CompareDataFunc

Specifies the type of a comparison function used to compare two values.

The function should return a negative integer if the first value comes before the second, 0 if they are equal, or a positive integer if the first value comes after the second.

Parameters:

a	a value
b	a value to compare with
user_data	user data

Returns:

negative value if a < b; zero if a = b; positive value if a > b