguments in class bodies will not be parsed until the class
143 definition is complete.
144 + The -ftemplate-depth-NN flag can be used to increase the maximum
145 recursive template instantiation depth, which defaults to 17. If you
146 need to use this flag, the compiler will tell you.
147 + Explicit instantiation of template constructors and destructors is
148 now supported. For instance:
150 template A<int>::A(const A&);
154 + Member class templates.
157 * Exception handling support has been significantly improved and is on by
158 default. The compiler supports two mechanisms for walking back up the
159 call stack; one relies on static information about how registers are
160 saved, and causes no runtime overhead for code that does not throw
161 exceptions. The other mechanism uses setjmp and longjmp equivalents, and
162 can result in quite a bit of runtime overhead. You can determine which
163 mechanism is the default for your target by compiling a testcase that
164 uses exceptions and doing an 'nm' on the object file; if it uses __throw,
165 it's using the first mechanism. If it uses __sjthrow, it's using the
168 You can turn EH support off with -fno-exceptions.
170 * RTTI support has been rewritten to work properly and is now on by default.
171 This means code that uses virtual functions will have a modest space
172 overhead. You can use the -fno-rtti flag to disable RTTI support.
174 * On ELF systems, duplicate copies of symbols with 'initialized common'
175 linkage (such as template instantiations, vtables, and extern inlines)
176 will now be discarded by the GNU linker, so you don't need to use -frepo.
177 This support requires GNU ld from binutils 2.8 or later.
179 * The overload resolution code has been rewritten to conform to the latest
180 C++ Working Paper. Built-in operators are now considered as candidates
181 in operator overload resolution. Function template overloading chooses
182 the more specialized template, and handles base classes in type deduction
183 and guiding declarations properly. In this release the old code can
184 still be selected with -fno-ansi-overloading, although this is not
185 supported and will be removed in a future release.
187 * Standard usage syntax for the std namespace is supported; std is treated
188 as an alias for global scope. General namespaces are still not supported.
192 + New warning -Wno-pmf-conversion (don't warn about
193 converting from a bound member function pointer to function
196 + A flag -Weffc++ has been added for violations of some of the style
197 guidelines in Scott Meyers' _Effective C++_ books.
199 + -Woverloaded-virtual now warns if a virtual function in a base
200 class is hidden in a derived class, rather than warning about
201 virtual functions being overloaded (even if all of the inherited
202 signatures are overridden) as it did before.
204 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
205 included in -Wall, warns about dangerous comparisons of signed and
206 unsigned values. Only the flag is new; it was previously part of
209 + The new flag, -fno-weak, disables the use of weak symbols.
211 * Synthesized methods are now emitted in any translation units that need
212 an out-of-line copy. They are no longer affected by #pragma interface
213 or #pragma implementation.
215 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
216 parser; previously they were treated as string constants. So code like
217 `printf (__FUNCTION__ ": foo")' must be rewritten to
218 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
220 * local static variables in extern inline functions will be shared between
223 * -fvtable-thunks is supported for all targets, and is the default for
224 Linux with glibc 2.x (also called libc 6.x).
226 * bool is now always the same size as another built-in type. Previously,
227 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
228 64-bit bool. This should only affect Irix 6, which was not supported in
231 * new (nothrow) is now supported.
233 * Synthesized destructors are no longer made virtual just because the class
234 already has virtual functions, only if they override a virtual destructor
235 in a base class. The compiler will warn if this affects your code.
237 * The g++ driver now only links against libstdc++, not libg++; it is
238 functionally identical to the c++ driver.
240 * (void *)0 is no longer considered a null pointer constant; NULL in
241 <stddef.h> is now defined as __null, a magic constant of type (void *)
242 normally, or (size_t) with -ansi.
244 * The name of a class is now implicitly declared in its own scope; A::A
247 * Local classes are now supported.
249 * __attribute__ can now be attached to types as well as declarations.
251 * The compiler no longer emits a warning if an ellipsis is used as a
252 function's argument list.
254 * Definition of nested types outside of their containing class is now
255 supported. For instance:
266 * On the HPPA, some classes that do not define a copy constructor
267 will be passed and returned in memory again so that functions
268 returning those types can be inlined.
270 *** The g++ team thanks everyone that contributed to this release,
273 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
274 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
275 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
276 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
277 templates and explicit qualification of function templates.
278 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
279 the exception handling work.