how to dereference a pointer of an object inside another object

Question

I need to build a set of classes that are dependent on each other. I am having trouble when I pass a pointer to one class to another class that is instantiated inside it.

Here an example to illustrate my problem.

#include<iostream>
#include<vector>

using namespace std;

class base;

//

 child class
    class child
    {
    public:
    child(){};
    void setPointer (base* ptr){pointer = ptr; }
    void printing(){(*pointer).print();} // error C2027: use of undefubed type base
                                        // error C2227: '.print' must have class/struct/union
private:
    base* pointer;
};

// base class
class base
{
public:
    base()
    {
        initial_vec();
        VEC[0].setPointer(this);
        VEC[0].printing();
    }

    void print() { cout <<"printing from BASE"<< endl;}

    void initial_vec ()
    {
        child child1;
        VEC.push_back(child1);
    }

private:
    vector<child> VEC;
};

int main()
{
    base b1;

    system("pause");
    return 1;
}

Do you have any idea how I achieve that without getting those errors ?

Thank you in advance

You cannot dereference a forward declaration from inlined code. This must be externed to a separate translation unit. — πάντα ῥεῖ, Apr 06 '15 at 14:41

score 0 · Answer 1 · edited May 23 '17 at 11:50

0

It looks like the error you are getting it because you are trying to call printing() from your base class with only a forward declaration. To fix your problem, define the body of the function printing() after your base class has been fully defined.

Here is more details on forward declaration.

edited May 23 '17 at 11:50

Community

1
1

answered Apr 06 '15 at 14:45

dwcanillas

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score 0 · Answer 2 · answered Apr 06 '15 at 14:47

"Do you have any idea how I achieve that without getting those errors ?"

It's fairly simple. You omit the inlined codeparts that reference base, and move tem after the full declaration of the class:

#include<iostream>
#include<vector>

using namespace std;

class base;

 child class {
    public:
    child(){};
    void setPointer (base* ptr); // <<< Only declare the functions here
    void printing();

private:
    base* pointer;
};

// base class
class base {
public:
    base()
    {
        initial_vec();
        VEC[0].setPointer(this);
        VEC[0].printing();
    }

    void print() { cout <<"printing from BASE"<< endl;}

    void initial_vec ()
    {
        child child1;
        VEC.push_back(child1);
    }

private:
    vector<child> VEC;
};

Define the functions after base was fully declared:

void child::setPointer (base* ptr){pointer = ptr; }
void child::printing(){(*pointer).print();}

int main() {
    base b1;

    system("pause");
    return 1;
}

how to dereference a pointer of an object inside another object

2 Answers2