Question

class a
{
  private:
    b *b_obj;
  public:
    void set(int);
};

a::a()
{
  b_obj = new b;
}

a::set(int s)
{
  b_obj->c = s;
 }

class b
{
  public:
    int c;
};

is this code valid?
if no, how do i make b_obj of a particular object (say a_obj) of class a ,modifiable in another class c…if a_obj i created in another class d….i am scared of a_obj going out of scope in class c.

hope you understand my question.
thanks a lot for taking the time to read my post

Answer 1

The code is nearly valid. class b needs to be declared (or at least forward declared) before it is referred to in class a, you do not specify the return type in the definition for a::set, and you have not provided a declaration for a‘a default constructor. Here is the revised code, along with a test harness:

class b
{
  public:
    int c;
};

class a
{
  private:
    b *b_obj;
  public:
    a();
    void set(int);
};

a::a()
{
  b_obj = new b;
}

void a::set(int s)
{
  b_obj->c = s;
}

int main()
{
    a my_a;
    my_a.set(42);
}

Now, just because the code is valid doesn’t mean it’s good:

1. You don’t initialize c when default-constructing b.
2. You use raw pointers to dyanamically-allocated b‘s. Use automatic variables instead, whenever possible. Among the the reasons for this are …
3. You never delete the b you new‘ed in a‘a constructor. This results in a memory leak. If you had avoided the use of dynamic allocation in the first place, this would not be an issue.