On Tue, 02 Jan 2024 19:59:57 -0800
Kaz Kylheku <k...@kylheku.com> wrote:
> On 2024-01-02 16:11, Takashi Yano via Cygwin wrote:
> > Perhaps, the off-by-one is for EOF as you guess.
>
> I doubt it. If EOF were out of range of char, it would have to be -129 or
> less,
> so that -127 would look even more wrong.
>
> I see EOF is just -1. That value will also be produced by '\xFF', or
> "\xff"[0], etc.
In systems other than cygwin, ALLOW_NEGATIVE_CTYPE_INDEX might not
be set. In that case,
124 const char _ctype_[1 + 256] = {
125 0,
126 _CTYPE_DATA_0_127,
127 _CTYPE_DATA_128_255
128 };
is used for __CTYPE_PTR.
So, isalpha(EOF) reffers to 0 in line 125 via this trick.
45 int
46 isalpha (int c)
47 {
48 return(__CTYPE_PTR[c+1] & (_U|_L));
49 }
In cygwin, both isalpha((char*)0xff) and isalpha(EOF) reffers to
_CTYPE_DATA_128_255[127] in line 89, while isalpha((unsigned char*)0xff)
reffers to _CTYPE_DATA_128_255[127] in line 91.
88 char _ctype_b[128 + 256] = {
89 _CTYPE_DATA_128_255,
90 _CTYPE_DATA_0_127,
91 _CTYPE_DATA_128_255
92 };
--
Takashi Yano <takashi.y...@nifty.ne.jp>
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