reno.texi

gcc库的原代码,对编程有很大帮助.

class B @{ @dots{} @};
void f (A<B>);
@end example

Under @samp{-fexternal-templates}, the definition of @samp{A<B>} ends up
in the implementation file that includes @file{a.h}.  Under
@samp{-falt-external-templates}, the same definition ends up in the
implementation file that includes @file{b.h}.

@item
You can control explicitly where a template is instantiated, without
having to @emph{use} the template to get an instantiation.  

To instantiate a class template explicitly, write @samp{template
class @var{name}<paramvals>}, where @var{paramvals} is a list of values
for the template parameters.  For example, you might write

@example
template class A<int>
@end example

Similarly, to instantiate a function template explicitly, write
@samp{template @var{fnsign}} where @var{fnsign} is the particular
function signature you need.  For example, you might write

@example
template void foo (int, int)
@end example

This syntax for explicit template instantiation agrees with recent
extensions to the draft @sc{ansi} standard.

@item
The compiler's actions on @sc{ansi}-related warnings and errors have
been further enhanced.  The @samp{-pedantic-errors} option produces
error messages in a number of new situations: using @code{return} in a
non-@code{void} function (one returning a value); declaring a local
variable that shadows a parameter (e.g., the function takes an argument
@samp{a}, and has a local variable @samp{a}); and use of the @samp{asm}
keyword.  Finally, the compiler by default now issues a warning when
converting from an @code{int} to an enumerated type.  This is likely to
cause many new warnings in code that hadn't triggered them before.  For
example, when you compile this code,

@smallexample
@group
enum boolean @{ false, true @};
void
f ()
@{
  boolean x;

  x = 1; //@i{assigning an @code{int} to an @code{enum} now triggers a warning}
@}
@end group
@end smallexample

@noindent
you should see the warning ``@code{anachronistic conversion from integer
type to enumeral type `boolean'}''.  Instead of assigning the value 1,
assign the original enumerated value @samp{true}.
@end itemize

@node Enhancements and bug fixes
@section Enhancements and bug fixes

@itemize @bullet
@cindex nested types in template parameters
@item
You can now use nested types in a template parameter list, even if the nested
type is defined within the same class that attempts to use the template.
For example, given a template @code{list}, the following now works:

@smallexample
struct glyph @{
  @dots{}
  struct stroke @{ @dots{} @};
  list<stroke> l;
  @dots{}
@}
@end smallexample

@cindex function pointers vs template parameters
@item
Function pointers now work in template parameter lists.  For
example, you might want to instantiate a parameterized @code{list} class
in terms of a pointer to a function like this:

@smallexample
list<int (*)(int, void *)> fnlist;
@end smallexample

@item
@c FIXME!  Really no limit?  Jason said "deeper than 9" now OK...
Nested types are now handled correctly.  In particular, there is no
longer a limit to how deeply you can nest type definitions.

@item
@sc{gnu} C++ now conforms to the specifications in Chapter 11 of the
@sc{arm}, ``Member Access Control''.

@item
The @sc{ansi} C++ committee has introduced a new keyword @code{mutable}.
@sc{gnu} C++ supports it.  Use @code{mutable} to specify that some
particular members of a @code{const} class are @emph{not} constant.  For
example, you can use this to include a cache in a data structure that
otherwise represents a read-only database.

@item
Error messages now explicitly specify the declaration, type, or
expression that contains an error.

@item
To avoid copying and editing all system include files during @sc{gnu}
C++ installation, the compiler now automatically recognizes system
include files as C language definitions, as if they were wrapped in
@samp{extern "C" @{ @dots{} @}}.

@item
The compiler checks operator declarations more strictly.  For example,
you may no longer declare an @samp{operator +} with three arguments.

@item
You can now use template type arguments in the same template
parameter list where the type argument is specified (as well as in the
template body).  For example, you may write

@example
template <class T, T t> class A @{ @dots{} @};
@end example

@item
Destructors are now available for all types, even built-in ones; for
example, you can call @samp{int::~int}.  (Destructors for types like
@code{int} do not actually do anything, but their existence provides a
level of generality that permits smooth template expansion in more
cases.)

@item
Enumerated types declared inside a class are now handled correctly.

@item
An argument list for a function may not use an initializer list for its default
value.  For example, @w{@samp{void foo ( T x = @{ 1, 2 @} )}} is not permitted.

@item
A significant amount of work went into improving the ability of the
compiler to act accurately on multiple inheritance and virtual
functions.  Virtual function dispatch has been enhanced as well.

@item
The warning concerning a virtual inheritance environment with a
non-virtual destructor has been disabled, since it is not clear that
such a warning is warranted.

@item
Until exception handling is fully implemented in the Reno-2 release, use
of the identifiers @samp{catch}, @samp{throw}, or @samp{try} results
in the warning:

@smallexample
t.C:1: warning: `catch', `throw', and `try' 
       are all C++ reserved words
@end smallexample

@item
When giving a warning or error concerning initialization of a member in a
class, the compiler gives the name of the member if it has one.

@item
Detecting friendship between classes is more accurately checked.

