isalpha(c)

isupper(c)

islower(c)

isdigit(c)

isxdigit(c)

isalnum(c)

isspace(c)

ispunct(c)

isprint(c)

isgraph(c)

iscntrl(c)

isascii(c)

_toupper(c)

_tolower(c)

toupper(c)

tolower(c)

toascii(c)

isalpha

c is a letter, a-z or A-Z

isupper

c is an upper case letter, A-Z

islower

c is a lower case letter, a-z

isdigit

c is a digit, 0-9

isxdigit

c is a hexadecimal digit, 0-9 or a-f or A-F

isalnum

c is an alphanumeric character, a-z or A-Z or 0-9

isspace

c is a space, horizontal tab, newline, vertical tab, formfeed, or carriage return (0x20, 0x9, 0xA, 0xB, 0xC, 0xD)

ispunct

c is a punctuation character (one of !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~)

isprint

c is a printing character, 0x20 (space) through 0x7E (tilde)

isgraph

c is a visible printing character, 0x21 (exclamation) through 0x7E (tilde)

iscntrl

c is a delete character, 0x7F, or ordinary control character, 0x0 through 0x1F

isascii

c is an ASCII character, 0x0 through 0x7F

Toascii is not a classification macro; it converts its argument to ASCII range by anding with 0x7F.

If c is an upper case letter, tolower returns the lower case version of the character; otherwise it returns the original character. Toupper is similar, returning the upper case version of a character or the original character. Tolower and toupper are functions; _tolower and _toupper are corresponding macros which should only be used when it is known that the argument is upper case or lower case, respectively.

/sys/include/ctype.h

for the macros.

/sys/src/libc/port/ctype.c

for the tables.