1 *** Changes in GCC 3.0.1:
3 * -fhonor-std and -fno-honor-std have been removed. -fno-honor-std was
4 a workaround to allow std compliant code to work with the non-std
5 compliant libstdc++-v2. libstdc++-v3 is std compliant.
7 *** Changes in GCC 3.0:
9 * Support for guiding declarations has been removed.
11 * G++ now supports importing member functions from base classes with a
14 * G++ now enforces access control for nested types.
16 * In some obscure cases, functions with the same type could have the
17 same mangled name. This bug caused compiler crashes, link-time clashes,
18 and debugger crashes. Fixing this bug required breaking ABI
19 compatibility for the functions involved. The functions in questions
20 are those whose types involve non-type template arguments whose
21 mangled representations require more than one digit.
23 * Support for assignment to `this' has been removed. This idiom
24 was used in the very early days of C++, before users were allowed
25 to overload `operator new'; it is no longer allowed by the C++
28 * Support for signatures, a G++ extension, have been removed.
30 * Certain invalid conversions that were previously accepted will now
31 be rejected. For example, assigning function pointers of one type
32 to function pointers of another type now requires a cast, whereas
33 previously g++ would sometimes accept the code even without the
36 * G++ previously allowed `sizeof (X::Y)' where Y was a non-static
37 member of X, even if the `sizeof' expression occurred outside
38 of a non-static member function of X (or one of its derived classes,
39 or a member-initializer for X or one of its derived classes.) This
40 extension has been removed.
42 * G++ no longer allows you to overload the conditional operator (i.e.,
45 * The "named return value" extension:
47 int f () return r { r = 3; }
49 has been deprecated, and will be removed in a future version of G++.
51 *** Changes in GCC 2.95:
53 * Messages about non-conformant code that we can still handle ("pedwarns")
54 are now errors by default, rather than warnings. This can be reverted
55 with -fpermissive, and is overridden by -pedantic or -pedantic-errors.
57 * String constants are now of type `const char[n]', rather than `char[n]'.
58 This can be reverted with -fno-const-strings.
60 * References to functions are now supported.
62 * Lookup of class members during class definition now works in all cases.
64 * In overload resolution, type conversion operators are now properly
65 treated as always coming from the most derived class.
67 * C9x-style restricted pointers are supported, using the `__restrict'
70 * You can now use -fno-implicit-inline-templates to suppress writing out
71 implicit instantiations of inline templates. Normally we do write them
72 out, even with -fno-implicit-templates, so that optimization doesn't
73 affect which instantiations are needed.
75 * -fstrict-prototype now also suppresses implicit declarations.
77 * Many obsolete options have been removed: -fall-virtual, -fmemoize-lookups,
78 -fsave-memoized, +e?, -fenum-int-equivalence, -fno-nonnull-objects.
80 * Unused virtual functions can be discarded on some targets by specifying
81 -ffunction-sections -fvtable-gc to the compiler and --gc-sections to the
82 linker. Unfortunately, this only works on Linux if you're linking
85 * Lots of bugs stomped.
87 *** Changes in EGCS 1.1:
89 * Namespaces are fully supported. The library has not yet been converted
90 to use namespace std, however, and the old std-faking code is still on by
91 default. To turn it off, you can use -fhonor-std.
93 * Massive template improvements:
94 + member template classes are supported.
95 + template friends are supported.
96 + template template parameters are supported.
97 + local classes in templates are supported.
100 * operator new now throws bad_alloc where appropriate.
102 * Exception handling is now thread safe, and supports nested exceptions and
103 placement delete. Exception handling overhead on x86 is much lower with
106 * protected virtual inheritance is now supported.
108 * Loops are optimized better; we now move the test to the end in most
109 cases, like the C frontend does.
111 * For class D derived from B which has a member 'int i', &D::i is now of
112 type 'int B::*' instead of 'int D::*'.
114 * An _experimental_ new ABI for g++ can be turned on with -fnew-abi. The
115 current features of this are more efficient allocation of base classes
116 (including the empty base optimization), and more compact mangling of C++
117 symbol names (which can be turned on separately with -fsquangle). This
118 ABI is subject to change without notice, so don't use it for anything
119 that you don't want to rebuild with every release of the compiler.
121 As with all ABI-changing flags, this flag is for experts only, as all
122 code (including the library code in libgcc and libstdc++) must be
123 compiled with the same ABI.
125 *** Changes in EGCS 1.0:
127 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
128 standard is now available. See
130 http://www.cygnus.com/misc/wp/
132 for more information.
134 * g++ now uses a new implementation of templates. The basic idea is that
135 now templates are minimally parsed when seen and then expanded later.
136 This allows conformant early name binding and instantiation controls,
137 since instantiations no longer have to go through the parser.
141 + Inlining of template functions works without any extra effort or
143 + Instantiations of class templates and methods defined in the class
144 body are deferred until they are actually needed (unless
145 -fexternal-templates is specified).
146 + Nested types in class templates work.
147 + Static data member templates work.
148 + Member function templates are now supported.
149 + Partial specialization of class templates is now supported.
