ctype.h

• isxxxx Functions
• __toascii
• _tolower, tolower, _toupper, toupper

isxxxx Functions

Header

ctype.h

Prototype

int isalnum(int c);
int isalpha(int c);
int __isascii(int c);
int iscntrl(int c);
int __iscsym(int c);
int __iscsymf(int c);
int isdigit(int c);
int isgraph(int c);
int islower(int c);
int isprint(int c);
int ispunct(int c);
int isspace(int c);
int isupper(int c);
int isxdigit(int c);

Description

These macros, implemented as functions, test an integer value of a character (c) and return a non-zero value if the integer satisfies the test condition. If the integer does not satisfy the condition, these functions return 0. The ASCII character set is assumed. Only values of c between -1 and 255 are valid, except for __isascii, which is valid for any int. To invoke the function, undefine the macro name.

Synonym

Macros: isascii, iscsym, iscsymf

Return Value

The return values are listed in the following table:

Function	Returns non-zero if c is ...
isalnum	a letter or a digit.
isalpha	a letter.
__isascii	between 0 and 127.
iscntrl	a control character (0 to 0x1F), or c == 0x7F.
__iscsym	a letter, underscore or digit.
__iscsymf	a letter or underscore.
isdigit	the digits 0 to 9.
isgraph	a printing character (excluding the space).
islower	a lower-case character.
isprint	a printing character (including the space).
ispunct	a punctuation character.
isspace	a tab, linefeed, vertical tab, form feed, return, or space.
isupper	an upper-case character.
isxdigit	one of the characters 0 to 9, A to F, or a to f.

Compatibility

DOS Windows 3.x Phar Lap DOSX Win32

Example

/* 	Example for isXXXX */ 

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

void main () 
{   
   int test; 
   char *ans[2] = {" not ", ""}; 

   for (test = -1; test < 256; test++) 
   {   
      printf ("\n\n\nThe value %02x is :\n", 
	      test); 
      printf (" %salphanumeric\n", 
	      ans[(isalnum(test) != 0)]); 
      printf (" %sa letter\n", 
	      ans[(isalpha(test) != 0)]); 
      printf (" %sascii\n", 
	      ans[(__isascii(test) != 0)]); 
      printf (" %sa control\n", 
	      ans[(iscntrl(test) != 0)]); 
      printf (" %sa letter, 
	      underscore or digit\n", 
	      ans[(__iscsym(test) != 0)]); 
      printf (" %sa letter or underscore\n", 
	      ans[(__iscsymf(test) != 0)]); 
      printf (" %sa digit\n", 
	      ans[(isdigit(test) != 0)]); 
      printf (" %sprintable/ not a space\n", 
	      ans[(isgraph(test) != 0)]); 
      printf (" %slower case\n", 
	      ans[(islower(test) != 0)]); 
      printf (" %sprintable\n", 
	      ans[(isprint(test) != 0)]); 
      printf (" %sa punctuator\n", 
	      ans[(ispunct(test) != 0)]); 
      printf (" %swhite space\n", 
	      ans[(isspace(test) != 0)]); 
      printf (" %supper case\n", 
	      ans[(isupper(test) != 0)]); 
      printf (" %sa hexadecimal digit\n", 
	      ans[(isxdigit(test) != 0)]); 
      printf ("\n* Press a key for the next 
	      value*\n"); getch (); 
   } 
} 

Output

 The value ffff is : 
	not alphanumeric 
	not a letter 
	not ascii 
	not a control not a letter, underscore or digit 
	not a letter or underscore 
	not a digit 
	not printable/ not a space 
	not lower case 
	not printable 
	not a punctuator 
	not white space 
	not upper case 
	not a hexadecimal digit 

 *Press a key for the next value* 
 . . . 


The value 41 is : 
	alphanumeric 
	a letter 
	ascii 
	not a control a letter, underscore or digit 
	a letter or underscore 
	not a digit 
	printable/ not a space 
	not lower case 
	printable 
	not a punctuator 
	not white space 
	upper case 
	a hexadecimal digit 

 *Press a key for the next value* 
 . . . 

__toascii

Header

ctype.h

Prototype

int __toascii(int c);

Description

The __toascii function converts c to a character by taking any integer value and discarding all but the low order seven bits making up an ASCII character. If c is already a valid character, then it is returned unchanged. Implemented as a macro in ctype.h, __toascii is also included as a function within the library. Undefining the macros, or not including ctype.h, will cause the library functions to be used.

Synonym

Function: toascii

Return Value

Returns the low seven bits of c. There is no error return.

Compatibility

DOS Windows 3.x Phar Lap DOSX Win32

Example

See _tolower

_tolower, tolower, _toupper, toupper

Header

ctype.h

Prototype

int _tolower(int c); int tolower(int c);
int _toupper(int c); int toupper(int c);

Description

The tolower function converts any integer value c in the range of 'A' -'Z' to lowercase. The _tolower function is special version of tolower which is intended for use only when c is uppercase. If _tolower encounters a value that is not an uppercase letter, the result is undefined.
toupper converts to uppercase the integer value c in the range of 'a' -'z'. Function _toupper is a special version of toupper that is intended for use only when c is lowercase. If _toupper encounters a value that is not a lowercase letter, the result is undefined.
These functions are implemented as macros in ctype.h, and are also included as functions within the library. Undefining the macros, or not including ctype.h, defaults to usage of the library functions.

Return Value

tolower returns c, converted to lower case if it was uppercase, otherwise c is returned unchanged. toupper returns c, converted to upper case if it was lower case, otherwise c is returned unchanged. If _tolower and _toupper encounter an invalid character, the result is undefined.

Compatibility

DOS Windows 3.x Phar Lap DOSX Win32

Example

/* 	Example for tolower 
	Also demonstrates _toascii, _tolower, 
	toupper, _toupper */ 

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

void main () 
{   
   char *str =
      "Moral indignation is jealousy with a halo. - H. G. Wells";
 
   char *p;

   printf("Original string: \"%s\"\n", str); 

   printf("After tolower:   \""); 
   for (p = str; *p; p++) 
      printf("%c", tolower (* p)); 
   printf("\"\n"); 

   printf("After toupper:   \""); 
   for (p = str; *p; p++) 
      printf("% c", toupper (* p)); 
   printf ("\"\n"); 
} 

Output

Original string: "Moral indignation is jealousy with a halo. - H. G. Wells"
After tolower:   "moral indignation is jealousy with a halo. - h. g. wells"
After toupper:   "MORAL INDIGNATION IS JEALOUSY WITH A HALO. - H. G. WELLS"