David Laight <david@l8s.co.uk> wrote:
> 
> The (int) cast only gets rid of a warning genberated by some compilers.
> 
> The problem is that if 'c' is a signed char, then it is promoted to
> a signed integer using by preserving the sign.  This does not DTRT
> for any of the isXXX() functions.


I'll see now. IYSS, how about (int)((unsigned char)c)?
So, the ctype convertion inside isXXXX() functions will looks like:

    #define isXXXX(c)  ((int)((_ctype_ + 1)[(int)((unsigned char)(c))] & (CTYPE_FLAGS)))

This causes the index [(int)((unsigned char)(c))] will always return
a positive value, even in signed int.

--
BR, Mishka.