Problem passing a list of objects to another class, C++.

Question

Below I have written a sample program that I have written to learn about passing a list of objects to another class. I talk about the problems I am having below.

#include <iostream>
#include <vector>
using namespace std;

class Integer_Class
{
 int var;
public:
 Integer_Class(const int& varin) : var(varin) {}
 int get_var() { return var; }
};

class Contains_List
{
 typedef Integer_Class* Integer_Class_Star;
 Integer_Class_Star list;
public:
 Contains_List(const Integer_Class_Star& listin) : list(listin) {}
 Integer_Class* get_list() { return list; }
};

int main (int argc, char * const argv[])
{
 // Create a vector to contain a list of integers.
 vector<Integer_Class> list;
 for(int i = 0; i < 10; i++)
 {
  Integer_Class temp_int(i);
  list.push_back(temp_int);
 }

This is where the errors start occuring. Could someone please look at the second class definition and the code below and shed some light on what I'm doing wrong. Thank you so much, as always!

 // Import this list as an object into another object.
 Contains_List final(list);

 // Output the elements of the list by accessing it through the secondary object.
 for(int i = 0; i < 10; i++)
 {
  cout << final.get_list()[i].get_var();
 }

 return 0;
}

Answer 1

You don't mention what sort of errors you are getting, but one very obvious problem with your code is that the constructor for Contains_List expects a pointer to Integer_Class while the parameter you are sending it (list) is of type vector<Integer_Class>.

A vector is not the same as an array, so you cannot pass it as pointer to the type it contains. Either change your constructor to accept a vector or pointer/reference to vector, or change the code that is causing you problems so that it sends it a pointer to an array.

Answer 2

The 'Contains_List' constructor takes in an 'Integer_Class*'

You declare 'list' to be of type 'vector', yet you pass it to the the 'Contians_List' constructor. You should change the 'Contains_List' class so that it holds a vector instead of an Integer_List array. The two are not interchangeable.

You could also change the vector to be an array of Integer_List's instead, if you so wished.