Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!ucsd!rutgers!bellcore!faline!thumper!ulysses!andante!alice!bs
From: bs@alice.UUCP (Bjarne Stroustrup)
Newsgroups: comp.lang.c++
Subject: Re: Default initializations for class constructors
Summary: a bug
Keywords: c++
Message-ID: <8184@alice.UUCP>
Date: 10 Sep 88 01:31:19 GMT
References: <684@paris.ICS.UCI.EDU>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 58



bonnie.ics.uci.edu
 University of California, Irvine - Dept. of ICS)

 > Hi,

 >   Can someone please enlighten me as to the correct behavior of C++
 > when class constructors with different argument types are all declared
 > to have default parameter initializers?  My basic question is, which
 > of the constructors should be selected if the type is not clear from
 > the definition of a class object?  G++ appears to use the first
 > lexically presented constructor as the default, is this specified, or
 > is the behavior undefined in the language?

No, the implicit call of (some) foo::foo() from bar::bar() is ambiguous
and therefore clearly an error. Cfront gets it wrong too, though. Sorry.

	- Bjarne

 > #include <stream.h>
 > 
 > class foo {
 >    int i;
 > public:
 >    foo(double j = 10.5) {
 >       i = int(j) * 5;
 >       cout << "double constructor\n";
 >    }   
 >    foo(int j = 10) {
 >       i = j;
 >       cout << "int constructor\n";
 >    }
 >    int Tell() {
 >       return i;
 >    }   
 > };
 > 
 > class bar : public foo {
 >    int i;
 > public:
 >    bar(void) {
 >       i = foo::Tell();
 >    }
 >    int Tell(void) {
 >       return i;
 >    }
 > };
 > 
 > main() {
 >    bar Foo;
 >    cout << Foo.Tell() << "\n";
 >    // G++ prints out 50 at this point, indicating that it called
 >    // the double constructor as default.
 > }

 > thanks for any help on this matter,

 >     Doug Schmidt