use encoding::warnings; # or 'FATAL' to raise fatal exceptions utf8::encode($a = chr(20000)); # a byte-string (raw bytes) $b = chr(20000); # a unicode-string (wide characters) # "Bytes implicitly upgraded into wide characters as iso-8859-1" $c = $a . $b;
However, this silent upgrading can easily cause problems, if you happen to mix unicode strings with non-Latin1 data --- i.e. byte-strings encoded in UTF-8 or other encodings. The error will not manifest until the combined string is written to output, at which time it would be impossible to see where did the silent upgrading occur.
Afterwards, implicit upgrading of high-bit bytes will raise a warning. Ex.: "Bytes implicitly upgraded into wide characters as iso-8859-1 at - line 7".
However, strings composed purely of ASCII code points (0x00..0x7F) will not trigger this warning.
You can also make the warnings fatal by importing this module as:
use encoding::warnings 'FATAL';
If your program does not need compatibility for Perl 5.6 and earlier, the recommended approach is to apply appropriate IO disciplines, so all data in your program become unicode-strings. See encoding, open and ``binmode'' in perlfunc for how.
The other way works too, especially if you are sure that all your data are under the same encoding, or if compatibility with older versions of Perl is desired.
You may downgrade strings with "Encode::encode" and "utf8::encode". See Encode and utf8 for details.
If you are confident that all byte-strings will be in a specific encoding like UTF-8, and need not support older versions of Perl, use the "encoding" pragma:
use encoding 'utf8';
Similarly, this will silence warnings from this module, and preserve the default behaviour:
use encoding 'iso-8859-1';
However, note that "use encoding" actually had three distinct effects:
This is similar to what open pragma does.
This turns all literal string in your program into unicode-strings (equivalent to a "use utf8"), by decoding them using the specified encoding.
This will silence warnings from this module, as shown above.
Because literal conversions also work on empty strings, it may surprise some people:
use encoding 'big5'; my $byte_string = pack("C*", 0xA4, 0x40); print length $a; # 2 here. $a .= ""; # concatenating with a unicode string... print length $a; # 1 here!
In other words, do not "use encoding" unless you are certain that the program will not deal with any raw, 8-bit binary data at all.
However, the "Filter => 1" flavor of "use encoding" will not affect implicit upgrading for byte-strings, and is thus incapable of silencing warnings from this module. See encoding for more details.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.