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1.4. Converting Between Characters and Values

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

1.4.2. Solution

Use ord to convert a
character to a number, or use chr to convert a
number to its corresponding 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 8-bit bytes;
similarly, use U* for Unicode characters.

@bytes = unpack("C*", $string);
$string = pack("C*", @bytes);
$unistr = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
@unichars = unpack("U*", $unistr);

1.4.3. Discussion

Unlike low-level,
typeless languages such as 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:

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

On single-byte character data, such as plain old ASCII or any of the
various ISO 8859 charsets, the ord function
returns numbers from 0 to 255. These correspond to C's
unsigned char data type.

However, Perl understands more than that: it also has integrated
support for Unicode, the universal character encoding. If you pass
chr, sprintf "%c", or
pack "U*" numeric values greater than 255, the
return result will be a Unicode string.

Here are similar operations with Unicode:

@unicode_points = unpack("U*", "fac\x{0327}ade");
print "@unicode_points\n";
102 97 99 807 97 100 101
$word = pack("U*", @unicode_points);
print "$word\n";
façade

If all you're doing is printing out the characters' values, you
probably don't even need to use unpack. Perl's
printf and sprintf functions
understand a v modifier that works like this:

printf "%vd\n", "fac\x{0327}ade";
102.97.99.807.97.100.101
printf "%vx\n", "fac\x{0327}ade";
66.61.63.327.61.64.65

The numeric value of each character (that is, its "code point" in
Unicode parlance) in the string is emitted with a dot separator.

1.4.4. See Also

The
chr, ord,
printf, sprintf,
pack, and unpack functions in
perlfunc(1) and Chapter 29 of
Programming Perl

1.3. Exchanging Values Without Using Temporary Variables		1.5. Using Named Unicode Characters

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