NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/15198

Text File | 1996-08-05 | 1.9 KB | 58 lines

Path: news.primenet.com!jstern
From: [e-mail] (Josh Stern)
Newsgroups: comp.lang.c++
Subject: Re: How to initialize array of objects using non-void constructor?
Date: 3 Apr 1996 21:57:02 -0700
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Steve Kettle <[e-mail]> wrote:
>Erik Max Francis  <[e-mail]> wrote:
>>Brian Leach wrote:
>>> Liang Lu wrote:

>>> Sorry Liang, it is not possible. The language does not allow for
>>> non-default
>>> constructors for arrays of objects.

The language basically provides the placement form
of operator new for this purpose (see below).

>>Nonsense; see Ellis & Stroustrup, 12.6.1.  Using non-default constructors for
>>initializing an array is much the same as one would expect (using the example
>>above):
>>
>>    Table object[3] = { object(1), object(1), object(2) };

>But you can't for an array on the heap.

Yes you can, it goes like this:

#include <new.h> // for placement new

Table* tptr = malloc(sizeof(Table)*num_tables);
if (!tptr) exit(1); // malloc failed
for (int i=0; i < num_tables; i++)
   new (tptr++) Table(val); // example for single arg constructor
                            // arbitrary number of args possible

There is also a do-nothing placement form of delete
that simply calls the destructor for the objects.
For convenience, check out the templates Construct
and Destroy in the file defalloc.h of the HP implementation
of STL.


- Josh



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