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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: C String terminator
Date: Tue, 21 Jan 2020 10:41:17 -0800
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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:
> Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:
[...]
>> Correction #1: in this case, the critical point is that, here, printf()
>> expects a C "string" as it's second argument (as well as the first argument,
>> which is the given format string "[%s]\n").
> 
> Technically, that isn't right.  A %s conversion specifier requires
> as its argument a pointer to the first element of an array of
> character type, not a pointer to a string.  It is true in this
> particular case that the array must have a null character in it to
> avoid undefined behavior, but the argument description says "pointer
> to array of character type", and does not mention "string".
>
> (Also:  the possessive of "it" is "its", with no apostrophe.  The
> word "it's", with an apostrophe, is a contraction of "it is".)

I believe the reason it's described that way is that %s with a field
width can require a pointer that isn't necessarily a pointer to a
string.  For example, this is well defined:

    char not_a_string[3] = "foo";
    printf("%.3s\n", not_a_string);

The standard *could* have equivalently stated that a pointer to a string
is required when the format contains a "%s" directive, but that would
have made it overly wordy with no clear benefit.  A pointer to a string
*is* required for a "%s" directive, but the standard says so only
indirectly.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
    [Note updated email address]
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */