C++: What is the difference between List x; & List x()?

Question

I know that list is used in C++ as we use linked list in C lang. Now, I want to know when forward list is used ?

Answer 1

There exists a big difference which is explained via a code below:
• Let, List is a name of any class.

Then function f() evokes a local List object x:

void f()
{
List x; // Local object x 
// Sample code...

}

But the function g() invokes f() which eventually returns a List:

void g()
{
List x(); // function which returns the List
// Sample code...
}