Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!oberon!nunki.usc.edu!jeenglis
From: jeenglis@nunki.usc.edu (Joe English)
Newsgroups: comp.lang.c++
Subject: Re: Initializer in C++
Keywords: constructor, operator=
Message-ID: <2615@nunki.usc.edu>
Date: 7 Feb 89 00:30:39 GMT
References: <668@usl.usl.edu>
Reply-To: jeenglis@nunki.usc.edu (Joe English)
Organization: University of Southern California, Los Angeles, CA
Lines: 50


pcb@usl.usl.edu (Peter C. Bahrs) writes:
>In standard C we have the ability to initialize arrays such as:
>  
>   int x[] = {1,2,3};
>and
>   static int x[2][3] = {{1,2,3},{4,5,6}};
>etc...
>
>I would like to have a class such as ARRAY (actually matrix) that
>takes initializers...
>   ARRAY x(2,3)={{1,2,3},{4,5,6}};
>
>So the construct would?? be someting like:
>   ARRAY (int r, int c)
>   {
>      allocate the buf to be r by c...
>   }
>And now I guess the operator= would be:
>   void operator=(int *s)
>    {
>     now loop through and let each buf[i][j] = *s
>      and then s++
>    }
>This is as close as I have come, however it doesn't work, the operator=
>never gets called.  Maybe the constructor should take another parameter???

operator= is only called when an assignment is made to an
*already initialized* object.  In the case of an initializer
like "SomeClass Foo = Bar;" what gets called is
SomeClass::Someclass(typeof(Bar)), if it exists.  I'm not sure
if your example is legal -- can you use both initializer forms
in the same statement, like "SomeClass Foo(diddle,wubba) = Bar;" ?

You're right, you need to add another parameter to the
constructor, to take the values of the array.  However, you
can't write ARRAY x(2,3,{{...},{...}}); since it's not
possible to declare aggregate or array constants other than
strings (I think**).  You'll still have to declare a static
int[][] to hold the values (since this can take an aggregate 
initializer) and pass it to the constructor.

(**Or is it possible in C++ yet?  If so, I haven't heard about it.
 The lack of support for aggregate constants is being discussed in 
 comp.lang.c right now.)


--Joe English

  jeenglis@nunki.usc.edu