Win32::API returns 1 character when reading a VB DLL

rpnoble has asked for the wisdom of the Perl Monks concerning the following question:

Here is my code:

use Win32::API;
#setup DLL
$PGetAddress = Win32::API->new('IBKGetAddress2.dll', 'GetAddress', 'PP
+', 'P');
if(not defined $PGetAddress) 
{
    die "Can't import API : $!\n";
}

$Address="419 w 154";
$ZipCode="10032";

$return=$PGetAddress->Call($Address,$ZipCode)||die "Can't run API $!\n
+";;

print "Output: $return\n"; 
print "Output Length: ".length($return)."\n";
[download]

Runing AS Perl 5.8.6.
The return from the VB DLL is a 1000 character string with a valid US Postal address. However I can only read the first letter of the return string. Do I need to Pack and Unpack? Not sure how to continue. Thanks for the help.

Comment on Win32::API returns 1 character when reading a VB DLL Download Code

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Re: Win32::API returns 1 character when reading a VB DLL ("UNICODE") by tye (Sage) on Jul 22, 2005 at 14:44 UTC
Win32::API's "P" will copy the "string" up to the first '\0'. It sounds like you have a (what Microsoft calls) "UNICODE" string (16-bit characters), so you've got something like "s\0t\0r\0i\0n\0g\0\0\0". So you can't use Win32::API's "P" since then only "s\0" gets copied. But if that is the case, then you are probably supposed to pass in 16-bit-character strings as well. Which means something similar to (I can't really test this since I don't have your .dll): `#!/usr/bin/perl -w use strict; use Win32::API; my $PGetAddress = Win32::API->new( 'IBKGetAddress2.dll', 'GetAddress', 'PP', 'N' ) or die "Can't import API : $!\n"; my $Address = pack "S", unpack("C","419 w 154"), 0; my $ZipCode = pack "S", unpack("C","10032"), 0; my $return = $PGetAddress->Call( $Address, $ZipCode ) or die "Can't run API: $! ($^E)\n"; my $string = pack "C", unpack "S", unpack "P2000", pack "L", $return +; $string =~ s/\0.//s; print "Output: ($string)\n";` [download] If you've got a variable-length output string, then things get really ugly. But this is all just guessing. Oh, and by way of explanation, the first two strings of pack/unpack convert 8-bit-character strings into 16-bit-character strings. The last string of pack/unpack goes like this: Make what looks like a C struct containing the pointer that was returned: pack "L", $return; Copy into a Perl string the 2000 bytes which that pointer points to: unpack "P2000", Get the list of numbers from treating each pair of bytes (16 bits) as a number: unpack "S", Build a string from those numbers: my $string = pack "C", Remove the terminating '\0' and anything after it: $string =~ s/\0.*//s; - tye	[reply] [d/l]

Replies are listed 'Best First'.

Re: Win32::API returns 1 character when reading a VB DLL ("UNICODE")
by tye (Sage) on Jul 22, 2005 at 14:44 UTC

Win32::API's "P" will copy the "string" up to the first '\0'. It sounds like you have a (what Microsoft calls) "UNICODE" string (16-bit characters), so you've got something like "s\0t\0r\0i\0n\0g\0\0\0". So you can't use Win32::API's "P" since then only "s\0" gets copied.

But if that is the case, then you are probably supposed to pass in 16-bit-character strings as well. Which means something similar to (I can't really test this since I don't have your *.dll):

#!/usr/bin/perl -w
use strict;

use Win32::API;

my $PGetAddress = Win32::API->new(
        'IBKGetAddress2.dll', 'GetAddress', 'PP', 'N' )
    or  die "Can't import API : $!\n";

my $Address = pack "S*", unpack("C*","419 w 154"), 0;
my $ZipCode = pack "S*", unpack("C*","10032"), 0;

my $return = $PGetAddress->Call( $Address, $ZipCode )
    or  die "Can't run API: $! ($^E)\n";

my $string = pack "C*", unpack "S*", unpack "P2000", pack "L", $return
+;
$string =~ s/\0.*//s;

print "Output: ($string)\n";
[download]

If you've got a variable-length output string, then things get really ugly.

But this is all just guessing.

Oh, and by way of explanation, the first two strings of pack/unpack convert 8-bit-character strings into 16-bit-character strings. The last string of pack/unpack goes like this:

Make what looks like a C struct containing the pointer that was returned:
pack "L", $return;
Copy into a Perl string the 2000 bytes which that pointer points to:
unpack "P2000",
Get the list of numbers from treating each pair of bytes (16 bits) as a number:
unpack "S*",
Build a string from those numbers:
my $string = pack "C*",
Remove the terminating '\0' and anything after it:
$string =~ s/\0.*//s;

- tye

[reply]
[d/l]