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Printing Unicode on the Windows Console and the importance of of i/o layers

I wanted to take a look on printing Unicode on the windows console by using the Win32 api and also check how is done in other languages, rather than directly from Perl which hides a lot of details

Problems when wanting to print to the console :

1.The windows console uses an internal buffer that can mangle output

2.Invoking the console using the Unicode switch (cmd.exe /u) does not have an effect

3.Windows supports UTF-16 inherently, not utf8

4.Documentation on Unicode and the console is hard to find.MSDN library, as usual, is a labyrinth with no beginning and end where you can loose track easily

The need arose when I needed to print an old style dos box using the cp437 box drawing characters on the console using their Unicode code points rather than their ASCII representation. The output was mangled/overlapped

Take a look at this pictorial output to get a clear view of the problem

The code that generated the incorrect result is :

#unicode_box_incorrect.pl
use Win32::API;

binmode(STDOUT,':utf8');

#Must set the console code page to UTF8
$SetConsoleOutputCP= new Win32::API( 'kernel32.dll', 'SetConsoleOutputCP', 'N','N' );
$SetConsoleOutputCP->Call(65001);

$line1="\x{2554}".("\x{2550}"x15)."\x{2557}\n";
$line2="\x{2551}".(" "x15)."\x{2551}\n";
$line3="\x{255A}".("\x{2550}"x15)."\x{255D}";
$unicode_string=$line1.$line2.$line3;

print "THIS IS THE INCORRECT EXAMPLE OUTPUT: \n";
print $unicode_string;

Since C++ has a better relationship with Windows than Perl, I did some research on how you can manipulate the console in C++ and used the underlying concepts in Perl.

Fortunately I bumped into illegalargumentexception
who has a fantastic tutorial on the subject using multi-language examples. Also the blog explains various issues on Unicode. great stuff, totally recommended

So the equivalent Perl code would be:

#unicode_box_correct.pl
use Win32::API;
use Encode qw(from_to encode);

#no need to use perlio (in this case) as we are bypassing it through the raw Win32API
#binmode(STDOUT,':utf8');

#Set the console code page to UTF8
$SetConsoleOutputCP= new Win32::API( 'kernel32.dll', 'SetConsoleOutputCP', 'N','N' );
$SetConsoleOutputCP->Call(65001);

#Get a reference to the console STDOUT
$GetStdHandle=new Win32::API( 'kernel32.dll', 'GetStdHandle', 'N', 'N' );
$handle=$GetStdHandle->Call(-11);

#Build dos window
$line1="\x{2554}".("\x{2550}"x15)."\x{2557}\n";
$line2="\x{2551}".(" "x15)."\x{2551}\n";
$line3="\x{255A}".("\x{2550}"x15)."\x{255D}";
$unicode_string=$line1.$line2.$line3;

print "THIS IS THE CORRECT EXAMPLE OUTPUT: \n";
#Force byte semantics because WriteFile API function needs length in bytes not characters
$lengthx=length(Encode::encode_utf8($unicode_string));

#use WriteFile API to treat the Console as a file.WriteConsole won't do it
$WriteFile=new Win32::API( 'kernel32.dll', 'WriteFile', 'NPNNN', 'N' );
$WriteFile->Call($handle,$unicode_string, $lengthx,0,0);


The trick is to use high-level console I/O (WriteFile) rather than low-level console I/O (WriteConsoleOutput) and there is no need to use the WideCharToMultiByte function since Perl uses UTF8 natively while C++ uses 16bit wide chars which need to be converted into multibytes. Note here that Windows treats the wchar as 'real' Unicode while it treats Utf8 as a multibyte encoding, the same as treating ASCII code pages.

Also note that for the example to work, the actual code page of the console does not play a role but the font must be set to Lucida console.
However the Lucida Console font does not support the whole Unicode range, so it does not include all Unicode glyphs.
There is only one issue, how to programmatically set the font on the users' console. This, unfortunately, can only be done on Windows vista and upwards with the SetCurrentConsoleFontEx api function

Ultimately, in pure Perl code without using any Win32 API's (although we still need it for the SetConsoleOutputCP), we turn perio buffering off by using the :unix layer, so it doesn't mess with the console buffer :

#unicode_box_correct_pure_perl.pl
use Win32::API;

binmode(STDOUT, ":unix:utf8");

#Must set the console code page to UTF8
$SetConsoleOutputCP= new Win32::API( 'kernel32.dll', 'SetConsoleOutputCP', 'N','N' );
$SetConsoleOutputCP->Call(65001);

$line1="\x{2554}".("\x{2550}"x15)."\x{2557}\n";
$line2="\x{2551}".(" "x15)."\x{2551}\n";
$line3="\x{255A}".("\x{2550}"x15)."\x{255D}";
$unicode_string=$line1.$line2.$line3;

print "THIS IS THE CORRECT EXAMPLE OUTPUT IN PURE PERL: \n";
print $unicode_string;


Compare this little Perl example with the complexity the other languages have to go through to get to the same result and appreciate Perl's power. magic.

Update:
Better yet,after a chat I had at the Perlmonks forum, the code could be improved by taking out the Win32::API completely and replacing it with Win32::Console :

#unicode_box_correct_pure_perl.pl
binmode(STDOUT, ":unix:utf8");

Win32::Console::OutputCP( 65001 );

$line1="\x{2554}".("\x{2550}"x15)."\x{2557}\n";
$line2="\x{2551}".(" "x15)."\x{2551}\n";
$line3="\x{255A}".("\x{2550}"x15)."\x{255D}";
$unicode_string=$line1.$line2.$line3;

print "THIS IS THE CORRECT EXAMPLE OUTPUT IN PURE PERL: \n";
print $unicode_string;

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