Question

From my understanding of declarations and definitions, at the global scope:

MyClass instance();//Declares a function that returns a MyClass
MyClass instance;//Declares an instance of MyClass

Is it possible to declare a variable and define it to use the default constructor at global scope? What if I was using a structure instead of a class?

EDIT:

Okay, so MyClass instance; does call the default constructor. Can anyone explain how this is consistent with this example:

int a; // not default constructed, will have random data 
int b = int(); // will be initialised to zero

Answer 1

MyClass instance;

will invoke the default constructor (i.e. the constructor with no parameters).

This is counter-intuitive, because to invoke an overloaded constructor with parameters you would do the following:

MyClass instance(param1, param2);

Logic would tell you that you pass in an empty argument list to invoke the default constructor, but the following code…

MyClass instance();

…looks like a prototype to the compiler rather than the construction of a MyClass object.

There is no difference between a struct and a class in C++, except that a struct has public members by default and a class has private members by default.