Explicit Call to a Constructor

Question

I know the concept that we can call the Constructor both Explicitly and Implicitly, and i have tested both the scenarios(generally till now my all purp

Answer 1

There are three ways a constructor can be called:

• Implicitly, by declaring an instance of the type without initializing it
• Also implicitly, by either initializing an instance with = or by causing an implicit conversion from the argument type to your class.
• Explicitly calling the constructor, passing arguments.

Which of these you can use in a particular context depends on the constructors you're calling.

class Foo 
{
    Foo();                                  // 1
    Foo(int a);                             // 2
    explicit foo(const std::string& f);     // 3
    Foo(int c, int d);                      // 4
};

1. This constructor will be called implicitly when declaring Foo f;. Never attempt to call a constructor without arguments explicitly, as Foo f(); will declare a function!
2. This one can be called by writing Foo f = 42; or Foo f(42).
3. The explicit keyword forbids implicit conversion by writing Foo f = std::string("abc"); or function_taking_foo(function_returning_string());.
4. As there are multiple arguments, the explicit version is the only suitable.