Converting Between ASCII Characters and Values

Problem

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.

Solution

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"; sample

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.