Character Categorization Functions

These functions return a non-zero (true) value if the argument is an ascii character in the indicated category:

• isalnum - Alphabetic characters or digits, A..Z, a..z, or 0..9
• isalpha - Alphabetic characters, A..Z or a..z
• isascii - ASCII characters, char (0) thru char (127)
• iscntrl - char (0) .. char (31), char (127)
• isdigit - Digit characters, 0..9
• isgraph - Printable ASCII characters, including the space character
• islower - Lower case alphabetic characters, a..z
• isprint - Printable ASCII characters, excluding the space character
• ispunct - Punctuation characters, excluding the alphanumeric characters, space, and control characters
• isspace - Whitespace characters: space, horizontal tab, vertical tab, carriage return, line feed
• isupper - Upper case alphabetic characters, A..Z
• isxdigit - Hexadecimal Digit characters, 0..9, A..F, a..f

Except for isascii, the return value is undefined if the argument is not an ascii character.  These functions may be implemented as macros.

Value

The character to be tested.

0

The character is not in the category.

>0

The character is in the category.  The actual value returned is implementaion dependent.

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

void Display (int (*isX) (int));

void Init ();  

char * D[128];

int main () {
  Init ();
  printf ("isalnum\n");
  Display (&isalnum);
  printf ("isalpha\n");
  Display (&isalpha);
  printf ("isascii\n");
  Display (&isascii);
  printf ("iscntrl\n");
  Display (&iscntrl);
  printf ("isdigit\n");
  Display (&isdigit);
  printf ("isgraph\n");
  Display (&isgraph);
  printf ("islower\n");
  Display (&islower);
  printf ("isprint\n");
  Display (&isprint);
  printf ("ispunct\n");
  Display (&ispunct);
  printf ("isspace\n");
  Display (&isspace);
  printf ("isupper\n");
  Display (&isupper);
  printf ("isxdigit\n");
  Display (&isxdigit);
  return 0;
}

void Display (int (*isX) (int)) {
  int i;
  int Begin;
  int Current;
  Begin = 0;
  Current = isX (0);
  i = 0;
  while (i < 128) {
    if ((isX (i) != Current) && (i > 1)) {
      printf ("  %s..%s: %i\n",  D[Begin], D[i - 1], Current);
      Begin = i;
      Current = isX (i);
    }
    ++i;
  }
  printf ("  %s..%s: %i\n",  D[Begin], D[i - 1], Current);
}

void Init () {
  int i;
  i = 0;
  while (i < 32) {
    D [i] = (char *) malloc (7);
    D [i][0] = '\'';
    D [i][1] = '\\';
    D [i][2] = '0' + ((i >> 6) & 7);
    D [i][3] = '0' + ((i >> 3) & 7);
    D [i][4] = '0' + (i & 7);
    D [i][5] = '\'';
    D [i][6] = 0;
    ++i;
  }
  while (i < 127) {
    D [i] = (char *) malloc (4);
    D [i][0] = '\'';
    D [i][1] = i;
    D [i][2] = '\'';
    D [i][3] = 0;
    ++i;
  }
  D[0] = "\'\\0\'";
  D['\\'] = "\'\\\\\'";
  D['\"'] = "\'\\\"\'";
  D['\''] = "\'\\\'\'";
  D['\?'] = "\'\\\?\'";
  D['\a'] = "\'\\a\'";
  D['\b'] = "\'\\b\'";
  D['\f'] = "\'\\f\'";
  D['\n'] = "\'\\n\'";
  D['\r'] = "\'\\r\'";
  D['\t'] = "\'\\t\'";
  D['\v'] = "\'\\v\'";
  D[127] = "\'\\177\'";
}

isalnum
  '\0'..'/': 0
  '0'..'9': 4
  ':'..'@': 0
  'A'..'Z': 256
  '['..'`': 0
  'a'..'z': 256
  '{'..'\177': 0
isalpha
  '\0'..'@': 0
  'A'..'Z': 256
  '['..'`': 0
  'a'..'z': 256
  '{'..'\177': 0
isascii
  '\0'..'\177': 1
iscntrl
  '\0'..'\037': 32
  ' '..'~': 0
  '\177'..'\177': 32
isdigit
  '\0'..'/': 0
  '0'..'9': 4
  ':'..'\177': 0
isgraph
  '\0'..' ': 0
  '!'..'/': 16
  '0'..'9': 132
  ':'..'@': 16
  'A'..'F': 384
  'G'..'Z': 256
  '['..'`': 16
  'a'..'f': 384
  'g'..'z': 256
  '{'..'~': 16
  '\177'..'\177': 0
islower
  '\0'..'`': 0
  'a'..'z': 2
  '{'..'\177': 0
isprint
  '\0'..'\037': 0
  ' '..' ': 64
  '!'..'/': 16
  '0'..'9': 132
  ':'..'@': 16
  'A'..'F': 384
  'G'..'Z': 256
  '['..'`': 16
  'a'..'f': 384
  'g'..'z': 256
  '{'..'~': 16
  '\177'..'\177': 0
ispunct
  '\0'..' ': 0
  '!'..'/': 16
  '0'..'9': 0
  ':'..'@': 16
  'A'..'Z': 0
  '['..'`': 16
  'a'..'z': 0
  '{'..'~': 16
  '\177'..'\177': 0
isspace
  '\0'..'\b': 0
  '\t'..'\r': 8
  '\016'..'\037': 0
  ' '..' ': 8
  '!'..'\177': 0
isupper
  '\0'..'@': 0
  'A'..'Z': 1
  '['..'\177': 0
isxdigit
  '\0'..'/': 0
  '0'..'9': 128
  ':'..'@': 0
  'A'..'F': 128
  'G'..'`': 0
  'a'..'f': 128
  'g'..'\177': 0