Question

I’m looking at the IsCharAlphaNumeric Windows API function. As it only takes a single TCHAR, it obviously can’t make any decisions about surrogate pairs for UTF16 content. Does that mean that there are no alphanumeric characters that are surrogate pairs?

Answer 1

Characters outside the BMP can be letters. (Michael Kaplan recently discussed a bug in the classification of the character U+1F48C.) But IsCharAlphaNumeric cannot see characters outside the BMP (for the reasons you noted), so you cannot obtain classification information for them that way.

If you have a surrogate pair, call GetStringType with cchSrc = 2 and check for C1_ALPHA and C1_DIGIT.

Edit: The second half of this answer is incorrect GetStringType does not support surrogate pairs.