not declared in this scope c++

Question

I am in the middle of a c++ project and I get the well-known error "not declared in this scope". Specifically "vexp was not declared in this scope". As you can see below, vexp is a vector declared in class Exploration and although I have included Exploration.h in main, vexp is not reachable. On the other hand Exploration::vexp is not acceptable because vexp is not static. Is making vexp static the only way to access it from main???

#include "exploration.h"
#include <iostream>
#include <vector>

int main()
{

    std::srand (time(NULL));

    for(int i=1; i<9; i++)
    {
        Exploration temp (0,3,3);
        vexp.push_back(temp);
    }
    for(int j=0; j<(int)Exploration::vexp.size(); j++)
    {
        std::cout << Exploration::vexp[j].Vertical;
        std::cout << Exploration::vexp[j].Horizontal;
        std::cout << Exploration::vexp[j].r;
        std::cout << '\n';
    }

    return 0;
}

And the header:

#ifndef EXPLORATION_H
#define EXPLORATION_H
#include<vehicle.h>
#include <vector>

class Exploration : public vehicle
{
    public:
    std::vector <Exploration> vexp;
    Exploration(bool,float,int);
    int r;
    void DangerCheck();
    bool expaxis(int k);
};
#endif // EXPLORATION_H

Answer 1

vexp is a non-static member of Exploration. Each Exploration object you create will have its own vexp member. So to access a vexp, you need to have an Exploration object. That is, the following would work:

Exploration exp1(false, 3.0f, 5);
Exploration exp2(true,  6.0f, 10);
exp1.vexp.push_back(exp2);

Note that I'm accessing the vexp member of exp1 with exp1.vexp. That is the vector that belongs to that particular Exploration object. To that vector I am pushing exp2.

What exactly you need to do depends on what you're trying to do, and that I am not sure of. It seems that you don't fully grasp object-oriented principles. It should be clear to you that because vexp is a non-static member of Exploration, it doesn't exist until you create an Exploration object. That is, each Exploration object owns a container of more Exploration objects.

It looks as though maybe you just want a std::vector<Exploration> that is not a member of Exploration. So you just want a container of Explorations, not owned by other Explorations. For that, you would just do:

int main()
{
  std::srand (time(NULL));
  std::vector<Exploration> vexp; // vexp has been moved here

  for(int i=1; i<9; i++)
  {
      Exploration temp (0,3,3);
      vexp.push_back(temp);
  }
  for(int j=0; j < vexp.size(); j++)
  {
      std::cout << vexp[j].Vertical;
      std::cout << vexp[j].Horizontal;
      std::cout << vexp[j].r;
      std::cout << '\n';
  }
}

Note that vexp is now declared local to the main function and should be removed from the Exploration class.

Answer 2

You have to access vexp as member of Exploration object if you don't want to make it static ex.

temp.vexp.push_back(something);

But it doesn't seem like you want that. In your case it seems like you should make it static or a global variable.

Answer 3

vexp is member variable of class Exploration so it should be used with instance of class Exploration

temp.vexp.push_back(SomeVariable);

But, it is not recomended to declare your member variable as public and use it like this outside class.

Answer 4

Is vexp meant to be a list of all your Explorations? If so you need to declare it outside of the Exploration class. You can then do your

Exploration temp (0,3,3);
vexp.push_back(temp);

and it should work fine.

If on the other hand it's meant to be a vector attached to a specific Exploration, then this section is very confusing:

  Exploration temp (0,3,3);
  vexp.push_back(temp);

You would need instead something like

  Exploration myExpl;
  for(int i=1; i<9; i++)
  {
      Exploration temp (0,3,3);
      myExpl.vexp.push_back(temp);
  }

Answer 5

Take the vexp out of the class:

 std::vector<Exploration> vexp;

and:

 for(int j=0; j<vexp.size(); j++)
 {
     std::cout << vexp[j].Vertical;
     std::cout << vexp[j].Horizontal;
     std::cout << vexp[j].r;
     std::cout << '\n';
 }