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