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The isnumber function behaves similarly to isdigit, 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 _l-suffixed versions take an explicit locale argument, whereas the non-suffixed versions use the current global or per-thread locale.
The isdigit and isnumber functions return zero if the character tests false and return 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 iswdigit function should be used instead.
The isdigit function conforms to -isoC. The isdigit_l function conforms to -p1003.1-2008.
The isnumber function appeared in BSD 4.4 .