1 *** Changes in GCC 3.3:
3 * The "new X = 3" extension has been removed; you must now use "new X(3)".
5 *** Changes in GCC 3.1:
7 * -fhonor-std and -fno-honor-std have been removed. -fno-honor-std was
8 a workaround to allow std compliant code to work with the non-std
9 compliant libstdc++-v2. libstdc++-v3 is std compliant.
11 * The C++ ABI has been fixed so that `void (A::*)() const' is mangled as
12 "M1AKFvvE", rather than "MK1AFvvE" as before. This change only affects
13 pointer to cv-qualified member function types.
15 * The C++ ABI has been changed to correctly handle this code:
18 void operator delete[] (void *, size_t);
26 The amount of storage allocated for the array will be greater than
27 it was in 3.0, in order to store the number of elements in the
28 array, so that the correct size can be passed to `operator delete[]'
29 when the array is deleted. Previously, the value passed to
30 `operator delete[]' was unpredictable.
32 This change will only affect code that declares a two-argument
33 `operator delete[]' with a second parameter of type `size_t'
34 in a base class, and does not override that definition in a
37 * The C++ ABI has been changed so that:
40 void operator delete[] (void *, size_t);
41 void operator delete[] (void *);
44 does not cause unnecessary storage to be allocated when an array of
45 `A' objects is allocated.
47 This change will only affect code that declares both of these
48 forms of `operator delete[]', and declared the two-argument form
49 before the one-argument form.
51 * The C++ ABI has been changed so that when a parameter is passed by value,
52 any cleanup for that parameter is performed in the caller, as specified
53 by the ia64 C++ ABI, rather than the called function as before. As a
54 result, classes with a non-trivial destructor but a trivial copy
55 constructor will be passed and returned by invisible reference, rather
56 than by bitwise copy as before.
58 * G++ now supports the "named return value optimization": for code like
66 G++ will allocate 'a' in the return value slot, so that the return
67 becomes a no-op. For this to work, all return statements in the function
68 must return the same variable.
70 *** Changes in GCC 3.0:
72 * Support for guiding declarations has been removed.
74 * G++ now supports importing member functions from base classes with a
77 * G++ now enforces access control for nested types.
79 * In some obscure cases, functions with the same type could have the
80 same mangled name. This bug caused compiler crashes, link-time clashes,
81 and debugger crashes. Fixing this bug required breaking ABI
82 compatibility for the functions involved. The functions in questions
83 are those whose types involve non-type template arguments whose
84 mangled representations require more than one digit.
86 * Support for assignment to `this' has been removed. This idiom
87 was used in the very early days of C++, before users were allowed
88 to overload `operator new'; it is no longer allowed by the C++
91 * Support for signatures, a G++ extension, have been removed.
93 * Certain invalid conversions that were previously accepted will now
94 be rejected. For example, assigning function pointers of one type
95 to function pointers of another type now requires a cast, whereas
96 previously g++ would sometimes accept the code even without the
99 * G++ previously allowed `sizeof (X::Y)' where Y was a non-static
100 member of X, even if the `sizeof' expression occurred outside
101 of a non-static member function of X (or one of its derived classes,
102 or a member-initializer for X or one of its derived classes.) This
103 extension has been removed.
105 * G++ no longer allows you to overload the conditional operator (i.e.,
108 * The "named return value" extension:
110 int f () return r { r = 3; }
112 has been deprecated, and will be removed in a future version of G++.
114 *** Changes in GCC 2.95:
116 * Messages about non-conformant code that we can still handle ("pedwarns")
117 are now errors by default, rather than warnings. This can be reverted
118 with -fpermissive, and is overridden by -pedantic or -pedantic-errors.
120 * String constants are now of type `const char[n]', rather than `char[n]'.
121 This can be reverted with -fno-const-strings.
123 * References to functions are now supported.
125 * Lookup of class members during class definition now works in all cases.
127 * In overload resolution, type conversion operators are now properly
128 treated as always coming from the most derived class.
