1 *** Changes in GCC 3.1:
3 * G++ previously allowed attributes in some places that it should not have,
6 S s (7) __attribute__ ((init_priority (3)));
8 The attributes should come after the declarator, as in:
10 S s __attribute__ ((init_priority (3))) s (7);
12 The old syntax is no longer allowed.
14 * Support for anachronistic initialization in constructors, e.g.:
23 * Support for named return values has been removed.
25 * Support for initializer lists in new-expressions, e.g.:
31 * -fhonor-std and -fno-honor-std have been removed. -fno-honor-std was
32 a workaround to allow std compliant code to work with the non-std
33 compliant libstdc++-v2. libstdc++-v3 is std compliant.
35 * The C++ ABI has been changed to correctly handle this code:
38 void operator delete[] (void *, size_t);
46 The amount of storage allocated for the array will be greater than
47 it was in 3.0, in order to store the number of elements in the
48 array, so that the correct size can be passed to `operator delete[]'
49 when the array is deleted. Previously, the value passed to
50 `operator delete[]' was unpredictable.
52 This change will only affect code that declares a two-argument
53 `operator delete[]' with a second parameter of type `size_t'
54 in a base class, and does not override that definition in a
57 * The C++ ABI has been changed so that:
60 void operator delete[] (void *, size_t);
61 void operator delete[] (void *);
64 does not cause unncessary storage to be allocated when an array of
65 `A' objects is allocated.
67 This change will only affect code that declares both of these
68 forms of `operator delete[]', and declared the two-argument form
69 before the one-argument form.
71 *** Changes in GCC 3.0:
73 * Support for guiding declarations has been removed.
75 * G++ now supports importing member functions from base classes with a
78 * G++ now enforces access control for nested types.
80 * In some obscure cases, functions with the same type could have the
81 same mangled name. This bug caused compiler crashes, link-time clashes,
82 and debugger crashes. Fixing this bug required breaking ABI
83 compatibility for the functions involved. The functions in questions
84 are those whose types involve non-type template arguments whose
85 mangled representations require more than one digit.
87 * Support for assignment to `this' has been removed. This idiom
88 was used in the very early days of C++, before users were allowed
89 to overload `operator new'; it is no longer allowed by the C++
92 * Support for signatures, a G++ extension, have been removed.
94 * Certain invalid conversions that were previously accepted will now
95 be rejected. For example, assigning function pointers of one type
96 to function pointers of another type now requires a cast, whereas
97 previously g++ would sometimes accept the code even without the
100 * G++ previously allowed `sizeof (X::Y)' where Y was a non-static
101 member of X, even if the `sizeof' expression occurred outside
102 of a non-static member function of X (or one of its derived classes,
103 or a member-initializer for X or one of its derived classes.) This
104 extension has been removed.
106 * G++ no longer allows you to overload the conditional operator (i.e.,
109 * The "named return value" extension:
111 int f () return r { r = 3; }
113 has been deprecated, and will be removed in a future version of G++.
115 *** Changes in GCC 2.95:
117 * Messages about non-conformant code that we can still handle ("pedwarns")
118 are now errors by default, rather than warnings. This can be reverted
119 with -fpermissive, and is overridden by -pedantic or -pedantic-errors.
121 * String constants are now of type `const char[n]', rather than `char[n]'.
122 This can be reverted with -fno-const-strings.
124 * References to functions are now supported.
126 * Lookup of class members during class definition now works in all cases.
128 * In overload resolution, type conversion operators are now properly
129 treated as always coming from the most derived class.
131 * C9x-style restricted pointers are supported, using the `__restrict'
134 * You can now use -fno-implicit-inline-templates to suppress writing out
135 implicit instantiations of inline templates. Normally we do write them
136 out, even with -fno-implicit-templates, so that optimization doesn't
137 affect which instantiations are needed.
139 * -fstrict-prototype now also suppresses implicit declarations.
141 * Many obsolete options have been removed: -fall-virtual, -fmemoize-lookups,
142 -fsave-memoized, +e?, -fenum-int-equivalence, -fno-nonnull-objects.
144 * Unused virtual functions can be discarded on some targets by specifying
145 -ffunction-sections -fvtable-gc to the compiler and --gc-sections to the
146 linker. Unfortunately, this only works on Linux if you're linking
149 * Lots of bugs stomped.
151 *** Changes in EGCS 1.1:
153 * Namespaces are fully supported. The library has not yet been converted
154 to use namespace std, however, and the old std-faking code is still on by
155 default. To turn it off, you can use -fhonor-std.
157 * Massive template improvements:
158 + member template classes are supported.
159 + template friends are supported.
160 + template template parameters are supported.
161 + local classes in templates are supported.
162 + lots of bugs fixed.
164 * operator new now throws bad_alloc where appropriate.
166 * Exception handling is now thread safe, and supports nested exceptions and
167 placement delete. Exception handling overhead on x86 is much lower with
170 * protected virtual inheritance is now supported.
172 * Loops are optimized better; we now move the test to the end in most
173 cases, like the C frontend does.
175 * For class D derived from B which has a member 'int i', &D::i is now of
176 type 'int B::*' instead of 'int D::*'.
178 * An _experimental_ new ABI for g++ can be turned on with -fnew-abi. The
179 current features of this are more efficient allocation of base classes
180 (including the empty base optimization), and more compact mangling of C++
181 symbol names (which can be turned on separately with -fsquangle). This
182 ABI is subject to change without notice, so don't use it for anything
183 that you don't want to rebuild with every release of the compiler.
185 As with all ABI-changing flags, this flag is for experts only, as all
186 code (including the library code in libgcc and libstdc++) must be
187 compiled with the same ABI.
