char *strtok_s(char *restrict s1, rsize_t *restrict s1max, const char *restrict s2, char **restrict ptr);
strtok_s is a reentrant version of the function strtok where the state is maintained in the object of type char * pointed to by ptr and the size of s1 is supplied in s1max. The parameters are checked for null pointers and on error the current constraint_handler is called.