list test() and list test difference?

Question

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Error on calling default constructor with empty set of brackets
What's the differences between Test t; and Test t();? if Test is a class

What is the difference between this code the first compiles the second doesn't. I am pretty new to C++.

FIRST SAMPLE

list<string> str;
list<string>::iterator it;

it = str.begin();

SECOND SAMPLE

list<string> str();
list<string>::iterator it;

it = str.begin();

I thought that calling without the parantethiss calls the default constructor witch is the same to () variant.

Answer 1

list<string> str;

declares a variable.

list<string> str();

declares a function that takes no parameters and returns a list<string>.

This is commonly known as a vexing parse.

Answer 2

list<string> str(); is treated as a function prototype declaration. See "Most Vexing Parse".