189 *** Changes in EGCS 1.0:
191 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
192 standard is now available. See
194 http://www.cygnus.com/misc/wp/
196 for more information.
198 * g++ now uses a new implementation of templates. The basic idea is that
199 now templates are minimally parsed when seen and then expanded later.
200 This allows conformant early name binding and instantiation controls,
201 since instantiations no longer have to go through the parser.
205 + Inlining of template functions works without any extra effort or
207 + Instantiations of class templates and methods defined in the class
208 body are deferred until they are actually needed (unless
209 -fexternal-templates is specified).
210 + Nested types in class templates work.
211 + Static data member templates work.
212 + Member function templates are now supported.
213 + Partial specialization of class templates is now supported.
214 + Explicit specification of template parameters to function templates
217 Things you may need to fix in your code:
219 + Syntax errors in templates that are never instantiated will now be
221 + Types and class templates used in templates must be declared
222 first, or the compiler will assume they are not types, and fail.
223 + Similarly, nested types of template type parameters must be tagged
224 with the 'typename' keyword, except in base lists. In many cases,
225 but not all, the compiler will tell you where you need to add
226 'typename'. For more information, see
228 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
230 + Guiding declarations are no longer supported. Function declarations,
231 including friend declarations, do not refer to template instantiations.
232 You can restore the old behavior with -fguiding-decls until you fix
237 + Default function arguments in templates will not be evaluated (or
238 checked for semantic validity) unless they are needed. Default
239 arguments in class bodies will not be parsed until the class
240 definition is complete.
241 + The -ftemplate-depth-NN flag can be used to increase the maximum
242 recursive template instantiation depth, which defaults to 17. If you
243 need to use this flag, the compiler will tell you.
244 + Explicit instantiation of template constructors and destructors is
245 now supported. For instance:
247 template A<int>::A(const A&);
251 + Member class templates.
254 * Exception handling support has been significantly improved and is on by
255 default. The compiler supports two mechanisms for walking back up the
256 call stack; one relies on static information about how registers are
257 saved, and causes no runtime overhead for code that does not throw
258 exceptions. The other mechanism uses setjmp and longjmp equivalents, and
259 can result in quite a bit of runtime overhead. You can determine which
260 mechanism is the default for your target by compiling a testcase that
261 uses exceptions and doing an 'nm' on the object file; if it uses __throw,
262 it's using the first mechanism. If it uses __sjthrow, it's using the
265 You can turn EH support off with -fno-exceptions.
267 * RTTI support has been rewritten to work properly and is now on by default.
268 This means code that uses virtual functions will have a modest space
269 overhead. You can use the -fno-rtti flag to disable RTTI support.
271 * On ELF systems, duplicate copies of symbols with 'initialized common'
272 linkage (such as template instantiations, vtables, and extern inlines)
273 will now be discarded by the GNU linker, so you don't need to use -frepo.
274 This support requires GNU ld from binutils 2.8 or later.
276 * The overload resolution code has been rewritten to conform to the latest
277 C++ Working Paper. Built-in operators are now considered as candidates
278 in operator overload resolution. Function template overloading chooses
279 the more specialized template, and handles base classes in type deduction
280 and guiding declarations properly. In this release the old code can
281 still be selected with -fno-ansi-overloading, although this is not
282 supported and will be removed in a future release.
284 * Standard usage syntax for the std namespace is supported; std is treated
285 as an alias for global scope. General namespaces are still not supported.
289 + New warning -Wno-pmf-conversion (don't warn about
290 converting from a bound member function pointer to function
293 + A flag -Weffc++ has been added for violations of some of the style
294 guidelines in Scott Meyers' _Effective C++_ books.
296 + -Woverloaded-virtual now warns if a virtual function in a base
297 class is hidden in a derived class, rather than warning about
298 virtual functions being overloaded (even if all of the inherited
299 signatures are overridden) as it did before.
301 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
302 included in -Wall, warns about dangerous comparisons of signed and
303 unsigned values. Only the flag is new; it was previously part of
306 + The new flag, -fno-weak, disables the use of weak symbols.
308 * Synthesized methods are now emitted in any translation units that need
309 an out-of-line copy. They are no longer affected by #pragma interface
310 or #pragma implementation.
312 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
313 parser; previously they were treated as string constants. So code like
314 `printf (__FUNCTION__ ": foo")' must be rewritten to
315 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
317 * local static variables in extern inline functions will be shared between
320 * -fvtable-thunks is supported for all targets, and is the default for
321 Linux with glibc 2.x (also called libc 6.x).
323 * bool is now always the same size as another built-in type. Previously,
324 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
325 64-bit bool. This should only affect Irix 6, which was not supported in
328 * new (nothrow) is now supported.
330 * Synthesized destructors are no longer made virtual just because the class
331 already has virtual functions, only if they override a virtual destructor
332 in a base class. The compiler will warn if this affects your code.
334 * The g++ driver now only links against libstdc++, not libg++; it is
335 functionally identical to the c++ driver.
337 * (void *)0 is no longer considered a null pointer constant; NULL in
338 <stddef.h> is now defined as __null, a magic constant of type (void *)
339 normally, or (size_t) with -ansi.
341 * The name of a class is now implicitly declared in its own scope; A::A
344 * Local classes are now supported.
346 * __attribute__ can now be attached to types as well as declarations.
348 * The compiler no longer emits a warning if an ellipsis is used as a
349 function's argument list.
351 * Definition of nested types outside of their containing class is now
352 supported. For instance:
363 * On the HPPA, some classes that do not define a copy constructor
364 will be passed and returned in memory again so that functions
365 returning those types can be inlined.
367 *** The g++ team thanks everyone that contributed to this release,
370 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
371 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
372 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
373 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
374 templates and explicit qualification of function templates.
375 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
376 the exception handling work.