Am Freitag, den 17.04.2015, 20:35 +0200 schrieb Szabolcs Nagy:
> #define isdigit(a) (((0?1U:(a))-'0') < 10)
> 
> which works when the conversion rank of a is <= unsigned

but not if it has conversion rank larger then unsigned and the result
of the substraction has a negative result. So what you think of

#define isdigit(a) (((0?1ULL:(a))-'0') < 10ULL)

This ensures that the type of the left is always ullong, so the
substraction overflows to something big if a is not a digit.

Jens


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