Chapter 11: Problem 22

Explain why a class's copy constructor is called when an object of that class is passed by value into a function.

Short Answer

Expert verified

A copy constructor is a special constructor that creates a new object based on an existing object's values, ensuring a deep copy rather than a shallow copy. It is called when an object is passed by value to a function to create a temporary object, which maintains the integrity of the original object and prevents unintended changes. The copy constructor's primary function is to allow the program to work with a copied object within the function without modifying the original object's data and resources.

Step by step solution

What is a copy constructor?

A copy constructor is a special constructor in a class that is called when an object is initialized with the same class's previously-created object. Its purpose is to create a new object that is a copy of an existing object. The syntax of a copy constructor is: ``` ClassName( const ClassName &obj ); ``` Where `ClassName` is the name of the class, and `obj` is the object being passed to the copy constructor as a reference.

Passing objects by value

When an object is passed by value to a function, that means a new local object is created with the same values as the original object. In order for this new object to be a true copy of the original, the class needs a copy constructor to ensure that the new object is constructed correctly, and to avoid the shallow copy of the original object.

Why is the copy constructor called?

The copy constructor is called in the following situations: 1. When an object is initialized with another object's values (explicitly or implicitly). 2. When an object is passed by value to a function. 3. When an object is returned by value from a function. In this case, we are focusing on point 2, when an object is passed by value into a function. The copy constructor is called to ensure that all data members and resources of the original object are properly duplicated for the new, temporary object being created within the function.

Benefits of a copy constructor

The copy constructor helps maintain the integrity of the original object in the following ways: 1. It ensures a deep copy is made, copying the values of the original object, and not just referencing the same memory locations. 2. It prevents unintended changes to the original object or its resources within the function because the function works with a copy, not the original object.

Example

Here's a simple example to demonstrate the concept: ```cpp #include using namespace std; class MyClass { int num; public: MyClass() {} MyClass(int a) { num = a; } MyClass(const MyClass &obj) { num = obj.num; } int getNum() { return num; } }; void someFunction(MyClass obj) { obj = 25; } int main() { MyClass originalObj(10); someFunction(originalObj); cout << "Value of originalObj is: " << originalObj.getNum() << endl; } ``` Output: ``` Value of originalObj is: 10 ``` If the copy constructor were not called when passing `originalObj` to `someFunction`, then the value of `originalObj` would have been modified inside `someFunction`. However, since the copy constructor is called, the value of `originalObj` remains unchanged.

Unlock Step-by-Step Solutions & Ace Your Exams!

Full Textbook Solutions
Get detailed explanations and key concepts
Unlimited Al creation
Al flashcards, explanations, exams and more...
Ads-free access
To over 500 millions flashcards
Money-back guarantee
We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

Recommended explanations on Computer Science Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Explain why a class's copy constructor is called when an object of that class is passed by value into a function.

Short Answer

Step by step solution

What is a copy constructor?

Passing objects by value

Why is the copy constructor called?

Benefits of a copy constructor

Example

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Computer Science Textbooks

Problem Solving Techniques

Computer Programming

Game Design in Computer Science

Computer Organisation and Architecture

Data Structures

Data Representation in Computer Science

Study anywhere. Anytime. Across all devices.