How is this possible to use in c++?

Question

1. To my surprise, I found that the name of a c++ object can be the same as class name. Can someone explain to me the reason why?
2. When I declare an object of class a as a a1(), it does not raise an error, but doesn't call the constructor. Why is this happening?

My code:

#include<iostream>
using namespace std;

class a 
{
    public:
    a() 
    {
        cout << "in a\n";
    }
};

int main()
{
    a a1();
    a a;
}

Answer 1

When you write a a1(); it is actually being parsed as a function declaration not a call to the default constructor.

a a1;

will call the default constructor correctly

When you write a a; it works because the variable name takes preference over the class name in what is called name hiding, but even though it works it will only lead to confusion and I would avoid doing it.

And for all those people who like standards quotes here you go

A class name (9.1) or enumeration name (7.2) can be hidden by the name of a variable, data member, function, or enumerator declared in the same scope. If a class or enumeration name and a variable, data member, function, or enumerator are declared in the same scope (in any order) with the same name, the class or enumeration name is hidden wherever the variable, data member, function, or enumerator name is visible.