Why is :: (scope) used with empty left-hand operand? [duplicate]

Question

I've seen this a few times now, and I've been scratching my head wondering why...

As an example: (http://www.codeguru.com/forum/showthread.php?t=377394)

void LeftClick ( )
{  
  INPUT    Input={0};
  // left down 
  Input.type      = INPUT_MOUSE;
  Input.mi.dwFlags  = MOUSEEVENTF_LEFTDOWN;
  ::SendInput(1,&Input,sizeof(INPUT));

  // left up
  ::ZeroMemory(&Input,sizeof(INPUT));
  Input.type      = INPUT_MOUSE;
  Input.mi.dwFlags  = MOUSEEVENTF_LEFTUP;
  ::SendInput(1,&Input,sizeof(INPUT));
}

This example works without the :: (scope) operators so why are they even there?

Answer 1

This basically mean "get the GLOBAL scoped function, instead of the currently visible one".

void SendInput() { /* (1) */
}

namespace derp {
    void SendInput() { /* (2) */
    }

    void LeftClick() {
        ...
        ::SendInput(); /* matches (1) */
        SendInput();  /* matches (2) */
    }
}