@item
The syntaxes of @w{@samp{#pragma implementation "file.h"}} and
@samp{#pragma interface} are now more strictly controlled.  The compiler
notices (and warns) when any text follows @file{file.h} in the
implementation pragma, or follows the word @samp{interface}.  Any such
text is otherwise ignored.

@item
Trying to declare a template on a variable or type is now considered an
error, not an unimplemented feature.

@item
When an error occurs involving a template, the compiler attempts to
tell you at which point of instantiation the error occurred, in
addition to noting the line in the template declaration which had the
actual error.

@item
The symbol names for function templates in the resulting assembly file
are now encoded according to the arguments, rather than just being
emitted as, for example, two definitions of a function @samp{foo}.

@item
Template member functions that are declared @code{static} no longer
receive a @code{this} pointer.

@item
Case labels are no longer allowed to have commas to make up their
expressions.

@item
Warnings concerning the shift count of a left or right shift now tell
you if it was a @samp{left} or @samp{right} shift.

@item
The compiler now warns when a decimal constant is so large that it
becomes @code{unsigned}.

@item
Union initializers which are raw constructors are now handled properly.

@item
The compiler no longer gives incorrect errors when initializing a
union with an empty initializer list.

@item
Anonymous unions are now correctly used when nested inside a class.

@item
Anonymous unions declared as static class members are now handled
properly.

@item
The compiler now notices when a field in a class is declared both as
a type and a non-type.

@item
The compiler now warns when a user-defined function shadows a
built-in function, rather than emitting an error.

@item
A conflict between two function declarations now produces an error
regardless of their language context.

@item
Duplicate definitions of variables with @samp{extern "C"} linkage are no
longer considered in error.  (Note in C++ linkage---the default---you may
not have more than one definition of a variable.)

@item
Referencing a label that is not defined in any function is now an error.

@item
The syntax for pointers to methods has been improved; there are still
some minor bugs, but a number of cases should now be accepted by the
compiler.

@item
In error messages, arguments are now numbered starting at 1, instead of
0.  Therefore, in the function @samp{void foo (int a, int b)}, the
argument @samp{a} is argument 1, and @samp{b} is argument 2.  There is
no longer an argument 0.

@item
The tag for an enumerator, rather than its value, used as a default
argument is now shown in all error messages.  For example, @w{@samp{void
foo (enum x (= true))}} is shown instead of @w{@samp{void foo (enum x (=
1))}}.

@item
The @samp{__asm__} keyword is now accepted by the C++ front-end.

@item
Expressions of the form @samp{foo->~Class()} are now handled properly.

@item
The compiler now gives better warnings for situations which result in
integer overflows (e.g., in storage sizes, enumerators, unary
expressions, etc).

@item
@code{unsigned} bitfields are now promoted to @code{signed int} if the
field isn't as wide as an @code{int}.

@item
Declaration and usage of prefix and postfix @samp{operator ++} and
@samp{operator --} are now handled correctly.  For example,

@smallexample
@group
class foo
@{
public:
  operator ++ ();
  operator ++ (int);
  operator -- ();
  operator -- (int);
@};

void
f (foo *f)
@{
  f++;          // @i{call @code{f->operator++(int)}}
  ++f;          // @i{call @code{f->operator++()}}
  f--;          // @i{call @code{f->operator++(int)}}
  --f;          // @i{call @code{f->operator++()}}
@}
@end group
@end smallexample

@item
In accordance with @sc{arm} section 10.1.1, ambiguities and dominance are now
handled properly.  The rules described in section 10.1.1 are now fully
implemented. 

@end itemize

@node Problems with debugging
@section Problems with debugging

Two problems remain with regard to debugging:

@itemize @bullet
@item
Debugging of anonymous structures on the IBM RS/6000 host is incorrect.

@item
Symbol table size is overly large due to redundant symbol information;
this can make @code{gdb} coredump under certain circumstances.  This
problem is not host-specific.
@end itemize

@node Plans
@chapter Plans for Reno-2

The overall goal for the second phase of the @sc{gnu} C++ Renovation
Project is to bring @sc{gnu} C++ to a new level of reliability, quality,
and competitiveness.  As particular elements of this strategy, we intend
to:

@enumerate 0
@item
Fully implement @sc{ansi} exception handling.

@item
With the exception handling, add Runtime Type Identification
(@sc{rtti}), if the @sc{ansi} committee adopts it into the standard.

@item
Bring the compiler into closer compliance with the @sc{arm} and the draft
@sc{ansi} standard, and document what points in the @sc{arm} we do not yet comply,
or agree, with.

@item
Add further support for the @sc{dwarf} debugging format.

@item
Finish the work to make the compiler compliant with @sc{arm} Section 12.6.2,
initializing base classes in declaration order, rather than in the order
that you specify them in a @var{mem-initializer} list.

@item
Perform a full coverage analysis on the compiler, and weed out unused
code, for a gain in performance and a reduction in the size of the compiler.

@item
Further improve the multiple inheritance implementation in the
compiler to make it cleaner and more complete.
@end enumerate

@noindent
As always, we encourage you to make suggestions and ask questions about
@sc{gnu} C++ as a whole, so we can be sure that the end of this project
will bring a compiler that everyone will find essential for C++ and will
meet the needs of the world's C++ community.

@include templates.texi

@include gpcompare.texi

@contents

@bye