Example of Struct inside Class.

Hi,
I have been trying to learn C++ and I don't know how to use a struct inside a class, when both the struct and the class have Constructors defined. I'd be grateful if someone can point out where I'm going wrong in the following example.

Thanks a lot.

Code:

---

struct Items{
            int qty;
            Items(int input){qty = input;}//constructor.
};

class Basket{
      private:
            Items InBasket;
      public:
            Basket(int inval);
            void GetStuff();
};

Basket::Basket(int inval){
      Items(inval);
}

void Basket::GetStuff(){
      cout<<"\nIn basket = "<<InBasket.qty;
}

int main(void){
      Basket B1(5);
      B1.GetStuff();
      return(EXIT_SUCCESS);
}

---

EDIT** This is what you want

Code:

---

#include <iostream>
using namespace std;

struct Items{
    int qty;
    Items(int qty):qty(qty){}
};

class Basket{
    Items *InBasket;
public:
    Basket(int inval):InBasket(new Items(inval)){}
    void GetStuff(){
        cout << endl << "Inbasket = " << InBasket->qty << endl;
    }
    ~Basket(){delete InBasket;}

};

int main(void){

    Basket B1(5);
    B1.GetStuff();

    return(0);
}

---

Quote:

---

Originally Posted by Syscal

EDIT** This is what you want

Code:

---

#include <iostream>
using namespace std;

struct Items{
    int qty;
    Items(int qty):qty(qty){}
};

class Basket{
    Items *InBasket;
public:
    Basket(int inval):InBasket(new Items(inval)){}
    void GetStuff(){
        cout << endl << "Inbasket = " << InBasket->qty << endl;
    }
    ~Basket(){delete InBasket;}

};

int main(void){

    Basket B1(5);
    B1.GetStuff();

    return(0);
}

---

---

Thanks ! this works like a charm. However I have a question, what does the ":" notation mean? I mean what does the second line in the struct declaration say? Is it just initializing the value of qty with the supplied value? Please let me know, thanks again.

More or less, that is the idea: in inheritance hierarchies and with const members, initialization lists are required. Your actual problem is solved through assignment also, if you wish to avoid constructs you haven't learned.

Code:

---

inBasket = inval;
// Actually calls Basket(int)

---

There is one particular case where assignment looks like this:

Code:

---

inBasket = Items(inval);
// The constructor is 'explicit' and must be called this way

---

Explicit constructors should be a class of constructors that always have one argument. By declaring a class constructor explicit you are saying that you can't call the constructor this way:

Code:

---

Items i = 5;

---

As a more important aside, note that Syscal has changed the member of Basket to be a pointer. While in this case there is little difference it would perhaps have been more instructive to stick to one example.

The new is absolutely unnecessary, actually.
Taking syscal's example, this should work:

Code:

---

#include <iostream>
using namespace std;

struct Items
{
    int qty;
    Items(int qty): qty(qty) {}
};

class Basket
{
    Items InBasket;
public:
    Basket(int inval): InBasket(inval) {}
    void GetStuff()
    {
        cout << endl << "Inbasket = " << InBasket.qty << endl;
    }
};

int main()
{
    Basket B1(5);
    B1.GetStuff();

    return 0;
}

---

Then you have to change:

InBasket->qty

to

InBasket.qty


Also, the ":" notation is an initialization list. http://www.cprogramming.com/tutorial...lists-c++.html

And yes, it just initializes a field. So take this for example:

some_ctor(int value):some_private_field(value){}

"some_private_field" gets initialized to "value".

Thanks a lot to all of you for the help provided.