3.1 Character-Classification Functions

The character-classification functions take a single argument on which they perform a logical operation. The argument can have any value; it does not have to be an ASCII character. The isascii function determines if the argument is an ASCII character (0 through 177 octal). The other functions determine whether the argument is a particular type of ASCII character, such as a graphic character or digit. The isw* functions test wide characters. Character- classification information is in the LC_CTYPE category of the program's current locale.

For all functions, a positive return value indicates TRUE. A return value of 0 indicates FALSE.

To briefly reference the character-classification functions in a subsequent table, each function is assigned a number, as shown in Table 3-2.

Table 3-2 Character-Classification Functions

Table 3-3 lists the numbers of the functions (as assigned in Table 3-2) that return the value TRUE for each of the given ASCII characters. The numeric code represents the octal value of each of the ASCII characters.

Table 3-3 ASCII Characters and the Character- Classification Functions

Example 3-1 shows how the character- classification functions are used.

Example 3-1 Character-Classification Functions

/* This example uses the isalpha, isdigit, and isspace functions *
 * to count the number of occurrences of letters, digits, and    *
 * white-space characters entered through the standard input     *
 * (stdin).                                                      */

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

main()
{
   char c;
   int i = 0, j = 0, k = 0;
   while ((c = getchar()) != EOF)
      {
         if (isalpha(c))
            i++;
         if (isdigit(c))
            j++;
         if (isspace(c))
            k++;
      }

   printf("Number of letters: %d\n", i);
   printf("Number of digits:  %d\n", j);
   printf("Number of spaces:  %d\n", k);
}

The sample input and output from Example 3-1 follows:

$ RUN  EXAMPLE1
I saw 35 men with mustaches on Christopher Street.<Return>
<Ctrl/Z>
Number of letters: 39
Number of digits:  2
Number of spaces:  9
$