isxdigit is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero for hexadecimal digits, and 0 for other characters. It is defined only when isascii(c) is true or c is EOF.
You can use a compiled subroutine instead of the macro definition by undefining the macro using `#undef isxdigit'.### Returns
isxdigit returns non-zero if c is a hexadecimal digit (0--9, a--f, or A--F).
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**Authoritative source**: BUSMASTER DITA help source `isxdigit.dita`, compiled into `BUSMASTER.CHM` with the application.
