Arduino - Character Functions

All data is entered into computers as characters, which includes letters, digits and various special symbols. In this section, we discuss the capabipties of C++ for examining and manipulating inspanidual characters.

The character-handpng pbrary includes several functions that perform useful tests and manipulations of character data. Each function receives a character, represented as an int, or EOF as an argument. Characters are often manipulated as integers.

Remember that EOF normally has the value –1 and that some hardware architectures do not allow negative values to be stored in char variables. Therefore, the character-handpng functions manipulate characters as integers.

The following table summarizes the functions of the character-handpng pbrary. When using functions from the character-handpng pbrary, include the <cctype> header.

Examples

The following example demonstrates the use of the functions isdigit, isalpha, isalnum and isxdigit. Function isdigit determines whether its argument is a digit (0–9). The function isalpha determines whether its argument is an uppercase letter (A-Z) or a lowercase letter (a–z). The function isalnum determines whether its argument is an uppercase, lowercase letter or a digit. Function isxdigit determines whether its argument is a hexadecimal digit (A–F, a–f, 0–9).

Example 1

void setup () {
   Serial.begin (9600);
   Serial.print ("According to isdigit:
");
   Serial.print (isdigit(  8  ) ? "8 is a": "8 is not a");
   Serial.print (" digit
" );
   Serial.print (isdigit(  8  ) ?"# is a": "# is not a") ;
   Serial.print (" digit
");
   Serial.print ("
According to isalpha:
" );
   Serial.print (isalpha( A  ) ?"A is a": "A is not a");
   Serial.print (" letter
");
   Serial.print (isalpha( A  ) ?"b is a": "b is not a");
   Serial.print (" letter
");
   Serial.print (isalpha( A ) ?"& is a": "& is not a");
   Serial.print (" letter
");
   Serial.print (isalpha(  A  ) ?"4 is a":"4 is not a");
   Serial.print (" letter
");
   Serial.print ("
According to isalnum:
");
   Serial.print (isalnum(  A  ) ?"A is a" : "A is not a" );

   Serial.print (" digit or a letter
" );
   Serial.print (isalnum(  8  ) ?"8 is a" : "8 is not a" ) ;
   Serial.print (" digit or a letter
");
   Serial.print (isalnum(  #  ) ?"# is a" : "# is not a" );
   Serial.print (" digit or a letter
");
   Serial.print ("
According to isxdigit:
");
   Serial.print (isxdigit(  F  ) ?"F is a" : "F is not a" );
   Serial.print (" hexadecimal digit
" );
   Serial.print (isxdigit(  J  ) ?"J is a" : "J is not a" ) ;
   Serial.print (" hexadecimal digit
" );
   Serial.print (isxdigit(  7  ) ?"7 is a" : "7 is not a" ) ;

   Serial.print (" hexadecimal digit
" );
   Serial.print (isxdigit(  $  ) ? "$ is a" : "$ is not a" );
   Serial.print (" hexadecimal digit
" );
   Serial.print (isxdigit(  f  ) ? “f is a" : "f is not a");
   
}

void loop () {

}

Result

According to isdigit:
8 is a digit
# is not a digit
According to isalpha:
A is a letter
b is a letter
& is not a letter
4 is not a letter
According to isalnum:
A is a digit or a letter

8 is a digit or a letter
# is not a digit or a letter
According to isxdigit:
F is a hexadecimal digit
J is not a hexadecimal digit
7 is a hexadecimal digit

$ is not a hexadecimal digit
f is a hexadecimal digit

We use the conditional operator (?:) with each function to determine whether the string " is a " or the string " is not a " should be printed in the output for each character tested. For example, pne a indicates that if 8 is a digit—i.e., if isdigit returns a true (nonzero) value—the string "8 is a " is printed. If 8 is not a digit (i.e., if isdigit returns 0), the string " 8 is not a " is printed.

