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From: warsaw@nlm.nih.gov (Barry A. Warsaw)
Newsgroups: comp.lang.c++
Subject: Scope in static member initialization? (New C++'er Alert :-)
Message-ID: <WARSAW.90Dec4123403@warsaw.nlm.nih.gov>
Date: 4 Dec 90 17:34:03 GMT
Sender: news@cme.nist.gov
Reply-To: warsaw@nlm.nih.gov
Organization: Century Computing, Inc.
Lines: 71


I have a question about scope and access permissions in the
initialization of static class members.  In the code following my
siggy, I've got a program with 2 classes: first and second.  Class
second contains a static data member of type first, which is
initialized on the line:

	first second::one = ( 9 );

Now, if the constructor for class first is public, everything compiles
and works fine.  However, if the constructor is protected, the
compiler complains with:

	error:  ..() cannot access first::first(): protected  member

even though class second is made a friend of class first (which
*should* give it access to first's protected members, right?). Unless
this is a bug in the compiler, I obviously have a misunderstanding
about scope and access in this situation. Is the error because this
initialization is being done at file scope, which doesn't have access
to first's protected member?  I haven't been able to find a definitive
answer in the books I've read.  Forget, for the moment, why I'd want
to have a protected constructor for class first.

For the record I'm using Sun's C++ (CC -v produces: Sun C++ 2.0 FCS -
10/20/89), on an SS1+.  Compile the following program as is to produce
the error, or with -DPROTECT=public to eliminate the error.

Could someone please explain exactly what the problem is, and how to
correct it while still keeping first's constructor protected?  Or tell
me why it *must* be public for this to have meaning. Thanks for your
help. 

-Barry

NAME:  Barry A. Warsaw         INET: warsaw@nlm.nih.gov
TELE:  (301) 496-1936          UUCP: uunet!nlm.nih.gov!warsaw

======================================================================

#include <stream.h>

#ifndef PROTECT
#define PROTECT protected
#endif

class first {
	friend class second;
	int cnt;
PROTECT:
	first( int c=1 ) { cnt = c; }
public:
	int count() { return( cnt ); }
	};


class second {
	static first one;
	int cnt;
public:
	second() { cnt = 1; }
	int count() { return( one.count() ); }
	};


first second::one = ( 9 );

main() {
	second foo;
	cout << "foo: " << foo.count() << "\n";
	};


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