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1.4. Converting Between ASCII Characters and Values


You want to print out the number represented by a given ASCII character, or you want to print out an ASCII character given a number.


Use ord to convert a character to a number, or use chr to convert a number to a character:

$num  = ord($char);
$char = chr($num);

The %c format used in printf and sprintf also converts a number to a character:

$char = sprintf("%c", $num);                # slower than chr($num)
printf("Number %d is character %c\n", $num, $num);

Number 101 is character e

A C* template used with pack and unpack can quickly convert many characters.

@ASCII = unpack("C*", $string);
$STRING = pack("C*", @ascii);


Unlike low-level, typeless languages like assembler, Perl doesn't treat characters and numbers interchangeably; it treats strings and numbers interchangeably. That means you can't just assign characters and numbers back and forth. Perl provides Pascal's chr and ord to convert between a character and its corresponding ordinal value:

$ascii_value = ord("e");    # now 101
$character   = chr(101);    # now "e"

If you already have a character, it's really represented as a string of length one, so just print it out directly using print or the %s format in printf and sprintf . The %c format forces printf or sprintf to convert a number into a character; it's not used for printing a character that's already in character format (that is, a string).

printf("Number %d is character %c\n", 101, 101);

The pack , unpack , chr , and ord functions are all faster than sprintf . Here are pack and unpack in action:

@ascii_character_numbers = unpack("C*", "sample");
print "@ascii_character_numbers\n";

115 97 109 112 108 101

$word = pack("C*", @ascii_character_numbers);
$word = pack("C*", 115, 97, 109, 112, 108, 101);   # same
print "$word\n";


Here's how to convert from HAL to IBM:

$hal = "HAL";
@ascii = unpack("C*", $hal);
foreach $val (@ascii) {
    $val++;                 # add one to each ASCII value
$ibm = pack("C*", @ascii);
print "$ibm\n";             # prints "IBM"

The ord function can return numbers from 0 to 255. These correspond to C's unsigned char data type.

See Also

The chr , ord , printf , sprintf , pack , and unpack functions in perlfunc (1) and Chapter 3 of Programming Perl

Previous: 1.3. Exchanging Values Without Using Temporary Variables Perl Cookbook Next: 1.5. Processing a String One Character at a Time
1.3. Exchanging Values Without Using Temporary Variables Book Index 1.5. Processing a String One Character at a Time