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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 stringss1ands2.
The size passed to strncmp will be the size of segname.
I'm wondering what I should refer to.
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Many library functions accept a string or wide string argument with the constraint that the string they receive is properly null-terminated. Passing a character sequence or wide character sequence that is not null-terminated to such a function can result in accessing memory that is outside the bounds of the object.
The strncmp() built-in function compares at most the first count characters of the string pointed to by string1 to the string pointed to by string2. The string arguments to the function should contain a NULL character ( \0 ) marking the end of the string.
Yes, you need to do that. Not all functions put the null char for you, and strncpy , as I can read in its man page, requires to have a null byte among the first n characters of src.
If you don't include a terminating \0 you will commit a fundamental breach of contract.
According to the C99 standard, section 7.21.4.4, §3., it is legal:
The
strncmpfunction returns an integer greater than, equal to, or less than zero, accordingly as the possibly null-terminated array pointed to bys1is greater than, equal to, or less than the possibly null-terminated array pointed to bys2.
Notice, however, that it says array of characters. By definition, if an array of characters is not null-terminated, it is not a string.
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