Chapter 14: Problem 25

Why is a class's copy constructor called when an object of that class is passed by value into a function?

Short Answer

Expert verified

Answer: A copy constructor is called when an object of a class is passed by value into a function because, in the process of passing by value, a separate copy of the object is created in the function's parameter. Since it is a copy, the object's copy constructor is used to create that copy and initialize it with the values of the original object.

Step by step solution

Defining a copy constructor

A copy constructor is a special constructor in a class that is used to create an exact copy of an existing object of the same class. It is called when an object is initialized as a copy of another object of the same class. The syntax for a copy constructor is: ``` className(const className &obj) ``` Here, `className` is the class name and `&obj` is a reference to the object being copied.

Understanding passing by value

When we pass objects to a function, there are two ways in which they can be passed: by value and by reference. In passing by value, the value of the argument is copied into the parameter of the function. In other words, the parameter in the function has a memory space separate from the argument, so any changes made inside the function do not affect the argument outside the function.

Connection between copy constructor and passing by value

When an object is passed by value into a function, a copy of the object is created in the function's parameter. Since it is a copy, the object's copy constructor is called to create the copy. So, the link between these two concepts is that passing an object of a class by value into a function requires the use of its copy constructor.

Example

Here's an example to demonstrate this link between passing by value and copy constructor: ```cpp #include using namespace std; class MyClass { public: int x; MyClass(int a) : x(a) {} MyClass(const MyClass &obj) { x = obj.x; cout << "Copy constructor called." << endl; } }; void func(MyClass obj) { obj.x += 3; } int main() { MyClass sample_object(5); func(sample_object); cout << "Object's value after function call: " << sample_object.x << endl; return 0; } ``` In this example, when the `func` function is called, the `MyClass` object `sample_object` is passed by value. Since we're passing it by value, the copy constructor is called to create the copy of the object inside the function. The output of the program will be: ``` Copy constructor called. Object's value after function call: 5 ``` This shows that the copy constructor is called when an object of a class is passed by value into a function.

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Why is a class's copy constructor called when an object of that class is passed by value into a function?

Short Answer

Step by step solution

Defining a copy constructor

Understanding passing by value

Connection between copy constructor and passing by value

Example

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