Assignment operator isn't being called

[Chemical Engineer]

"Copying" never appears. Why?

struct Junk{
    int x;
    Junk *Junk::operator= (const Junk *inc){
        this->x = inc->x;
        cout << "Copying\n";
        return this;
    }
};

void main(){
    Junk *a = new Junk, *b;

    a->x = 5;
    b = a;  //should be using the assignment operator?

    cin.ignore();
    return;
}

I'm assigning a Junk pointer to another Junk pointer, which is what my assignment operator defines, right?

[Galik]

The assignment operator is only defined for type Junk. You are attempting to use in on a Junk*, because b is a Junk* and not a Junk.

[Chemical Engineer]

Junk *Junk::operator= (const Junk *inc){
is the same thing as
Junk* Junk::operator= (const Junk* inc){,
right?

If not, how could I change this to make it work for the Junk pointers?

PS- Actually, I'm just frustrated and confused. Any working example that you could give me would be nice right now.

[Galik]

I don't think you can make it work for Junk pointers. I am not really sure why you would want to either.

[Chemical Engineer]

So we can't use overloaded operators on objects referred to by pointers?

I was really fond of the abstraction that pointers afforded. It'd be a great shame if they have that limitation.

[Galik]

Maybe this will be helpful:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

#include <iostream> struct Junk { int x; Junk& operator=(const Junk& rhs) { x = rhs.x; std::cout << "Copying\n"; return *this; } }; int main() { Junk* a = new Junk; Junk* b = new Junk; a->x = 5; *b = *a; // This will call the assignment op std::cout << b->x << '\n'; std::cin.ignore(); }

Copying 5

[guestgulkan]

The whole point of the assignment operator is to assign the values of one
object to another.

using it on pointers to objects the way you doing is meaningless (and won't work) - pointers are all about addreses.

In your example above - what you would do is:

void main(){
    Junk *a = new Junk, *b;

    a->x = 5;
    b = new Junk (a);  //Create  a new object using an existing one - You need a Copy Constructor

    cin.ignore();
    return;
}

To assign an existing object to an already existing one - You use an assignment operator of the form - Note the use of the reference operator (NOT pointer operator)

struct Junk{
    int x;
    Junk &   operator= (const Junk& inc){
       //But remember to guard against self-assignment
        this->x = inc->x;
        cout << "Copying\n";
        return *this;
    }
};

So you can now say:

Junk a, b;  //Create some objects 
.....//manipulate the objects
a = b;  //assign one existing object to another 

[Galik]

Chemical Engineer wrote:

So we can't use overloaded operators on objects referred to by pointers?

You just need to dereference the pointer first using *: *ptr1 = *ptr2. That tells the compiler that it is the contents of the pointer that need assigning rather than the pointer itself.

Chemical Engineer wrote:

I was really fond of the abstraction that pointers afforded. It'd be a great shame if they have that limitation.

I avoid pointers like the plague. Sometimes they are necessary. But I would always go for a non-pointer solution given the choice.

[Chemical Engineer]

Thanks. I think that, after reading over that and playing around a bit, I should be able to get it.

Out of curiousity, why would you avoid pointers?

[Galik]

You have to manage the pointers yourself. That increases the possibility of errors. There is often no guarantee that they actually point to anything in a given piece of code.

[Galik]

Here is an example of some of the problems that pointers carry:

http://www.cplusplus.com/forum/beginner/27165/