4.3BSD - /usr/man/cat3/tolower.0

CTYPE(3)                                                              CTYPE(3)


NAME
       isalpha,   isupper,   islower,  isdigit,  isxdigit,  isalnum,  isspace,
       ispunct, isprint, isgraph, iscntrl, isascii, toupper, tolower,  toascii
       - character classification macros

SYNOPSIS
       #include <ctype.h>

       isalpha(c)

       . . .

DESCRIPTION
       These macros classify ASCII-coded integer values by table lookup.  Each
       is a predicate returning nonzero for true, zero for false.  Isascii and
       toascii  are  defined  on all integer values; the rest are defined only
       where isascii is true and  on  the  single  non-ASCII  value  EOF  (see
       stdio(3S)).

       isalpha        c is a letter

       isupper        c is an upper case letter

       islower        c is a lower case letter

       isdigit        c is a digit

       isxdigit       c is a hex digit

       isalnum        c is an alphanumeric character

       isspace        c  is  a  space, tab, carriage return, newline, vertical
                      tab, or formfeed

       ispunct        c  is  a  punctuation  character  (neither  control  nor
                      alphanumeric)

       isprint        c  is  a printing character, code 040(8) (space) through
                      0176 (tilde)

       isgraph        c is a printing character,  similar  to  isprint  except
                      false for space.

       iscntrl        c is a delete character (0177) or ordinary control char‐
                      acter (less than 040).

       isascii        c is an ASCII character, code less than 0200

       tolower        c is converted to lower case.  Return value is undefined
                      if not isupper(c).

       toupper        c is converted to upper case.  Return value is undefined
                      if not islower(c).

       toascii        c is converted to be a valid ascii character.

SEE ALSO
       ascii(7)


7th Edition                      May 12, 1986                         CTYPE(3)