Perl Cookbook

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);

Discussion

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 ...