c++ how to get address of an object in a vector from iterator

Question

I have a vector vec that contains objects Order (not pointers to the objects)

Now I need to find a certain object in the container and manipulate it

for ( auto it = vec.begin(); it !=  vec.end(); ++it ) {

    Order *p_o = it; // ERROR HERE
    if ( p_o->id_ == id ) { p_o->size_ -= reduce_amount; }

}


error: C2440: 'initializing': cannot convert from 'std::_Vector_iterator<std::_Vector_val<std::_Simple_types<Order>>>' to 'Order *'

How can I get the the address of the object the iterator hold

I tried both

it.pointer
it.reference

but that yields

C:\CPP\Simulator\Venue\venue.cpp:88: error: C2274: 'function-style cast': illegal as right side of '.' operator

Answer 1

Iterators model pointers, but aren't necessarily pointers themselves. So just dereference it, and if you really need to point at the object, take the address of that:

auto& my_ref_to_the_object = *iter;
auto* my_ptr_to_the_object = &my_ref_to_the_object;

Your code doesn't seem like you need a real pointer to the object at all:

for (auto it = vec.begin(); it !=  vec.end(); ++it) {
    Order& p_o = *it;
    if (p_o.id_ == id) {
        p_o.size_ -= reduce_amount;
    }
}

Or even simpler:

for (Order& p_o : vec) {
    if (p_o.id_ == id) {
        p_o.size_ -= reduce_amount;
    }
}