Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!helios.ee.lbl.gov!pasteur!wenti!brianl
From: brianl@wenti.Berkeley.EDU (Brian Lee)
Newsgroups: comp.lang.c++
Subject: Correction to Re: Default constructor, unexpected call
Keywords: constructor
Message-ID: <26655@pasteur.Berkeley.EDU>
Date: 1 Aug 90 19:21:00 GMT
Sender: news@pasteur.Berkeley.EDU
Reply-To: brianl@wenti.Berkeley.EDU (Brian Lee)
Lines: 56
X-Local-Date: 1 Aug 90 12:21:00 PDT

Many thanks to Brian Kennedy <bmk@dux.csc.ti.com> for kindly
pointing out that my example in Article 8944 really does produce
correct results.  This is just another example of a computer doing
what you told it to do instead of what you wanted it to do. :-)

In my example, the default constructors for superclasses are called
because my specification of the subclass copy constructor replaces
the default component-wise initialization that would have been
generated and by omission of explicit base initialization specifies
that the default constructors should be used.

For example, the classes

class X {
public:
    X()         { cout << "default X::X()\n"; }
    X(const X&) { cout << "copy X::X(const X&)\n"; }
};

class Y : public X {
public:
    Y()         { cout << "default Y::Y()\n"; }
//    Y(const Y&)       { cout << "copy Y::Y(const Y&)\n"; }
};

class Z : public Y {
public:
    Z()         { cout << "default Z::Z()\n"; }
    Z(const Z&) { cout << "copy Z::Z(const Z&)\n"; }
};

should really have been defined as

class X {
public:
    X()         { cout << "default X::X()\n"; }
    X(const X&) { cout << "copy X::X(const X&)\n"; }
};

class Y : public X {
public:
    Y()         { cout << "default Y::Y()\n"; }
//    Y(const Y& y) : X(y)       { cout << "copy Y::Y(const Y&)\n"; }
};

class Z : public Y {
public:
    Z()         		{ cout << "default Z::Z()\n"; }
    Z(const Z& z) : Y(z)	{ cout << "copy Z::Z(const Z&)\n"; }
};

The revised definitions work fine.

Sorry for any confusion this may have caused.

Brian Lee