How can I check in Win32 whether a Unicode character is any kind of digit?

Suppose you have a Unicode code unit wchar_t and you want to know whether it represents a numeric digit. If you have the ICU library, you can check if its code point’s u_charType is U_DECIMAL_DIGIT_NUMBER. But what about plain Win32?

For Win32, you can use the Get­String­TypeW function to obtain properties for each code unit.

bool IsUnicodeDigit(wchar_t ch)
{
    WORD type;
    return GetStringTypeW(CT_CTYPE1, &ch, 1, &type) &&
           (type & C1_DIGIT);
}

We ask the Get­String­TypeW function for the CT_CTYPE1 value for one character, passing an output buffer of size 1. We then check whether the result says that it is a digit.

The Get­String­TypeW function produces a 16-bit value for each provided code unit. There are more than 16 things you can ask about, so they are broken into groups, and you specify which group you want. Group 1 contains the basic classifications that support POSIX functions like isdigit and isalnum.

Here’s one way it could be done. (I’m not saying this is how it actually is done.)

C runtime	Category flags	Win32 function
isalnum	C1_ALPHA | C1_UPPER | C1_LOWER | C1_DIGIT	IsCharAlphaNumeric sort of
isalpha	C1_ALPHA | C1_UPPER | C1_LOWER	IsCharAlpha sort of
isblank	C1_BLANK
iscntrl	C1_CNTRL
isdigit	C1_DIGIT
isgraph	C1_ALPHA | C1_UPPER | C1_LOWER | C1_DIGIT | C1_PUNCT
islower	C1_LOWER	IsCharLower
isprint	C1_ALPHA | C1_UPPER | C1_LOWER | C1_DIGIT | C1_PUNCT | C1_BLANK
ispunct	C1_PUNCT
isspace	C1_SPACE
isupper	C1_UPPER	IsCharUpper
isxdigit	C1_XDIGIT

Bonus reading: The difference between C1_SPACE-ing out and drawing a C1_BLANK.