Default constructor with empty brackets

Question

Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?

MyObject  object;  // ok - default ctor
MyObject  object(blah); // ok

MyObject  object();  // error

I seem to type "()" automatically everytime. Is there a good reason this isn't allowed?

Answer 1

Most vexing parse

This is related to what is known as "C++'s most vexing parse". Basically, anything that can be interpreted by the compiler as a function declaration will be interpreted as a function declaration.

Another instance of the same problem:

std::ifstream ifs("file.txt");
std::vector<T> v(std::istream_iterator<T>(ifs), std::istream_iterator<T>());

v is interpreted as a declaration of function with 2 parameters.

The workaround is to add another pair of parentheses:

std::vector<T> v((std::istream_iterator<T>(ifs)), std::istream_iterator<T>());

Or, if you have C++11 and list-initialization (also known as uniform initialization) available:

std::vector<T> v{std::istream_iterator<T>{ifs}, std::istream_iterator<T>{}};

With this, there is no way it could be interpreted as a function declaration.