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