Question

I want to create a vector of object A (aArray) and manipulate the value of aArray.a when I call the Heap constructor. Currently, the values of aArray.a remain unchanged. How can I do this properly?

Thank you for your help!

#include <vector>
#include <iostream>

struct A
{
  A(int av):a(av){}

    int a;
};

struct Heap
{

  Heap(std::vector<A> *hVal)
  {
      for (int i=0; i<hVal->size(); ++i) 
      {
        hVec.push_back(hVal->at(i));
      }
      std::cout << std::endl;

      for(int i=0; i<hVec.size(); ++i)
      {
        hVec[i].a*=2;
        std::cout << "hVec[i].a*=2  is " << hVec[i].a << "\n"; 
      }
  }

  std::vector<A> hVec;
};


int main()
{
  A a0(2), a1(4), a2(8);  
  std::vector<A> aArray;  
  aArray.push_back(a0);
  aArray.push_back(a1);
  aArray.push_back(a2); 

  Heap h(&aArray);

  for(int i=0; i<aArray.size(); ++i)
  {
    std::cout << "aArray[i].a = " << aArray[i].a << "\n";
  }

  return 0;

}

Answer 1

Your Heap constructor copies *hVal to hVec, then modifies hVec. If you want it to update aArray in main, modify *hVal instead (for example via hVal->at(i).a *= 2;).

Update:

struct Heap {
    Heap(std::vector<A> *p) : ptr(p) {}

    void multiply_by(int n) {
        for (int i = 0; i < ptr->size(); i++) {
            (*ptr)[i] *= n;
        }
    }

    std::vector<A> *ptr;
};

...

Heap h(&aArray);
h.multiply_by(2);