gcc/cp/NEWS

   1 *** Changes in EGCS 1.1:
   2
   3 * Namespaces are fully supported.  The library has not yet been converted
   4   to use namespace std, however, and the old std-faking code is still on by
   5   default.  To turn it off, you can use -fhonor-std.
   6
   7 * Massive template improvements:
   8   + member template classes are supported.
   9   + template friends are supported.
  10   + template template parameters are supported.
  11   + local classes in templates are supported.
  12   + lots of bugs fixed.
  13
  14 * operator new now throws bad_alloc where appropriate.
  15
  16 * Exception handling is now thread safe, and supports nested exceptions and
  17   placement delete.  Exception handling overhead on x86 is much lower with
  18   GNU as 2.9.
  19
  20 * protected virtual inheritance is now supported.
  21
  22 * Loops are optimized better; we now move the test to the end in most
  23   cases, like the C frontend does.
  24
  25 * For class D derived from B which has a member 'int i', &D::i is now of
  26   type 'int B::*' instead of 'int D::*'.
  27
  28 * An _experimental_ new ABI for g++ can be turned on with -fnew-abi.  The
  29   current features of this are more efficient allocation of base classes
  30   (including the empty base optimization), and more compact mangling of C++
  31   symbol names (which can be turned on separately with -fsquangle).  This
  32   ABI is subject to change without notice, so don't use it for anything
  33   that you don't want to rebuild with every release of the compiler.
  34
  35   As with all ABI-changing flags, this flag is for experts only, as all
  36   code (including the library code in libgcc and libstdc++) must be
  37   compiled with the same ABI.
  38
  39 *** Changes in EGCS 1.0:
  40
  41 * A public review copy of the December 1996 Draft of the ISO/ANSI C++
  42   standard is now available. See
  43
  44         http://www.cygnus.com/misc/wp/
  45
  46   for more information.
  47
  48 * g++ now uses a new implementation of templates. The basic idea is that
  49   now templates are minimally parsed when seen and then expanded later.
  50   This allows conformant early name binding and instantiation controls,
  51   since instantiations no longer have to go through the parser.
  52
  53   What you get:
  54
  55      + Inlining of template functions works without any extra effort or
  56        modifications.
  57      + Instantiations of class templates and methods defined in the class
  58        body are deferred until they are actually needed (unless
  59        -fexternal-templates is specified).
  60      + Nested types in class templates work.
  61      + Static data member templates work.
  62      + Member function templates are now supported.
  63      + Partial specialization of class templates is now supported.
  64      + Explicit specification of template parameters to function templates
  65        is now supported.
  66
  67   Things you may need to fix in your code:
  68
  69      + Syntax errors in templates that are never instantiated will now be
  70        diagnosed.
  71      + Types and class templates used in templates must be declared
  72        first, or the compiler will assume they are not types, and fail.
  73      + Similarly, nested types of template type parameters must be tagged
  74        with the 'typename' keyword, except in base lists.  In many cases,
  75        but not all, the compiler will tell you where you need to add
  76        'typename'.  For more information, see
  77
  78             http://www.cygnus.com/misc/wp/dec96pub/template.html#temp.res
  79
  80      + Guiding declarations are no longer supported.  Function declarations,
  81        including friend declarations, do not refer to template instantiations.
  82        You can restore the old behavior with -fguiding-decls until you fix
  83        your code.
  84
  85   Other features:
  86
  87      + Default function arguments in templates will not be evaluated (or
  88        checked for semantic validity) unless they are needed.  Default
  89        arguments in class bodies will not be parsed until the class
  90        definition is complete.
  91      + The -ftemplate-depth-NN flag can be used to increase the maximum
  92        recursive template instantiation depth, which defaults to 17. If you
  93        need to use this flag, the compiler will tell you.
  94      + Explicit instantiation of template constructors and destructors is
  95        now supported.  For instance:
  96
  97             template A<int>::A(const A&);
  98
  99   Still not supported:
 100
 101      + Member class templates.
 102      + Template friends.
 103
 104 * Exception handling support has been significantly improved and is on by
 105   default.  The compiler supports two mechanisms for walking back up the
 106   call stack; one relies on static information about how registers are
 107   saved, and causes no runtime overhead for code that does not throw
 108   exceptions.  The other mechanism uses setjmp and longjmp equivalents, and
 109   can result in quite a bit of runtime overhead.  You can determine which
 110   mechanism is the default for your target by compiling a testcase that
 111   uses exceptions and doing an 'nm' on the object file; if it uses __throw,
 112   it's using the first mechanism.  If it uses __sjthrow, it's using the
 113   second.
 114
 115   You can turn EH support off with -fno-exceptions.
 116
 117 * RTTI support has been rewritten to work properly and is now on by default.
