class - C++ constructor not called

Question

In the following code the constructor is called only once (i.e.) when Car() executes. Why is it not called the second time on the statement Car o1(Car())?

#include <stdio.h>
#include <iostream>

class Car
{
public :
   Car()
   {
      std::cout << "Constructor" << '
';
   }
   Car(Car &obj)
   {
      std::cout << "Copy constructor" << '
';
   }
};

int main()
{
   Car();
   Car o1(Car()); // not calling any constructor
   return 0;
}

Answer 1

Car o1(Car());

This declares a function called o1 that returns a Car and takes a single argument which is a function returning a Car. This is known as the most-vexing parse.

You can fix it by using an extra pair of parentheses:

Car o1((Car()));

Or by using uniform initialisation in C++11 and beyond:

Car o1{Car{}};

But for this to work, you'll need to make the parameter type of the Car constructor a const Car&, otherwise you won't be able to bind the temporary to it.