int strncmp(const char *s1, const char *s2, size_t n);
strncmp compares not more than n characters from the array pointed to by s1 to the array pointed to by s2. Characters that follow a null character are not compared.
strncmp returns an integer greater than, equal to, or less than zero, if the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2.