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The ishexnumber function behaves similarly to isxdigit, but may recognize additional characters, depending on the current locale setting.
The value of the argument must be representable as an
.Vt unsigned char or the value of EOF.
The isxdigit function returns zero if the character tests false and returns non-zero if the character tests true.
The BSD 4.4 extension of accepting arguments outside of the range of the
.Vt unsigned char type in locales with large character sets is considered obsolete and may not be supported in future releases. The iswxdigit function should be used instead.
The isxdigit function conforms to -isoC.
The ishexnumber function appeared in BSD 4.4 .