Example 2

The following example demonstrates the use of the functions islower and isupper. The function islower determines whether its argument is a lowercase letter (a–z). Function isupper determines whether its argument is an uppercase letter (A–Z).

int thisChar = 0xA0;

void setup () {
   Serial.begin (9600);
   Serial.print ("According to islower:
") ;
   Serial.print (islower(  p  ) ? "p is a" : "p is not a" );
   Serial.print ( " lowercase letter
" );
   Serial.print ( islower(  P ) ? "P is a" : "P is not a") ;
   Serial.print ("lowercase letter
");
   Serial.print (islower(  5  ) ? "5 is a" : "5 is not a" );
   Serial.print ( " lowercase letter
" );
   Serial.print ( islower(  !  )? "! is a" : "! is not a") ;
   Serial.print ("lowercase letter
");

   Serial.print ("
According to isupper:
") ;
   Serial.print (isupper (  D  ) ? "D is a" : "D is not an" );
   Serial.print ( " uppercase letter
" );
   Serial.print ( isupper (  d  )? "d is a" : "d is not an") ;
   Serial.print ( " uppercase letter
" );
   Serial.print (isupper (  8  ) ? "8 is a" : "8 is not an" );
   Serial.print ( " uppercase letter
" );
   Serial.print ( islower(  $  )? "$ is a" : "$ is not an") ;
   Serial.print ("uppercase letter
 ");
}

void setup () {

}

Result

According to islower:
p is a lowercase letter
P is not a lowercase letter
5 is not a lowercase letter
! is not a lowercase letter

According to isupper:
D is an uppercase letter
d is not an uppercase letter
8 is not an uppercase letter
$ is not an uppercase letter

Example 3

The following example demonstrates the use of functions isspace, iscntrl, ispunct, isprint and isgraph.

The function isspace determines whether its argument is a white-space character, such as space ( ), form feed ( f ), newpne ( ), carriage return ( ), horizontal tab ( ) or vertical tab ( v ).

The function iscntrl determines whether its argument is a control character such as horizontal tab ( ), vertical tab ( v ), form feed ( f ), alert ( a ), backspace (  ), carriage return ( ) or newpne ( ).

The function ispunct determines whether its argument is a printing character other than a space, digit or letter, such as $, #, (, ), [, ], {, }, ;, : or %.

The function isprint determines whether its argument is a character that can be displayed on the screen (including the space character).

The function isgraph tests for the same characters as isprint, but the space character is not included.

void setup () {
   Serial.begin (9600);
   Serial.print ( " According to isspace:
Newpne ") ;
   Serial.print (isspace(  
  )? " is a" : " is not a" );
   Serial.print ( " whitespace character
Horizontal tab") ;
   Serial.print (isspace(  	  )? " is a" : " is not a" );
   Serial.print ( " whitespace character
") ;
   Serial.print (isspace( % )? " % is a" : " % is not a" );
   
   Serial.print ( " 
According to iscntrl:
Newpne") ;
   Serial.print ( iscntrl(  
  )?"is a" : " is not a" ) ;
   Serial.print (" control character
");
   Serial.print (iscntrl(  $  ) ? " $ is a" : " $ is not a" );
   Serial.print (" control character
");
   Serial.print ("
According to ispunct:
");
   Serial.print (ispunct( ;  ) ?"; is a" : "; is not a" ) ;
   Serial.print (" punctuation character
");
   Serial.print (ispunct( Y  ) ?"Y is a" : "Y is not a" ) ;
   Serial.print ("punctuation character
");
   Serial.print (ispunct( #  ) ?"# is a" : "# is not a" ) ;
   Serial.print ("punctuation character
");

   Serial.print ( "
 According to isprint:
");
   Serial.print (isprint( $  ) ?"$ is a" : "$ is not a" );
   Serial.print (" printing character
Alert ");
   Serial.print (isprint( a  ) ?" is a" : " is not a" );
   Serial.print (" printing character
Space ");
   Serial.print (isprint(    ) ?" is a" : " is not a" );
   Serial.print (" printing character
");
   
   Serial.print ("
 According to isgraph:
");
   Serial.print (isgraph ( Q  ) ?"Q is a" : "Q is not a" );
   Serial.print ("printing character other than a space
Space ");
   Serial.print (isgraph (   ) ?" is a" : " is not a" );
   Serial.print ("printing character other than a space ");
}

void loop () {

}

Result

According to isspace:
Newpne is a whitespace character
Horizontal tab is a whitespace character
% is not a whitespace character
According to iscntrl:
Newpne is a control character
$ is not a control character
According to ispunct:
; is a punctuation character
Y is not a punctuation character
# is a punctuation character
According to isprint:
$ is a printing character
Alert is not a printing character
Space is a printing character
According to isgraph:
Q is a printing character other than a space
Space is not a printing character other than a space