In the following code the constructor is called only once (ie) 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" << '\n';
}
Car(Car &obj)
{
std::cout << "Copy constructor" << '\n';
}
};
int main()
{
Car();
Car o1(Car()); // not calling any constructor
return 0;
}
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.
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