[FIXED] How to make pointer/reference on element in vector?

Issue

I have two vectors and for some elements (not all) i need them to be connected ~ if i delete/change this element in one vector it should be removed/changed in both.

Something similar like pointers:

int r = 10;
int *p= &r;
*p = 3;

For example in next code it should change myvector2[0].a to 7.

#include <iostream>
#include <vector>

using namespace std;

struct elt {
    int a, b, c;
};

int main()
{

    vector<elt> myvector;
    vector <elt> myvector2;
    elt elt1 = {1,3,3};

    myvector.push_back(elt1);
    elt *elt2 = &elt1;
    myvector2.push_back(*elt2);

    myvector[0].a=7;

    cout << myvector[0].a << endl; //7
    cout << myvector2[0].a << endl; //1

    return 0;
}

How can i make this possible? Please help!!!

Solution

As tgmath explained, the issue is that you wind up with two different objects in your vectors, as the standard containers store elements by value. I would recommend that you use shared pointers to properly maintain the lifetime of the objects (note this uses C++11 features):

#include <iostream>
#include <vector>
#include <memory>

struct elt {
    int a, b, c;
};

int main()
{
    std::vector<std::shared_ptr<elt>> myvector;
    std::vector<std::shared_ptr<elt>> myvector2;
    auto elt1 = std::make_shared<elt>(elt {1,3,3});

    myvector.push_back(elt1);
    myvector2.push_back(elt1);

    myvector[0]->a=7;

    std::cout << myvector[0]->a << std::endl; //7
    std::cout << myvector2[0]->a << std::endl; //7

    return 0;
}

Answered By - Dark Falcon

Answer Checked By - Pedro (PHPFixing Volunteer)