s1

    On the first call, a pointer to a string containing zero or more
    text tokens. On all subsequent calls for that string, a NULL
    pointer.

 s2

    A pointer to a separator string consisting of one or more
    characters. The separator string may differ from call to call.

 s

    A null-terminated string that is a sequence of zero or more text
    tokens separated by spans of one or more characters from the
    separator string sep.

 sep

    A null-terminated string of separator characters. This separator
    string can be different from call to call.

 lasts

    A pointer that points to a user-provided pointer to stored
    information needed for strtok_r to continue scanning the same
    string.