*** Changes since EGCS 1.0:
* Namespaces are fully supported. The library has not yet been converted
to use namespace std, however, and the old std-faking code is still on by
default. To turn it off, you can use -fhonor-std.
* Massive template improvements:
+ member template classes are supported.
+ template friends are supported.
+ template template parameters are supported.
+ local classes in templates are supported.
+ lots of bugs fixed.
* operator new now throws bad_alloc where appropriate.
* Exception handling is now thread safe, and supports nested exceptions and
placement delete. Exception handling overhead on x86 is much lower with
GNU as 2.9.
* protected virtual inheritance is now supported.
* Loops are optimized better; we now move the test to the end in most
cases, like the C front end does.
* For class D derived from B which has a member 'int i', &D::i is now of
type 'int B::*' instead of 'int D::*'.
* An _experimental_ new ABI for g++ can be turned on with -fnew-abi. The
current features of this are more efficient allocation of base classes
(including the empty base optimization), and more compact mangling of C++
symbol names (which can be turned on separately with -fsquangle). This
ABI is subject to change without notice, so don't use it for anything
that you don't want to rebuild with every release of the compiler.
As with all ABI-changing flags, this flag is for experts only, as all
code (including the library code in libgcc and libstdc++) must be
compiled with the same ABI.
*** Changes in EGCS 1.0:
* A public review copy of the December 1996 Draft of the ISO/ANSI C++
standard is now available. See
http://www.cygnus.com/misc/wp/
for more information.
* g++ now uses a new implementation of templates. The basic idea is that
now templates are minimally parsed when seen and then expanded later.
This allows conformant early name binding and instantiation controls,
since instantiations no longer have to go through the parser.
What you get:
+ Inlining of template functions works without any extra effort or
modifications.
+ Instantiations of class templates and methods defined in the class
body are deferred until they are actually needed (unless
-fexternal-templates is specified).
+ Nested types in class templates work.
+ Static data member templates work.
+ Member function templates are now supported.
+ Partial specialization of class templates is now supported.
+ Explicit specification of template parameters to function templates
is now supported.
Things you may need to fix in your code:
+ Syntax errors in templates that are never instantiated will now be
diagnosed.
+ Types and class templates used in templates must be declared
first, or the compiler will assume they are not types, and fail.
+ Similarly, nested types of template type parameters must be tagged
with the 'typename' keyword, except in base lists. In many cases,
but not all, the compiler will tell you where you need to add
'typename'. For more information, see
http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
+ Guiding declarations are no longer supported. Function declarations,
including friend declarations, do not refer to template instantiations.
You can restore the old behavior with -fguiding-decls until you fix
your code.
Other features:
+ Default function arguments in templates will not be evaluated (or
checked for semantic validity) unless they are needed. Default
arguments in class bodies will not be parsed until the class
definition is complete.
+ The -ftemplate-depth-NN flag can be used to increase the maximum
recursive template instantiation depth, which defaults to 17. If you
need to use this flag, the compiler will tell you.
+ Explicit instantiation of template constructors and destructors is
now supported. For instance:
template A<int>::A(const A&);
Still not supported:
+ Member class templates.
+ Template friends.
* Exception handling support has been significantly improved and is on by
default. The compiler supports two mechanisms for walking back up the
call stack; one relies on static information about how registers are
saved, and causes no runtime overhead for code that does not throw
exceptions. The other mechanism uses setjmp and longjmp equivalents, and
can result in quite a bit of runtime overhead. You can determine which
mechanism is the default for your target by compiling a testcase that
uses exceptions and doing an 'nm' on the object file; if it uses __throw,
it's using the first mechanism. If it uses __sjthrow, it's using the
second.
You can turn EH support off with -fno-exceptions.
* RTTI support has been rewritten to work properly and is now on by default.
This means code that uses virtual functions will have a modest space
overhead. You can use the -fno-rtti flag to disable RTTI support.
* On ELF systems, duplicate copies of symbols with 'initialized common'
linkage (such as template instantiations, vtables, and extern inlines)
will now be discarded by the GNU linker, so you don't need to use -frepo.
This support requires GNU ld from binutils 2.8 or later.
* The overload resolution code has been rewritten to conform to the latest
C++ Working Paper. Built-in operators are now considered as candidates
in operator overload resolution. Function template overloading chooses
the more specialized template, and handles base classes in type deduction
and guiding declarations properly. In this release the old code can
still be selected with -fno-ansi-overloading, although this is not
supported and will be removed in a future release.
* Standard usage syntax for the std namespace is supported; std is treated
as an alias for global scope. General namespaces are still not supported.
* New flags:
+ New warning -Wno-pmf-conversion (don't warn about
converting from a bound member function pointer to function
pointer).
+ A flag -Weffc++ has been added for violations of some of the style
guidelines in Scott Meyers' _Effective C++_ books.
+ -Woverloaded-virtual now warns if a virtual function in a base
class is hidden in a derived class, rather than warning about
virtual functions being overloaded (even if all of the inherited
signatures are overridden) as it did before.
+ -Wall no longer implies -W. The new warning flag, -Wsign-compare,
included in -Wall, warns about dangerous comparisons of signed and
unsigned values. Only the flag is new; it was previously part of
-W.
+ The new flag, -fno-weak, disables the use of weak symbols.
* Synthesized methods are now emitted in any translation units that need
an out-of-line copy. They are no longer affected by #pragma interface
or #pragma implementation.
* __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
parser; previously they were treated as string constants. So code like
`printf (__FUNCTION__ ": foo")' must be rewritten to
`printf ("%s: foo", __FUNCTION__)'. This is necessary for templates.
* local static variables in extern inline functions will be shared between
translation units.
* -fvtable-thunks is supported for all targets, and is the default for
Linux with glibc 2.x (also called libc 6.x).
* bool is now always the same size as another built-in type. Previously,
a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
64-bit bool. This should only affect Irix 6, which was not supported in
2.7.2.
* new (nothrow) is now supported.
* Synthesized destructors are no longer made virtual just because the class
already has virtual functions, only if they override a virtual destructor
in a base class. The compiler will warn if this affects your code.
* The g++ driver now only links against libstdc++, not libg++; it is
functionally identical to the c++ driver.
* (void *)0 is no longer considered a null pointer constant; NULL in
<stddef.h> is now defined as __null, a magic constant of type (void *)
normally, or (size_t) with -ansi.
* The name of a class is now implicitly declared in its own scope; A::A
refers to A.
* Local classes are now supported.
* __attribute__ can now be attached to types as well as declarations.
* The compiler no longer emits a warning if an ellipsis is used as a
function's argument list.
* Definition of nested types outside of their containing class is now
supported. For instance:
struct A {
struct B;
B* bp;
};
struct A::B {
int member;
};
* On the HPPA, some classes that do not define a copy constructor
will be passed and returned in memory again so that functions
returning those types can be inlined.
*** The g++ team thanks everyone that contributed to this release,
but especially:
* Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
* Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
* Jason Merrill <jason@cygnus.com>, the g++ maintainer.
* Mark Mitchell <mmitchell@usa.net>, who implemented member function
templates and explicit qualification of function templates.
* Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
the exception handling work.
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These pages are maintained by the GCC team. Last modified 2022-10-26.