encoding::warnings - Warn on implicit encoding conversions


NAME

encoding::warnings - Warn on implicit encoding conversions


VERSION

This document describes version 0.13 of encoding::warnings, released June 20, 2016.


NOTICE

As of Perl 5.26.0, this module has no effect. The internal Perl feature that was used to implement this module has been removed. In recent years, much work has been done on the Perl core to eliminate discrepancies in the treatment of upgraded versus downgraded strings. In addition, the the encoding manpage pragma, which caused many of the problems, is no longer supported. Thus, the warnings this module produced are no longer necessary.

Hence, if you load this module on Perl 5.26.0, you will get one warning that the module is no longer supported; and the module will do nothing thereafter.


SYNOPSIS

    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;


DESCRIPTION

Overview of the problem

By default, there is a fundamental asymmetry in Perl's unicode model: implicit upgrading from byte-strings to unicode-strings assumes that they were encoded in ISO 8859-1 (Latin-1), but unicode-strings are downgraded with UTF-8 encoding. This happens because the first 256 codepoints in Unicode happens to agree with Latin-1.

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.

Detecting the problem

This module simplifies the process of diagnosing such problems. Just put this line on top of your main program:

    use encoding::warnings;

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';

Solving the problem

Most of the time, this warning occurs when a byte-string is concatenated with a unicode-string. There are a number of ways to solve it:


CAVEATS

For Perl 5.9.4 or later, this module's effect is lexical.

For Perl versions prior to 5.9.4, this module affects the whole script, instead of inside its lexical block.


SEE ALSO

the perlunicode manpage, the perluniintro manpage

the open manpage, the utf8 manpage, the encoding manpage, the Encode manpage


AUTHORS

Audrey Tang


COPYRIGHT

Copyright 2004, 2005, 2006, 2007 by Audrey Tang <cpan@audreyt.org>.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

See http://www.perl.com/perl/misc/Artistic.html

 encoding::warnings - Warn on implicit encoding conversions