Path: utzoo!attcan!uunet!mcsun!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.lang.c++
Subject: Re: Scoping bug???
Summary: A local scope class is really global...
Message-ID: <1729@aber-cs.UUCP>
Date: 13 Apr 90 15:03:24 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 37

In article <2582@ektools.UUCP> randolph@ektools.UUCP (Gary L. Randolph) writes:
  
  Am I missing somthing? Sure smells like a bug.

Reading TFM... :-)

Your example, rewritten in a terser way, goes like this:

	f() { class X { ... }; X localX; ... }
	X globalX;

In C++ it has always been true that the scope of a class name is always
global, modulo redeclarations in inner scopes. In C++ 2.0 the issue of local
scope class definitions has been clarified, in particular with reference to
the problem of member functions defined within the local class definition.
Essentially such class declarations are as though defined in the global
scope, save for some restrictions. Consider the following fragment and try
it on your favourite compiler for some minutes of innocent merryment:

    void f() { struct S { float f; unsigned m() { return this->f == 1.0;} }; }
    struct S s1 = 1.0;
    void g() { struct S { char c; unsigned m() { return this->c == '@'} }; }
    struct S s2 = '@';

    extern "C" extern printf(const char *,...); 

    main() { printf("%u %u\n",s1.m(),s2.m()); return 0; }

Try adding 'struct S;' at the beginning of 'f()' or 'g()', or another
definition of 'struct S' before 'f()'.

Unless you have very clear reasons to use them, stay clear of classes
defined in a block scope.
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk