Initializing Vector of Objects with NULL

class A; //forward defined in class B.h
class B
{
private:

vector<B> v1;
vector<B> v2[3];

public:
void Display()
{
cout<<v1[0].display()
}

}


I get error message forward Declaration of class A;

What is going on here. Is there a way I could initialize all the vectors of type B to be set to NULL in the constructor?

When posting code, please format the code properly first and use code tags. Go advanced, select the code and click '#'.

In the code snippet shown, class A is not used and class B has vectors of type class B? Please post the smallest complete program that shows the problem rather than just a small part.

Quote:

---

Originally Posted by 2kaud

When posting code, please format the code properly first and use code tags. Go advanced, select the code and click '#'.

In the code snippet shown, class A is not used and class B has vectors of type class B? Please post the smallest complete program that shows the problem rather than just a small part.

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I am new to this and not sure what exactly you mean.

Anyways, All I want is to create a vector of objects of a particular class. What is the difference between

vector<B> *v1
and
vector<B*> v1?

Okay here I go again:

I have:

Code:

---

#include "A.h"
class A; //Forward Declared
class B
{
vector <A> v1;
public:
  B(A &a)
  { ...
  }
 
  v1.push_back(obj);
  cout<<*v1[0].display();
};

---

I am getting an error of forward Declaration of 'class A'

What is the best way to resolve this problem.

Code:

---

vector<B> *v1;

---

v1 is a pointer to a vector of type B

Code:

---

vector<B*> v1;

---

v1 is a vector of type pointer to B

If class A is defined in A.h and is included before any reference to class A as in your code snipped, then the forward declaration of class A is not needed so just remove it.

Quote:

---

Originally Posted by 2kaud

Code:

---

vector<B> *v1;

---

v1 is a pointer to a vector of type B

Code:

---

vector<B*> v1;

---

v1 is a vector of type pointer to B

If class A is defined in A.h and is included before any reference to class A as in your code snipped, then the forward declaration of class A is not needed so just remove it.

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Thanks. However, I need this forward declaration because I have a class B using class A as well. It's like a cyclic relationship

Quote:

---

Originally Posted by apb210

Code:

---

#include "A.h"
class A; //Forward Declared
class B
{
vector <A> v1;  //<<<--need definition of A
public:
  B(A &a) // <<<--this will compile, but you can't do much with variable a since you don't have it's definition
              // you can only use a as an anonyous definition (you can take it's pointer that's about it).
  { ...
  }
 
  v1.push_back(obj);
  cout<<*v1[0].display();
};

---

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If you do forward defines:
you can ONLY declare pointers and references of forwarded classes/structs.