Why the comparison function for the sort function in C + + (the third argument) is declared static

The comparison function in sort compare to be declared as a static member function or a global function, not as a normal member function, or an error will be made. Because a non-static member function is dependent on a specific object, and the Std::sort function is global, the non-static member function cannot be called in the sort. Static member functions or global functions are independent of the object and can be accessed independently without creating any object instances. Static member functions can not invoke non-static members of the class at the same time.

Why the comparison function for the sort function in C + + (the third argument) is declared static