Question

I have a list of pointers to classes:

list<AbsClient*> clients;

AbsClient could be 1 of 3: TempClient , RegisteredClient , VIPClient.

Inside AbsClient there’s a protected variable: phone_number.

I need to iterate through the clients list, and search for a specific phone number.

I tried this:

    list<AbsClient*>::iterator iter;
    for(iter=clients.begin();iter!=clients.end();++iter)
{
    if(iter->phone_number == phone)
    {

    }
}

But it doesn’t give me access to the iter->phone_number:

error: expression must have pointer-to-class type

What’s wrong with this line?

P.S is it possible to use the stl::find function and somehow tell it to search by the “phone_number” variable?

Thank you

Answer 1

You can think of an iterator as a “pointer to an element” of your container. And the type of an element in your container is a AbsClient*—another pointer. So, at least syntactically, you’re in a double-pointer situation, so you need to change how you dereference your iterator:

(*iter)->phone_number == phone

Your post says that phone_number is a protected member, though, and you can’t access protected variables when you’re not inside that class or a derived class, so you either need to use an accessor method or change the visibility of your data member.

And no, you can’t use std::find to do this (at least not directly), but you can use std::find_if:

iter = std::find_if(clients.begin(), clients.end(),
    [phone](AbsClient* cl) { return cl->phone_number == phone; });

If you aren’t using C++11, then it’s a bit more verbose:

struct MatchPhone {
    explicit MatchPhone(PhoneNumber p) : phone(p) {}
    bool operator()(AbsClient* cl) {
        return cl->phone_number == phone;
    }
    PhoneNumber phone;
};

// ...
iter = std::find_if(clients.begin(), clients.end(), MatchPhone(phone));
// ...