130 * C9x-style restricted pointers are supported, using the `__restrict'
133 * You can now use -fno-implicit-inline-templates to suppress writing out
134 implicit instantiations of inline templates. Normally we do write them
135 out, even with -fno-implicit-templates, so that optimization doesn't
136 affect which instantiations are needed.
138 * -fstrict-prototype now also suppresses implicit declarations.
140 * Many obsolete options have been removed: -fall-virtual, -fmemoize-lookups,
141 -fsave-memoized, +e?, -fenum-int-equivalence, -fno-nonnull-objects.
143 * Unused virtual functions can be discarded on some targets by specifying
144 -ffunction-sections -fvtable-gc to the compiler and --gc-sections to the
145 linker. Unfortunately, this only works on Linux if you're linking
148 * Lots of bugs stomped.
150 *** Changes in EGCS 1.1:
152 * Namespaces are fully supported. The library has not yet been converted
153 to use namespace std, however, and the old std-faking code is still on by
154 default. To turn it off, you can use -fhonor-std.
156 * Massive template improvements:
157 + member template classes are supported.
158 + template friends are supported.
159 + template template parameters are supported.
160 + local classes in templates are supported.
161 + lots of bugs fixed.
163 * operator new now throws bad_alloc where appropriate.
165 * Exception handling is now thread safe, and supports nested exceptions and
166 placement delete. Exception handling overhead on x86 is much lower with
169 * protected virtual inheritance is now supported.
171 * Loops are optimized better; we now move the test to the end in most
172 cases, like the C frontend does.
174 * For class D derived from B which has a member 'int i', &D::i is now of
175 type 'int B::*' instead of 'int D::*'.
177 * An _experimental_ new ABI for g++ can be turned on with -fnew-abi. The
178 current features of this are more efficient allocation of base classes
179 (including the empty base optimization), and more compact mangling of C++
180 symbol names (which can be turned on separately with -fsquangle). This
181 ABI is subject to change without notice, so don't use it for anything
182 that you don't want to rebuild with every release of the compiler.
184 As with all ABI-changing flags, this flag is for experts only, as all
185 code (including the library code in libgcc and libstdc++) must be
186 compiled with the same ABI.
188 *** Changes in EGCS 1.0:
190 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
191 standard is now available. See
193 http://www.cygnus.com/misc/wp/
195 for more information.
197 * g++ now uses a new implementation of templates. The basic idea is that
198 now templates are minimally parsed when seen and then expanded later.
199 This allows conformant early name binding and instantiation controls,
200 since instantiations no longer have to go through the parser.
204 + Inlining of template functions works without any extra effort or
206 + Instantiations of class templates and methods defined in the class
207 body are deferred until they are actually needed (unless
208 -fexternal-templates is specified).
209 + Nested types in class templates work.
210 + Static data member templates work.
211 + Member function templates are now supported.
212 + Partial specialization of class templates is now supported.
213 + Explicit specification of template parameters to function templates
216 Things you may need to fix in your code:
218 + Syntax errors in templates that are never instantiated will now be
220 + Types and class templates used in templates must be declared
221 first, or the compiler will assume they are not types, and fail.
222 + Similarly, nested types of template type parameters must be tagged
223 with the 'typename' keyword, except in base lists. In many cases,
224 but not all, the compiler will tell you where you need to add
225 'typename'. For more information, see
227 http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
229 + Guiding declarations are no longer supported. Function declarations,
230 including friend declarations, do not refer to template instantiations.
231 You can restore the old behavior with -fguiding-decls until you fix
236 + Default function arguments in templates will not be evaluated (or
237 checked for semantic validity) unless they are needed. Default
238 arguments in class bodies will not be parsed until the class
239 definition is complete.
240 + The -ftemplate-depth-NN flag can be used to increase the maximum
241 recursive template instantiation depth, which defaults to 17. If you
242 need to use this flag, the compiler will tell you.
243 + Explicit instantiation of template constructors and destructors is
244 now supported. For instance:
246 template A<int>::A(const A&);
250 + Member class templates.
