Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c++
Subject: Re: HELP: default constructor for array of class
Keywords: constructor, default, class, array, definition
Message-ID: <701@taumet.com>
Date: 3 May 91 15:46:03 GMT
References: <1991May2.165955.28385@iitmax.iit.edu>
Organization: Taumetric Corporation, San Diego
Lines: 34

chien@iitmax.iit.edu (Greg Chien) writes:

>When compiling the following program, C++ complains that Point::Point()
>default constructor is not found in resolving Point p[2].  However,
>if Point() { x = 200; } is uncommented, ambiguous constructors error
>is generated in resolving Point q.

>class Point {
>	...
>public:
>//	Point() { x = 200; }
>	Point(int xc = 100) { x = xc; }
>};
>	Point p[2];

A default constructor is required to initialize the array 'p'.  Under
the latest language rules, any constructor requiring no parameters
(such as 'Point(int=100);') will serve, but this is also noted as
a recent extension.  With future compilers, the could should work
as given.  With many current compilers (including Borland C++ 2.0)
the 'Point()' constructor is required, as that was the earlier rule.

But the combination
	Point();
	Point(int = 100);
is ambiguous, since neither constructor needs to be called with any
parameters.  You can achieve exactly the effect of your original code
by using
	Point() { x = 100; }
	Point(int xc) { x = xc; }
This satisfies both old and new language rules.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com