C is An unsigned char (octet,8bit) value.
W An unsigned char value (can be greater than 255).

So, why "C" values could become greater than 255?

#unpack "C*", $unicode_string.$unicode_string;
#("UNSIGNED OCTETS(C*) ", 12354, 12354)

this seems strange...

Do you mean my example should use "W" for unpack? If so, Does this make sense? The result is same with my machine. My point is, @bytes is not bytes, it is decimal code points for "HIRAGANA LETTER A".

    $code_point=0x3042;#HIRAGANA LETTER A
    $unicode_string=pack('U*', $code_point);
    @bytes=unpack("W*", $unicode_string);
    print join('|', @bytes), "\n";  #==>these are not bytes ,but array
+ of codepoints


    $code_point=0x3042;#HIRAGANA LETTER A
    $unicode_string=pack('U*', $code_point);
    @bytes=map{ sprintf("%X",$_) } unpack("W*", Encode::encode('utf8',
+$unicode_string));
    print join('|', @bytes), "\n";
[download]

update:
I met description of perlunicode:

" pack("C") and unpack("C") are methods for emulating byte-oriented chr() and ord() on Unicode strings. While these methods reveal the internal encoding of Unicode strings, that is not something one normally needs to care about at all."

# this is wrong
@bytes=unpack("C*", $unicode_string); 

# this is right
@byets= unpack("C*", Encode::encode('utf8',$unicode_string));
[download]

So, why "C" values could become greater than 255? this seems strange...

Its all strange to me, I'm not joking

From http://perldoc.perl.org/5.14.1/functions/pack.html

Pack and unpack can operate in two modes: character mode (C0 mode) where the packed string is processed per character, and UTF-8 mode (U0 mode) where the packed string is processed in its UTF-8-encoded Unicode form on a byte-by-byte basis. Character mode is the default unless the format string starts with U . You can always switch mode mid-format with an explicit C0 or U0 in the format. This mode remains in effect until the next mode change, or until the end of the () group it (directly) applies to.

Using C0 to get Unicode characters while using U0 to get non-Unicode bytes is not necessarily obvious. Probably only the first of these is what you want:

...

Those examples also illustrate that you should not try to use pack/unpack as a substitute for the Encode module.

So trying that I get

dd "UNSIGNED OCTETS(C*) ", unpack "C0C*", $unicode_string.$unicode_str
+ing;
dd "UNSIGNED OCTETS(C*) ", unpack "U0C*", $unicode_string.$unicode_str
+ing;
__END__
("UNSIGNED OCTETS(C*) ", 12354, 12354)
("UNSIGNED OCTETS(C*) ", 227, 129, 130, 227, 129, 130)
[download]

So, yes, I think I agree, its a mistake , in that it should probably say You can find the bytes that make up a UTF-8 sequence with:

@bytes = unpack("U0C*", $Unicode_string);
[download]

And this seems to confirm that

    $code_point=0x3042;#HIRAGANA LETTER A
    $unicode_string=pack('U*', $code_point);
    @bytes=map{ sprintf("%X",$_) } unpack("U0C*", $unicode_string);
    print join('|', @bytes), "\n";
__END__
E3|81|82
[download]

update: It says in another part of perluniintro

One way of peeking inside the internal encoding of Unicode characters is to use unpack("C*", ... to get the bytes of whatever the string encoding happens to be, or unpack("U0..", ...) to get the bytes of the UTF-8 encoding:

So yeah, whatever perl's actual internal format that we shouldn't care about is, it is not utf8, and if you want the UTF8 bytes, you need U0C*, otherwise (it looks like) you get IV bytes

Thanks! thanks for your reply!


This code and your explanation is what I was looking for.

@bytes = unpack("U0C*", $Unicode_string);
[download]

In perluniintro, C0 and U0 prefix was mentioned several times, but I didn't understand them without explanation like you did.

It seems you saved me from confusion and from piles of printed pod papers.

I would like to keep reading unicode and pack documents.
Again, thanks for your patience.