253 * Exception handling support has been significantly improved and is on by
254 default. The compiler supports two mechanisms for walking back up the
255 call stack; one relies on static information about how registers are
256 saved, and causes no runtime overhead for code that does not throw
257 exceptions. The other mechanism uses setjmp and longjmp equivalents, and
258 can result in quite a bit of runtime overhead. You can determine which
259 mechanism is the default for your target by compiling a testcase that
260 uses exceptions and doing an 'nm' on the object file; if it uses __throw,
261 it's using the first mechanism. If it uses __sjthrow, it's using the
264 You can turn EH support off with -fno-exceptions.
266 * RTTI support has been rewritten to work properly and is now on by default.
267 This means code that uses virtual functions will have a modest space
268 overhead. You can use the -fno-rtti flag to disable RTTI support.
270 * On ELF systems, duplicate copies of symbols with 'initialized common'
271 linkage (such as template instantiations, vtables, and extern inlines)
272 will now be discarded by the GNU linker, so you don't need to use -frepo.
273 This support requires GNU ld from binutils 2.8 or later.
275 * The overload resolution code has been rewritten to conform to the latest
276 C++ Working Paper. Built-in operators are now considered as candidates
277 in operator overload resolution. Function template overloading chooses
278 the more specialized template, and handles base classes in type deduction
279 and guiding declarations properly. In this release the old code can
280 still be selected with -fno-ansi-overloading, although this is not
281 supported and will be removed in a future release.
283 * Standard usage syntax for the std namespace is supported; std is treated
284 as an alias for global scope. General namespaces are still not supported.
288 + New warning -Wno-pmf-conversion (don't warn about
289 converting from a bound member function pointer to function
292 + A flag -Weffc++ has been added for violations of some of the style
293 guidelines in Scott Meyers' _Effective C++_ books.
295 + -Woverloaded-virtual now warns if a virtual function in a base
296 class is hidden in a derived class, rather than warning about
297 virtual functions being overloaded (even if all of the inherited
298 signatures are overridden) as it did before.
300 + -Wall no longer implies -W. The new warning flag, -Wsign-compare,
301 included in -Wall, warns about dangerous comparisons of signed and
302 unsigned values. Only the flag is new; it was previously part of
305 + The new flag, -fno-weak, disables the use of weak symbols.
307 * Synthesized methods are now emitted in any translation units that need
308 an out-of-line copy. They are no longer affected by #pragma interface
309 or #pragma implementation.
311 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
312 parser; previously they were treated as string constants. So code like
313 `printf (__FUNCTION__ ": foo")' must be rewritten to
314 `printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
316 * local static variables in extern inline functions will be shared between
319 * -fvtable-thunks is supported for all targets, and is the default for
320 Linux with glibc 2.x (also called libc 6.x).
322 * bool is now always the same size as another built-in type. Previously,
323 a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
324 64-bit bool. This should only affect Irix 6, which was not supported in
327 * new (nothrow) is now supported.
329 * Synthesized destructors are no longer made virtual just because the class
330 already has virtual functions, only if they override a virtual destructor
331 in a base class. The compiler will warn if this affects your code.
333 * The g++ driver now only links against libstdc++, not libg++; it is
334 functionally identical to the c++ driver.
336 * (void *)0 is no longer considered a null pointer constant; NULL in
337 <stddef.h> is now defined as __null, a magic constant of type (void *)
338 normally, or (size_t) with -ansi.
340 * The name of a class is now implicitly declared in its own scope; A::A
343 * Local classes are now supported.
345 * __attribute__ can now be attached to types as well as declarations.
347 * The compiler no longer emits a warning if an ellipsis is used as a
348 function's argument list.
350 * Definition of nested types outside of their containing class is now
351 supported. For instance:
362 * On the HPPA, some classes that do not define a copy constructor
363 will be passed and returned in memory again so that functions
364 returning those types can be inlined.
366 *** The g++ team thanks everyone that contributed to this release,
369 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
370 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
371 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
372 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
373 templates and explicit qualification of function templates.
374 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
375 the exception handling work.