 118   This means code that uses virtual functions will have a modest space
 119   overhead.  You can use the -fno-rtti flag to disable RTTI support.
 120
 121 * On ELF systems, duplicate copies of symbols with 'initialized common'
 122   linkage (such as template instantiations, vtables, and extern inlines)
 123   will now be discarded by the GNU linker, so you don't need to use -frepo.
 124   This support requires GNU ld from binutils 2.8 or later.
 125
 126 * The overload resolution code has been rewritten to conform to the latest
 127   C++ Working Paper.  Built-in operators are now considered as candidates
 128   in operator overload resolution.  Function template overloading chooses
 129   the more specialized template, and handles base classes in type deduction
 130   and guiding declarations properly.  In this release the old code can
 131   still be selected with -fno-ansi-overloading, although this is not
 132   supported and will be removed in a future release.
 133
 134 * Standard usage syntax for the std namespace is supported; std is treated
 135   as an alias for global scope.  General namespaces are still not supported.
 136
 137 * New flags:
 138
 139      + New warning -Wno-pmf-conversion (don't warn about
 140        converting from a bound member function pointer to function
 141        pointer).
 142
 143      + A flag -Weffc++ has been added for violations of some of the style
 144        guidelines in Scott Meyers' _Effective C++_ books.
 145
 146      + -Woverloaded-virtual now warns if a virtual function in a base
 147        class is hidden in a derived class, rather than warning about
 148        virtual functions being overloaded (even if all of the inherited
 149        signatures are overridden) as it did before.
 150
 151      + -Wall no longer implies -W.  The new warning flag, -Wsign-compare,
 152         included in -Wall, warns about dangerous comparisons of signed and
 153         unsigned values. Only the flag is new; it was previously part of
 154         -W.
 155
 156      + The new flag, -fno-weak, disables the use of weak symbols.
 157
 158 * Synthesized methods are now emitted in any translation units that need
 159   an out-of-line copy. They are no longer affected by #pragma interface
 160   or #pragma implementation.
 161
 162 * __FUNCTION__ and __PRETTY_FUNCTION__ are now treated as variables by the
 163   parser; previously they were treated as string constants.  So code like
 164   `printf (__FUNCTION__ ": foo")' must be rewritten to
 165   `printf ("%s: foo", __FUNCTION__)'.  This is necessary for templates.
 166
 167 * local static variables in extern inline functions will be shared between
 168   translation units.
 169
 170 * -fvtable-thunks is supported for all targets, and is the default for
 171   Linux with glibc 2.x (also called libc 6.x).
 172
 173 * bool is now always the same size as another built-in type. Previously,
 174   a 64-bit RISC target using a 32-bit ABI would have 32-bit pointers and a
 175   64-bit bool. This should only affect Irix 6, which was not supported in
 176   2.7.2.
 177
 178 * new (nothrow) is now supported.
 179
 180 * Synthesized destructors are no longer made virtual just because the class
 181   already has virtual functions, only if they override a virtual destructor
 182   in a base class.  The compiler will warn if this affects your code.
 183
 184 * The g++ driver now only links against libstdc++, not libg++; it is
 185   functionally identical to the c++ driver.
 186
 187 * (void *)0 is no longer considered a null pointer constant; NULL in
 188   <stddef.h> is now defined as __null, a magic constant of type (void *)
 189   normally, or (size_t) with -ansi.
 190
 191 * The name of a class is now implicitly declared in its own scope; A::A
 192   refers to A.
 193
 194 * Local classes are now supported.
 195
 196 * __attribute__ can now be attached to types as well as declarations.
 197
 198 * The compiler no longer emits a warning if an ellipsis is used as a
 199   function's argument list.
 200
 201 * Definition of nested types outside of their containing class is now
 202   supported.  For instance:
 203
 204        struct A {
 205               struct B;
 206               B* bp;
 207        };
 208
 209        struct A::B {
 210               int member;
 211        };
 212
 213 * On the HPPA, some classes that do not define a copy constructor
 214   will be passed and returned in memory again so that functions
 215   returning those types can be inlined.
 216
 217 *** The g++ team thanks everyone that contributed to this release,
 218     but especially:
 219
 220 * Joe Buck <jbuck@synopsys.com>, the maintainer of the g++ FAQ.
 221 * Brendan Kehoe <brendan@cygnus.com>, who coordinates testing of g++.
 222 * Jason Merrill <jason@cygnus.com>, the g++ maintainer.
 223 * Mark Mitchell <mmitchell@usa.net>, who implemented member function
 224   templates and explicit qualification of function templates.
 225 * Mike Stump <mrs@wrs.com>, the previous g++ maintainer, who did most of
 226   the exception handling work.