Re: pointer in queue

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 2 Feb 2009 01:26:16 -0800 (PST)

Message-ID:

<6ea95c2f-b198-4f01-8247-223b0a561202@q30g2000prq.googlegroups.com>

On Feb 2, 10:07 am, Kai-Uwe Bux <jkherci...@gmx.net> wrote:

Ian Collins wrote:

Carl Forsman wrote:

I have a deque object.

Can I insert pointers into the queue? (I heard I cannot
insert pointer into a queue)

like this:
===============
std::deque < Sock* > * socks;
socks = new deque< Sock* >;

Why use new here?

int port = 4322;

for ( int i = 0; i< 10; i++ ) {
Sock * sock = new Sock();
sock->Create1(this, port);
socks->push_back(sock);
}

later I will loop the queue of socket:
===============
for ( std::deque<Sock>::const_iterator iter = socks->begin(); iter !=

socks->end(); iter++ ) {

for ( std::deque<Sock*>::const_iterator iter = socks->begin();
iter != socks->end(); ++iter ) {

Sock temp = iter->first; // get the 1st socket

A deque iterator does not have a member first.

Unless you want to copy the object, you would require:

const Sock& temp = **iter;

Note the use of const reference. *iter is a Sock*.

Just a nit: the const is optional and might cause trouble.

What sort of trouble?

The queue contains Sock* not Sock const *. The use of a
const_iterator only implies that the Sock* inside the queue
cannot be cahnged, but that doesn't make the pointee const
Sock. So,

Sock & temp = **temp;

is possible too would work when inside the loop non-const
methods of Sock are called.

The correct handling of const might be an argument for not using
pointers. IMHO, the real question here isn't whether you can
have a deque< Sock* > (obviously you can), but whether you want
to. If Sock has identity, or if the container contains
polymorphic objects, you need to use the pointer version, but
otherwise, I'd stick with putting the objects themselves in the
container.

--
James Kanze (GABI Software) email:james.kanze@gmail.com
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