However, in my example, the contents of the string passed to encode_utf8 were not code points - there were already in UTF8, and were therefore left unaltered by encode_utf8.

use strict;
use warnings;

use Encode;
use charnames qw(greek);

for ("ABCD", "ABC\N{delta}", "\N{alpha}\N{beta}\N{gamma}\N{delta}") {
    printf "orig len=%d, enc len=%d\n",
    length($_),
    length(Encode::encode_utf8($_));
}
__END__
$ perl /tmp/p
orig len=4, enc len=4
orig len=4, enc len=5
orig len=4, enc len=8
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Regardless of a string's internal coding, Encode::encode_utf8() returns a string consisting of a codepoint for each the octets of what would be the utf8 representation of the original string, ragardless of how that original string was actually stored internally.

Dave.

>No. The string passed to encode_utf8 did contain codepoints; that's what Perl strings are.

Hmm, this doesn't make sense to me: AFAIK Perl strings never store code points, but rather store the UTF-8 encoding of the code points e.g. the string with a Greek uppercase Kappa, whose code point is 039A:

$str = "\x{039A}";
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does not contain, in hex, 039A, but rather in hex, CE9A, the UTF8 encoding of that code point.

>And the function returned something that was different from the original string, as can be seem below:

What your example seems to demonstrate, AFAICS, is the character v. byte o/p of length, when presented with strings where the UTF-8 flag is switched on/off.

So for the final string, containing alpha, beta, gamma, and delta, it has a length of 4 characters, when Perl knows that it contains valid UTF-8, but a length of 8 when Perl is assuming the old byte=character semantics. However, both the strings are byte-for-byte identical.

Or, if I'm wrong here, I'm very confused.

Steve Collyer

Hmm, this doesn't make sense to me: AFAIK Perl strings never store code points, but rather store the UTF-8 encoding of the code points e.g. the string with a Greek uppercase Kappa, whose code point is 039A: $str = "\x{039A}"; does not contain, in hex, 039A, but rather in hex, CE9A, the UTF8 encoding of that code point. /

You are getting diverted by how perl happens internally to store a string. This is almost always completely irrelevant, may change between perl versions, and is just confusing you. $str above is a perl string that contains one character, and ord(that_character) is 0x39a. Whether perl happens to remember that fact by storing the two bytes 0xCE and 0x9A somewhere in memory shouldn't normally concern you.

What your example seems to demonstrate, AFAICS, is the character v. byte o/p of length, when presented with strings where the UTF-8 flag is switched on/off. /

Again, forget the internals, don't worry about the internal UTF8 flag. The length function always returns the number of characters in a string, not the number of bytes.

So for the final string, containing alpha, beta, gamma, and delta, it has a length of 4 characters, when Perl knows that it contains valid UTF-8, but a length of 8 when Perl is assuming the old byte=character semantics. However, both the strings are byte-for-byte identical. /

I don't understand what you are trying to say there.

Perhaps it would help if you viewed the encode_utf8() function as being equivalent the one I include below. Does that make things any clearer? Note that my perl version of this function knows nothing about the internal representation of its arg, or whether it has its UTF8 flag set etc.

sub encode_utf8 {
    my $e;
    for (map ord, split //, $_[0]) {
        if ($_ < 128) {
            $e .= chr($_);
        }
        elsif ($_ < 1024) {
            $e .= chr(0xC0 + ($_ >> 6)); 
            $e .= chr(0x80 + ($_ & 63)); 
        }
        elsif (...)
            ...
        }
    }
    return $e;
}
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Dave.

I'll answer this myself: No, if you give decode_utf8 a string containing octets that are already valid UTF-8, it should return a string byte-for-byte identical but with the UTF-8 flag switched on.

Steve Collyer