The strcmp and strncmp functions lexicographically compare the null-terminated strings s1 and s2.
The strncmp function compares not more than len characters. Because strncmp is designed for comparing strings rather than binary data, characters that appear after a \0 character are not compared.
The strcmp and strncmp return an integer greater than, equal to, or less than 0, according as the string s1 is greater than, equal to, or less than the string s2. The comparison is done using unsigned characters, so that \200 is greater than \0.
bcmp(3), memcmp(3), strcasecmp(3), strcoll(3), strxfrm(3)