extern char *strncpy(char *dst, const char *src, size_t num);
extern char *strcat(char *dst, const char *src);
extern char *strdup(const char *src);
+extern char *strndup(const char *src, int length);
extern char *strchr(char *str, int character);
extern char *strrchr(char *str, int character);
extern char *strstr(char *str1, const char *str2);