Path: utzoo!attcan!ncrcan!scocan!jfischer
From: jfischer@sco.COM (Jonathan Fischer)
Newsgroups: comp.lang.c++
Subject: Re: `new'ing an object that has a constructor
Message-ID: <1990Jul13.115822.17803@sco.COM>
Date: 13 Jul 90 15:58:22 GMT
References: <5137@castle.ed.ac.uk>
Reply-To: jfischer@sco.COM (Jonathan Fischer)
Organization: SCO Canada, Inc. (formerly HCR Corporation)
Lines: 38

In article <5137@castle.ed.ac.uk> ecsv38@castle.ed.ac.uk (S Manoharan) writes:
>Well, the subject line says it all. How do I `new' an object
>that's got a constructor? I am interested in `new'ing an array
>of such objects.

	Unfortunately, you can't 'new' an array of objects unless the
class has a default constructor.  This means that you can't pass an
initializer to a new stmt for an array.  The default constructor is called
for each element of the array (in ascending order).

	So, your "A *p2 = new A[10];" would work if you added a default
constructor to A.  Of course, you'd then have to set up each element,
and to do that you'd need some sort of A::SetValues() member function.
Not too nice.

	To initialize the elements in the declaration, rather than

>   A *p2 = new A(3)[10];

you can try:

    A p2[10] = { 3, 3, 3, 3, 3, 3, 3, 3, 3, 3 };

	Of course this isn't dynamic.  If you want a dynamically-allocated
array of A and you want to pass a value to the constructor, do the following:

    A **p = new A* [ ArraySize ];
    for ( int i = 0; i < ArraySize; ++i ) {
      p[i] = new A( InitialValue );
    }

Here each p[i] is a pointer to A, where each p2[i] above is an actual
object A.
-- 
Jonathan Fischer	     SCO Canada, Inc.	    Toronto, Ontario, Canada

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