The strxfrm function transforms the string pointed to by s2,
    and stores the resulting string in the array pointed to by s1.
    No more than maxchar bytes, including the null terminator, are
    placed into the array pointed to by s1.

    If the value of maxchar is less than the required size to store
    the transformed string (including the terminating null), the
    contents of the array pointed to by s1 is indeterminate. In such
    a case, the function returns the size of the transformed string.

    If maxchar is 0, then s1 is allowed to be a NULL pointer, and the
    function returns the required size of the s1 array before making
    the transformation.

    The string comparison functions, strcoll and strcmp, can produce
    different results given the same two strings to compare. The
    reason for this is that strcmp does a straightforward comparison
    of the code point values of the characters in the strings,
    whereas strcoll uses the locale information to do the comparison.
    Depending on the locale, the strcoll comparison can be a
    multipass operation, which is slower than strcmp.

    The purpose of the strxfrm function is to transform strings in
    such a way that if you pass two transformed strings to the strcmp
    function, the result is the same as passing the two original
    strings to the strcoll function. The strxfrm function is useful
    in applications that need to do a large number of comparisons on
    the same strings using strcoll. In this case, it might be more
    efficient (depending on the locale) to transform the strings once
    using strxfrm, and then do comparisons using strcmp.