Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!tdatirv!sarima
From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: comp.lang.c++
Subject: Re: Initializing a Member That is a Class
Message-ID: <125@tdatirv.UUCP>
Date: 4 Feb 91 15:55:57 GMT
References: <1991Jan31.194631.3447@persoft.com>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Distribution: na
Organization: Teradata Corp., Irvine
Lines: 36

In article <1991Jan31.194631.3447@persoft.com> eda@persoft.com (Ed Almasy) writes:
>Assuming:
>    A is a class, with a constructor that requires 3 arguments
>    B is a class, containing a member of type A
>    C is a struct, containing a member of type A
 
>My question is:  When I create data items of type B or C, where do the
>constructor arguments for the member that is of type A come from?

Hmm, I rather though the explanation of this in Lippman was quite clear.
Essentially you pass arguments to the A constructor from the B and C
constructors.  The arguments can, of course, be any legal C++ expression
involving identifiers that are in scope at the time.  This includes the
arguments to the B/C constructors.

The syntax is as follows:

class B
{
	A a_member;
    public:
	B(...) :a_member(d, e, f) {.... };
}

For instance any of the following would bbe legal:
	B::B(z) :a_member(1, 2, 3) {...}
	B::B(z) :a_member(z, z, z+3) {...}
	B::B(y, z) :a_member(5, y+z, y) {...}
and so on.  The rules are exactly the same for struct C (because a struct
is just a special case of a class).  
(Note that the sub-constructor arguments go with the *definition* of the
outer constructor, not with its declaration in the class definition when
the two are different).
-- 
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uunet!tdatirv!sarima				(Stanley Friesen)