The stpncpy function copies at most n characters from the string pointed to by src, including the terminating '\0' character, to the array pointed to by dest. Exactly n characters are written at dest. If the length strlen(src) is smaller than n, the remaining characters in the array pointed to by dest are filled with '\0' characters. If the length strlen(src) is greater or equal to n, the string pointed to by dest will not be '\0' terminated. The strings may not overlap. The programmer must ensure that there is room for at least n characters at dest.
stpncpy returns a pointer to the terminating null in dest, or, if dest is not null-terminated, dest + n.