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