C++ Objects: When should I use pointer or reference

Question

I can use an object as pointer to it, or its reference. I understand that the difference is that pointers have to be deleted manually, and references remain until they are o

Answer 1

Here's another answer (perhaps I should've edited the first one, but since it has a different focus, I thought it would be OK to have them separate).

When you create a pointer with new, the memory for it is reserved and it persists until you call delete on it - but the identifier's life span is still limited to the code block's end. If you create objects in a function and append them to an external list, the objects may remain safely in the memory after the function returns and you can still reference them without the identifier.

Here's a (simplified) example from Umbra, a C++ framework I'm developing. There's a list of modules (pointers to objects) stored in the engine. The engine can append an object to that list:

void UmbraEngine::addModule (UmbraModule * module) {
    modules.push(module);
    module->id = modules.size() - 1;
}

Retrieve one:

UmbraModule * UmbraEngine::getModule (int id) {
    for (UmbraModule **it=modules.begin(); it != modules.end(); it++) {
        if ((*it)->id == id) return *it;
    }
}

Now, I can add and get modules without ever knowing their identifiers:

int main() {
    UmbraEngine e;
    for (int i = 0; i < 10; i++) {
        e.addModule(new UmbraModule());
    }
    UmbraModule * m = e.getModule(5); //OK
    cout << m << endl; //"0x127f10" or whatever
    for (int j = 0; k < 10; j++) {
        UmbraModule mm; //not a pointer
        e.addModule(&mm);
    }
    m = e.getModule(15);
    cout << m << endl; //{null}
}

The modules list persists throughout the entire duration of the program, I don't need to care about the modules' life span if they're instantiated with new :). So that's basically it - with pointers, you can have long-lived objects that don't ever need an identifier (or a name, if you will) in order to reference them :).

Another nice, but very simple example is this:

void getVal (int * a) {
    *a = 10;
}
int main() {
    int b;
    getVal(&b);
    return b;
}