Re: initializing a member pointer

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 29 Nov 2007 03:14:52 -0800 (PST)

Message-ID:

<358dcddf-b0e5-46e6-93be-89e2ecc438bf@j44g2000hsj.googlegroups.com>

On Nov 28, 5:57 pm, David Harmon <sou...@netcom.com> wrote:

On Wed, 28 Nov 2007 03:44:32 -0800 (PST) in comp.lang.c++,
maj...@majsta.net wrote,

   // this constuctor does not work
   C(int ii) {
           int *pI = new int(ii);
   }

As others have written, it is completely wrong to declare a local
variable here that is named the same as your member variable.

No one said that it was completely wrong. It's generally
considered bad style, because it is confusing to the reader, but
it is legal. In the case of constructors, in fact, it's not
that exceptional to give the argument (which also acts as a
local variable) the same name as the member.

But it's still wrong to use assignment instead of construction to
build member variables. Not that there is much difference in the
case of ints, but what you have should still be written as:

C(int ii) : pI(new int(ii)) {
}

Then next question would be WHY are you creating memory management
headaches for yourself by using 'new' at all here. I suppose this
is only a simplified example from your actual application, but
chances are you are still making trouble for no reason. Never use
'new' unless you have explored the alternatives and nothing easier
will do the job.

It's not always that simple. The usual reason for dynamic
allocation in such cases is polymorphism. And it's not always
possible to determine the desired actual type with a single
expression.

(In such cases, it's certainly worth considering using something
like boost::scoped_ptr for the member. If there's more than one
such pointer, you must consider some sort of special pointer
management.)

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