A question about 'Return Value'

I have the following code just for fun

Code:

---

class Base{
public:
        Base(){cout<<"Constructor"<<endl;}
        Base(const Base &obj){cout<<"Copy Constructor"<<endl;}
        Base & operator=(const Base& obj){
                cout<<"Operator="<<endl;
                return *this;
        }
};

Base foo(){
        Base x;
        return x;
}

void main(){
        Base tmp = foo();
}

---

=================
Why the outputs are only

Constructor
Copy Constructor

But I think the outputs should be:
Constructor
Copy Constructor // from return x
Copy Constructor // from Base tmp = foo();

tmp called the copy constructor automatically. Nah nah.

But I think the outputs should be:
Constructor
Copy Constructor // from return x
Copy Constructor // from Base tmp = foo();

Your compiler is probably optimizing out one of the copies.

This:

Code:

---

Base tmp = foo();

---

Is rearranged by the compiler to become:

Code:

---

Base tmp(foo());

---

So, the constructor is called in foo, and then this object is used (copy constructor called) to initialize tmp, so the output is as you've mentioned:
Constructor (from inside foo function)
Copy Constructor (initializing tmp from foo's return value)

And a compiler would be allowed to be even more aggressive and eliminate even the single copy being done.

Side note: void main() is evil. Use int main().

u have a mistake in the assignment operator, you should check if the passed object is the same one (memory address)

Code:

---

Base & operator=(const Base& obj){
              //Check if the object is being assigned to it self
              //By comparing the memory adress
              if(this == &obj) {return *this;}
                cout<<"Operator="<<endl;
                return *this;
        }

---

Quote:

---

Side note: void main() is evil. Use int main().

---

Exactly :D, Bjarne in his website wrote: It has never been "void" for neither C++ nor C

Quote:

---

Originally Posted by Hussain Hani

u have a mistake in the assignment operator, you should check if the passed object is the same one (memory address)

---

It's actually pretty wasteful to check for self assignment in cases where it is harmless, such as this case.

Quote:

---

Originally Posted by AverageSoftware

It's actually pretty wasteful to check for self assignment in cases where it is harmless, such as this case.

---

Indeed.
This is a good read on the subject of self-assignment:
http://www.gotw.ca/gotw/011.htm