member type
enum mask;

Character category bitmask type

This member type is inherited from ctype_base.

It is a bitmask type used as parameter for member functions is, scan_is and scan_not, and may take any bitwise combination of the following enum values:

spaceWhite-space character
printPrintable character
cntrlControl character
upperUppercase letter
lowerLowercase letter
alphaAlphabetic letter
digitDecimal digit
punctPunctuation mark
xdigitHexadecimal character

These categories are based on those defined in the C library header <cctype>. See the reference for cctype for the classification in these categories of characters of type char.