Re: new operator for arrays

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Sun, 10 Aug 2008 22:55:04 +0200

Message-ID:

<-7ydnQ15fJOsyALVnZ2dnUVZ_jOdnZ2d@posted.comnet>

* Pawel_Iks:

Let's consider following class:

class A {
int sth;
public:
A(int s): sth(s) {}
A() {}

Note: here the 'sth' member is uninitialized, with indeterminate value.

Instead you can do e.g.

A(): std(0) {}

or merge that with your one-argument constructor by using a default,

A( int s = 0 ): sth( s ) {}

~A() {}
}

and when I'd like to create an array with 100 elements of A type I
write:

A* tab=new A[100]

but I'm interested if it is possible to use constructor A(int) instead
of A() with new operator, and if not why?

You can't, because that's a feature the core language does not support. However,
std::vector supports specification of a default value. E.g.,

std::vector<A> v( 100, A(42) );

In general, use the standard library container types, or e.g. Boost container
types, instead of using new and delete directly.

It's much safer, and much easier.

Cheers, & hth.,

- Alf

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?