const int problem...

const int problem...

[Mark Schaefer]

    Egcs developers,

    Sorry to keep pointing out little annoyances.  (To your credit, the
last one was 100% my stupidity)

According to a co-worker who's studied the proposed standard (I don't
have a copy to reference), Bjarne's third edition is incorrect about how
"const int x = 0" is treated as a class member.  (10.4.6.2)

In a class,

class Curious {
static const int c2 = 11;    // Correct, according to Bjarne
const int c3 = 11;             // Incorrect, according to Bjarne, but
correct according to standard
};

In Bjarne's book this is considered an error, and it seems that egcs
considers it an error as well, i.e. the following code is better:

class Curious {
const int c3;

public:
  Curious() : c3 (5) {}
};

According to the standard, example 1 is better and should  1) take no
space in the actual object, and 2) be implemented like other const's
(direct substitution)

    All this info is second-hand so I'd be very curious as to what the
standard actually says.  My co-worker seemed very convinced, however.
If he's right then code I got this error on is actually correct and
shouldn't be an error:

TgTrackLogId.H:49: warning: ANSI C++ forbids initialization of const
member `undefinedTrackLogId'
TgTrackLogId.H:49: warning: making `undefinedTrackLogId' static


--
Mark Schaefer

Re: const int problem...

[Martin von Loewis]

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> class Curious {
> static const int c2 = 11;    // Correct, according to Bjarne
> const int c3 = 11;             // Incorrect, according to Bjarne, but
> correct according to standard
> };

No, incorrect according to the standard. [class.mem] says about member
syntax:

 member­declarator:
   declarator pure­specifier-opt 
   declarator constant­initializer-opt 
   identifier-opt : constant­expression

 constant­initializer: 
   = constant­expression

Paragraph 4 then says

  A member­declarator can contain a constant­initializer only if it
  declares a static member (9.4) of integral or enumeration type, see
  9.4.2.

»c3« in the example contains a constant-initializer, but it does
not declare a static member (unlike c2), so this is an incorrect
declaration.

Martin

P.S. It took me a while to remember what the last form of
member-declarator declares :-)