Is it legal to pass a non-null-terminated string to strncmp in C?

Question

I have an array of 16 bytes that holds the name of an executable's segment.

char segname[16];

If the segment name length is less than 16 bytes, then the rest is padded with null bytes. Otherwise, there is no terminating null byte.

I want to compare segname to various strings, e.g. __text.

Is it legal to call strncmp with a non-null-terminated string?

This post assumes it is legal. This source code makes it legal too. But my man's page says:

The strncmp() function lexicographically compares the null-terminated strings s1 and s2.

The size passed to strncmp will be the size of segname.

I'm wondering what I should refer to.

Answer 1

According to the C99 standard, section 7.21.4.4, §3., it is legal:

The strncmp function returns an integer greater than, equal to, or less than zero, accordingly as 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.

Notice, however, that it says array of characters. By definition, if an array of characters is not null-terminated, it is not a string.