Why is the copy constructor called when we pass an object as an argument by value to a method?

Question

Why is the copy constructor called when I pass an object as an argument by value to a function? Please see my below code: I am passing an object of a class as an argument by

Answer 1

Because passing by value to a function means the function has its own copy of the object. To this end, the copy constructor is called.

void display(ClassA obj)
{
   // display has its own ClassA object, a copy of the input
   cout << "Hello World" << endl;
}

Bear in mind that in some cases copies may be elided, for instance, if a temporary value is passed to the function.