Operator Overloading

[ace_of_pentacles]

Hi there,

I'm trying to write a smart pointer class for an int variable but I've gotten a little stuck. Firstly, to declare a smart pointer to an int, I MUST use this line of code (As seen in the main method below):

smart_pointer s = new int();

To do this, I try to overload the "=" operator and set a pointer to an int (called "value" in the smart_pointer class) to the address of this new int. However, I get this error:

"conversion from ‘int*’ to non-scalar type ‘smart_pointer’ requested"

What am I doing wrong? I thought "new int()" returned a memory address which I could set the smart_pointer's int pointer to by overloading the "=" sign...

Thank you.

-------Code-------

#include<stdio.h>
#include<stdlib.h>

class smart_pointer{
private:
int *value;

public:
smart_pointer();

// Overwrite "=" operator.
smart_pointer &operator=(int *val){
value = val;
return *this;
}

~smart_pointer(){
delete value;
}
};

smart_pointer::smart_pointer(){
value = NULL;
}

int main(void){
smart_pointer s = new int();
return 0;
}

[laserlight]

To do this, I try to overload the "=" operator

You are mistaken. This:

smart_pointer s = new int();

is equivalent to:

smart_pointer s(new int());

i.e., you should write a constructor instead (or perhaps, in addition to overloading operator= since you should also define or disable the copy constructor and copy assignment operator)

[monarch_dodra]

Looking at your implementation, you might be interested in just using auto_ptr instead.

If you have access to boost or C++0x, then you could look into unique_ptr and shared_ptr.

[ace_of_pentacles]

Ah, I see. Of course, the constructor would have to be the first thing to be called.
I feel a little silly now.

Thank you for taking the time to help me out.

[monarch_dodra]

[EDIT] Double post

[monarch_dodra]

Remember to make the constructor explicit. Inadvertently placing a pointer into an object that claims ownership of the pointer's life is one of the last things you want to do.

[EDIT]Whilst were on the subject, having "smart_pointer &operator=(int *val)" and being able to write "smart_pointer s = new int();" are both very bad ideas, for the same reason.

You'll want a named member function to do that.

PS: There is a flaw in your operator= implementation: What if your smart_pointer already had a value?