#define _XOPEN_SOURCE 500
#include <string.h>
char *strtok_r(char *s, const char *sep, char **lasts);The function strtok_r() considers the NULL-terminated string s as a sequence of zero or more text tokens separated by spans of one or more characters from the separator string sep. The argument lasts points to a user-provided pointer which points to stored information necessary for strtok_r() to continue scanning the same string.
In the first call to strtok_r(), s points to a NULL-terminated string, sep to a NULL-terminated string of separator characters and the value pointed to by lasts is ignored. The function strtok_r() returns a pointer to the first character of the first token, writes a NULL character into s immediately following the returned token, and updates the pointer to which lasts points.
In subsequent calls, s is a NULL pointer and lasts will be unchanged from the previous call so that subsequent calls will move through the string s, returning successive tokens until no tokens remain. The separator string sep may be different from call to call. When no token remains in s, a NULL pointer is returned.
If successful, strtok_r() returns a pointer to the token found.
When no token is found, strtok_r() returns a NULL pointer.