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From: lomow@calgary.UUCP (Greg Lomow)
Newsgroups: comp.lang.c++
Subject: :: operator
Message-ID: <900@vaxb.calgary.UUCP>
Date: Sun, 3-May-87 14:00:54 EDT
Article-I.D.: vaxb.900
Posted: Sun May  3 14:00:54 1987
Date-Received: Sun, 10-May-87 09:05:33 EDT
Distribution: na
Organization: U. of Calgary, Calgary, Ab.
Lines: 121

////////////////////////////////////////////////////////////
The following comments apply to the 1.2 release of C++ running
on Unix 4.3BSD.
////////////////////////////////////////////////////////////
/*
The following program defines two functions named func(), one is globally
defined and the other is a member of class cl.
*/

int func()
{ return 1;
}

class cl {
public:
  cl();
  int func();
};

cl::cl()
{ printf("%d %d %d\n", ::func(),	// global function
                         func(),	// member function
                     cl::func());	// member function
}

int cl::func()
{ return 2;
}

main()
{ cl *cl1 = new cl();
  printf("%d %d %d\n", ::func(), 	// global function
                         func(),	// global function
                    cl1->func());	// member function
}

/*
 When I run the program I get the answer I expect
	1 2 2
	1 1 2
*/

////////////////////////////////////////////////////////////
/*
If I modify the program and remove the definition for the 
member function func(), then I would expect the compiler to issue
an error message when it encounters the following line in cl::cl()

                     cl::func());	// member function

Instead the program compiles without error, runs, and produces the
following output
	1 1 1
	1 1

I also tried adding the member function func_test() to see if this problem
was peculiar to constructor functions; once again no error message was
issued.
*/

int func()
{ return 1;
}

class cl {
public:
  cl();
  void func_test();
};

cl::cl()
{ printf("%d %d %d\n", ::func(),	// global function
                         func(),	// global function
                     cl::func());	// member function
}

void cl::func_test()
{ printf("%d %d %d\n", ::func(),	// global function
                         func(),	// global function
                     cl::func());	// member function
}


main()
{ cl *cl1 = new cl();
  cl1->func_test();
  printf("%d %d\n",    ::func(), 	// global function
                         func());	// global function
}

////////////////////////////////////////////////////////////
/*
The reason I expect an error message is that there is no function
with the identifier func() which is a member of the class cl. I see
three possibilities:

1) the :: operator really starts at the qualification level cl and
   looks in cl and its base classes for the definition of func() and
   if it does not find it, :: continues to look for func() in the globally
   defined functions. If this is the case then the semantics of the
   :: operator are not fully explained in the C++ book.

2) This is a bug in the compile time checking that is done in
   conjunction with the :: operator.

3) I don't understand something. Please straighten me out.
*/
////////////////////////////////////////////////////////////
/*
On a separate point, it does not seem to matter to the compiler if I code
	cl *cl1 = new cl;	// NOTE NO '()'
or
	cl *cl1 = new cl();	// NOTE    '()'

Which is correct? or are both ok?
*/
////////////////////////////////////////////////////////////

Greg Lomow

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