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