Re: [review] manual: Clarify strnlen, wcsnlen, strndup null termination behavior

[Florian Weimer <fweimer at redhat dot com>]

* Andreas Schwab:

> On Okt 30 2019, Florian Weimer wrote:
>
>> * Andreas Schwab:
>>
>>> On Okt 30 2019, Florian Weimer (Code Review) wrote:
>>>
>>>> +Note that @var{s} must be an array of at least @var{maxlen} bytes.  It
>>>> +is undefined to call @code{strnlen} on a shorter array, even if it is
>>>> +known that the shorter array contains a null terminator.
>>>
>>> This is not true.  strnlen _always_ stops before the null byte.
>>
>> This is not how it is specified in POSIX.
>
> Yes, it is.
>
>     The strnlen() function shall return the number of bytes preceding
>     the first null byte in the array to which s points, if s contains a
>     null byte within the first maxlen bytes; otherwise, it shall return
>     maxlen.
>
> There is nothing undefined here.  Your interpretation would be
> completely useless anyway.

It says “array”, which implies a length.  Admittedly, it does not say
that maxlen corresponds to the arrray length.  POSIX also says this:

| The strnlen() function shall never examine more than maxlen bytes of
| the array pointed to by s.

But it does NOT say that reading stops after the first null terminator.

Thanks,
Florian