A function object can be unary or binary. logical_not, and negate are unary function objects.
Here are binary function objects: plus, minus, multiplies, divides, modulus, equal_to, not_equal_to, greater, greater_equal, less, less_equal, logical_and, logical_or
Built-in Function objects: A built in function object is the one that overloads the operator() function Header <functional> must be used for built in function objects.
Syntax to call a function object: