Mastering C++: A Comprehensive Quiz Based on 'Thinking in C++'

When should a copy constructor be explicitly defined by the programmer?

1. When the class does not contain any pointer members

2. Never, as the compiler provides a default

3. When the class requires a deep copy mechanism

4. Only for classes intended for inheritance

The correct answer is: When the class requires a deep copy mechanism

A copy constructor is used to create a new object as a copy of an existing object. Typically, the compiler provides a default copy constructor that simply copies all the members of the class. However, if the class contains pointer members, then a shallow copy is performed by the default copy constructor, which can lead to errors and memory leaks. In such cases, the programmer needs to explicitly define a copy constructor to perform a deep copy, which copies the values of the pointer members as well. Option A is incorrect because the class can still have other non-pointer members that need to be properly copied. Option B is incorrect because although the compiler provides a default, it may not be suitable for all cases, particularly when dealing with pointer members. Option D is incorrect because copy constructors are not only used for classes intended for inheritance, but for any class that needs proper copying of its members.