150 + Explicit specification of template parameters to function templates
153 Things you may need to fix in your code:
155 + Syntax errors in templates that are never instantiated will now be
157 + Types and class templates used in templates must be declared
158 first, or the compiler will assume they are not types, and fail.
159 + Similarly, nested types of template type parameters must be tagged
160 with the 'typename' keyword, except in base lists. In many cases,
161 but not all, the compiler will tell you where you need to add
162 'typename'. For more information, see
164 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
166 + Guiding declarations are no longer supported. Function declarations,
167 including friend declarations, do not refer to template instantiations.
168 You can restore the old behavior with -fguiding-decls until you fix
173 + Default function arguments in templates will not be evaluated (or
174 checked for semantic validity) unless they are needed. Default
175 arguments in class bodies will not be parsed until the class
176 definition is complete.
177 + The -ftemplate-depth-NN flag can be used to increase the maximum
178 recursive template instantiation depth, which defaults to 17. If you
179 need to use this flag, the compiler will tell you.
180 + Explicit instantiation of template constructors and destructors is
181 now supported. For instance:
183 template A<int>::A(const A&);
187 + Member class templates.
190 * Exception handling support has been significantly improved and is on by
191 default. The compiler supports two mechanisms for walking back up the
192 call stack; one relies on static information about how registers are
193 saved, and causes no runtime overhead for code that does not throw
194 exceptions. The other mechanism uses setjmp and longjmp equivalents, and
195 can result in quite a bit of runtime overhead. You can determine which
196 mechanism is the default for your target by compiling a testcase that
197 uses exceptions and doing an 'nm' on the object file; if it uses __throw,
198 it's using the first mechanism. If it uses __sjthrow, it's using the
201 You can turn EH support off with -fno-exceptions.
203 * RTTI support has been rewritten to work properly and is now on by default.
204 This means code that uses virtual functions will have a modest space
205 overhead. You can use the -fno-rtti flag to disable RTTI support.
207 * On ELF systems, duplicate copies of symbols with 'initialized common'
208 linkage (such as template instantiations, vtables, and extern inlines)
209 will now be discarded by the GNU linker, so you don't need to use -frepo.
210 This support requires GNU ld from binutils 2.8 or later.
212 * The overload resolution code has been rewritten to conform to the latest
213 C++ Working Paper. Built-in operators are now considered as candidates
214 in operator overload resolution. Function template overloading chooses
215 the more specialized template, and handles base classes in type deduction
216 and guiding declarations properly. In this release the old code can
217 still be selected with -fno-ansi-overloading, although this is not
218 supported and will be removed in a future release.
220 * Standard usage syntax for the std namespace is supported; std is treated
221 as an alias for global scope. General namespaces are still not supported.
225 + New warning -Wno-pmf-conversion (don't warn about
226 converting from a bound member function pointer to function
229 + A flag -Weffc++ has been added for violations of some of the style
230 guidelines in Scott Meyers' _Effective C++_ books.
232 + -Woverloaded-virtual now warns if a virtual function in a base
233 class is hidden in a derived class, rather than warning about
234 virtual functions being overloaded (even if all of the inherited
235 signatures are overridden) as it did before.
237 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
238 included in -Wall, warns about dangerous comparisons of signed and
239 unsigned values. Only the flag is new; it was previously part of
242 + The new flag, -fno-weak, disables the use of weak symbols.
244 * Synthesized methods are now emitted in any translation units that need
245 an out-of-line copy. They are no longer affected by #pragma interface
246 or #pragma implementation.
248 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
249 parser; previously they were treated as string constants. So code like
250 `printf (__FUNCTION__ ": foo")' must be rewritten to
251 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
253 * local static variables in extern inline functions will be shared between
256 * -fvtable-thunks is supported for all targets, and is the default for
257 Linux with glibc 2.x (also called libc 6.x).
259 * bool is now always the same size as another built-in type. Previously,
260 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
261 64-bit bool. This should only affect Irix 6, which was not supported in
264 * new (nothrow) is now supported.
266 * Synthesized destructors are no longer made virtual just because the class
267 already has virtual functions, only if they override a virtual destructor
268 in a base class. The compiler will warn if this affects your code.
270 * The g++ driver now only links against libstdc++, not libg++; it is
271 functionally identical to the c++ driver.
273 * (void *)0 is no longer considered a null pointer constant; NULL in
274 <stddef.h> is now defined as __null, a magic constant of type (void *)
275 normally, or (size_t) with -ansi.
277 * The name of a class is now implicitly declared in its own scope; A::A
280 * Local classes are now supported.
282 * __attribute__ can now be attached to types as well as declarations.
284 * The compiler no longer emits a warning if an ellipsis is used as a
285 function's argument list.
287 * Definition of nested types outside of their containing class is now
288 supported. For instance:
299 * On the HPPA, some classes that do not define a copy constructor
300 will be passed and returned in memory again so that functions
301 returning those types can be inlined.
303 *** The g++ team thanks everyone that contributed to this release,
306 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
307 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
308 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
309 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
310 templates and explicit qualification of function templates.
311 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
312 the exception handling work.