Why do I get a compilation error with this declaration? [duplicate]

This question already has an answer here:

• Most vexing parse: why doesn't A a(()); work? 5 answers

I can't understand why I get this error with the GCC compiler:

#include <string>
using namespace std;

void main()
{
   string s();
   s = "wtf";
   return 0;
}

// output: error: non-object type 'std::string ()' is not assignable

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Yes, yes, fine, I was after 30 Minutes or Less. Didn't go so well.

But since you're all keen to point out that I know what I'm talking about in reality, you should read up on the most vexing parse because this is not it!!