[stayscrisp]

Hey Time for week 6 of the interview questions.

Question 1

a.) Explain the difference between a copy constructor and an overloaded assignment operator?

b.) What happens if you declare the only constructor in a class as private? Give an example of why you might want to do this.

Question 2

What was the last game you played and what did you think of it?

Please use spoiler tags for answers

This post has been edited by stayscrisp: 21 March 2011 - 06:39 AM

[sh1n3]

Question 1:

Spoiler

a) Copy constructor is a constructor that shares the reference location of an already existing constructor. While I think overloading assignment operator also has something to do with copying but refers to a separate memory allocation.

Objects cannot be created of that class. It would be used when one would want to have only one instance of that class. Eg: Many programs give the error " * can run only one instance at a time. "

Question 2:Last game I played was Assassin's Creed 2, it was amazing and had great Graphics, AI and good Music.

Is this right? I think the first one is wrong.

This post has been edited by stayscrisp: 21 March 2011 - 06:39 AM
Reason for edit:: Added spoiler tags :)

[anonymouscodder]

You can also use private constructors to let only specific classes or functions to instantiate the class (by declaring they as friend).

[hype261]

Here are my answers.

Spoiler

A copy constructor is called when a new object is created. An assignment operator is called when the object already exists.

class Foo
{
public:
Foo(){};
Foo(const Foo &){};
Foo & operator=(const Foo &){};

};

void someMethod()
{
Foo f; //calls Constructor
Foo g = f; //calls Copy Constructor.  G is a new variable being created
Foo h; //calls Constructor
h = f; //calls assignment operator.
}

If you declar the only constructor of an class private it means that the programmer can't create an object of that class the regular way. This is useful in many circumstances. If your object only contains static method then you wouldn't want somebody to create an object that isn't required. Also declaring the constructor private it useful if you are planning to use a Factory or a Builder to control initialization of the class. You would declare the Factory as a friend of the class so that it could call the private constructor.

This post has been edited by hype261: 21 March 2011 - 07:08 AM

[shintetsu_80]

Question 1:

Spoiler

a) The copy constructor instantiates a new of object with the same state as the object being copied. The assignment operator assigns an objects state to and already existing object.
With the copy constructor there is no pre-existing state to worry about, but with the assignment operator the current state of the object being assigned to may be of concern.

b) By declaring the only constructor as private you are limiting it's instantiation. This is something you would want to do if you creating a Singleton as we discussed in week 4.

Question 2:

Spoiler

2) The last game I played was Rift. It's a good game but I seem to notice input response problems. Mostly in terms of latency issues but patches are coming in quickly and the problem is getting better.

This post has been edited by shintetsu_80: 21 March 2011 - 07:23 AM

[NeoTifa]

How fun.

Spoiler

1.a) I remember only really going over this a little bit in class, but I'll give it a try. A copy constructor is a constructor that takes and instance of the same class and reassigns the class values with the one assigned so you're not left with any memory leaks. An overloaded operator assignment is where you redefine the behavior of a specific operator. In this comparison, you would overload = and in it you would call the copy constructor, since it's reassigning values.

1.B) I think I remember something like this too when we were briefly discussing design patterns. You would do this to make sure there ever only one instance of the class. This is for utility objects, kinda like Java's Math I think.

2.) The Last game I played was L4D2. I like the game a lot. There isn't much of a storyline, but it's a FPS with a purpose, so to say. The character dialog is amusing, the graphics are fantastic, and the levels are challenging enough to not bore me, but doable so I don't get frustrated and "rage quit".

This post has been edited by NeoTifa: 22 March 2011 - 01:34 PM

[stayscrisp]

Wkikipedia has a great example of why you sometimes need a user defined copy constructor, what happens when you run this code?

#include <iostream>
 
class Array {
public:
    int size;
    int* data;
 
    explicit Array (int size)
        : size (size), data (new int[size]) {}
 
    ~Array() 
    {
        delete[] data;
    }
};
 
int main()
{
    Array first (20);
    first.data[0] = 25;
 
    {
        Array copy = first;
 
        std::cout << first.data[0] << " " << copy.data[0] << std::endl;
 
    }    // (1)
 
    first.data[0] = 10;    // (2)
 
    return 0;
}

[hype261]

stayscrisp, on 29 March 2011 - 05:28 PM, said:

Wkikipedia has a great example of why you sometimes need a user defined copy constructor, what happens when you run this code?

#include <iostream>
 
class Array {
public:
    int size;
    int* data;
 
    explicit Array (int size)
        : size (size), data (new int[size]) {}
 
    ~Array() 
    {
        delete[] data;
    }
};
 
int main()
{
    Array first (20);
    first.data[0] = 25;
 
    {
        Array copy = first;
 
        std::cout << first.data[0] << " " << copy.data[0] << std::endl;
 
    }    // (1)
 
    first.data[0] = 10;    // (2)
 
    return 0;
}

(1) Array copy is going to go out of scope and call its destructor. Since copy used the copy constructor to build itself and the compiler provided the copy constructor a shallow copy of data was perform. The destructor of copy will delete data, but sadly Array first will still be pointing to the same data.

(2) This is a dangling pointer issue. The program is assigning a value to memory which it doesn't own anymore. The program could work correctly, could crash, could cause OS to crash, or could cause Computer to grow legs and light itself on fire. Anything is possible.

[Peabsesora]

You have missed the most important.

[hype261]

Peabsesora, on 03 April 2011 - 04:43 PM, said:

You have missed the most important.

Are you talking about the fact that the program is going to crash when the second Array goes out of scope?? I didn't miss that. I thought we were only supposed to comment on the numbered items. If that wasn't what you meant then please inform me what I missed.