#include <string.h>

char *strtok(char *s1, CONST char *s2)
	{	/* find next token in s1[] delimited by s2[] */
	char *sbegin, *send;
	static char *ssave = "";	/* for safety */

	sbegin = (s1) ? s1 : ssave;
	sbegin += strspn(sbegin, s2);
	if (*sbegin == '\0')
		{	/* end of scan */
		ssave = "";				/* for safety */
		return 0;
		}
	send = strpbrk(sbegin, s2);
	if (*send != '\0')
		*send++ = '\0';
	ssave = send;
	return sbegin;
	}