Deep Copy vs. Shallow Copy: When Do I Need to Clone the Data?

Deep Copy vs. Shallow Copy: A Closer Look

In object-oriented programming, understanding the difference between deep and shallow copies is crucial. Let's delve into the concepts to clarify the distinction.

Shallow Copy

A shallow copy creates a new object that references the same objects as the original object. This means that if one of the objects changes, it affects both the original and copied objects.

Consider the following example:

<code class="cpp">class X {
    private:
        int i;
        int *pi;
    public:
        X() : pi(new int) {}
        X(const X& copy) : i(copy.i), pi(copy.pi) {}
};</code>

In this scenario, the pi member points to the same integer in both the original and copied X objects.

Deep Copy

In contrast, a deep copy creates a new object and clones all the members of the original object. There are no shared objects between the original and copied objects.

Here's a modified example:

<code class="cpp">class X {
    private:
        int i;
        int *pi;
    public:
        X() : pi(new int) {}
        X(const X& copy) : i(copy.i), pi(new int(*copy.pi)) {}
};</code>

In this case, the pi member of the original and copied X objects points to different integer objects, but they both contain the same value.

Copy Constructor

When creating a copy of an object, a copy constructor is used. The default copy constructor (if not explicitly defined by the programmer) typically performs a shallow copy, except for members that have their own custom copy constructors.

However, it's important to note that the behavior of a copy constructor can vary depending on the specific data members it contains. Some members may perform deep copies, shallow copies, or a combination thereof.

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