Question

What is a default copy constructor?

Short answer

A copy constructor is a special type of constructor used to create a new object as a copy of an existing one. The default copy constructor is a constructor provided implicitly by the compiler if the programmer does not specify a custom copy constructor. It performs a shallow copy of the source object's member variables to the new object, which can lead to potential issues with shared memory locations. To prevent this, a custom copy constructor can be defined to perform a deep copy, creating new memory locations for pointers and references.

Step-by-step solution

Define Copy Constructor

A copy constructor is a special type of constructor in object-oriented programming languages, such as C++ and Java. It is used to create a new object as a copy of an existing one. The copy constructor initializes the member variables of the new object from the corresponding variables of the source object. Step 2:

Explain Default Copy Constructor

A default copy constructor is a constructor provided implicitly by the compiler if the programmer does not specify a custom copy constructor. When invoked, the default copy constructor performs a shallow copy of the source object's member variables to the new object. This means that the member variables in the new object receive the same values as those in the source object. If the source object contains pointers or references, the default copy constructor copies their addresses rather than creating new memory and making a deep copy. In some cases, this may lead to unintended behavior. Step 3:

Address Potential Issues

One potential issue with default copy constructors is the shallow copy behavior of pointers and references. If the source object and the newly created object share memory locations due to the use of pointers, changes made to one object may affect the other, unintentionally. To prevent this issue, a programmer can define their own custom copy constructor that performs a deep copy, creating new memory locations for pointers and references, minimizing the risk of unintended side effects. Step 4:

Provide an Example

For example, consider a simple class in C++: ``` class MyClass { int a; int *b; public: MyClass(int num1, int num2) { a = num1; b = new int(num2); } }; ``` In this case, if the programmer does not specify a custom copy constructor, the compiler provides a default copy constructor. When creating a new object as a copy of an existing one using the default copy constructor, the new object will receive the same values for `a` and will point to the same memory location as the source object's `*b`. To avoid potential issues, the programmer can create a custom copy constructor that performs a deep copy: ``` MyClass(const MyClass& source) { a = source.a; b = new int(*source.b); } ```