Su, Yu (Eugene) <>  wrote:
>  Hi,
>  
>  I have a DLL from FTDI (ftd2xx.dll www.ftdichip.com) for a USB
>  device. I try to write a simple perl script to list a number of (FTD)
>  USB devices connected to a PC. My code below got an error on invalid
>  parameter;   
>  
>  Argument "M-\0\0\0\0\" isn't numeric in subroutine entry at demo.pl
>  line # 
>  
>  I guess I did not pass a hex data in the function call properly. Can
>  someone help me? 
>  
>  Thanks.
>  
>  Eugene
>  
>  ######## code snippet #######
>  
>  use strict;
>  use Win32::API;
>  use Carp;
>  use warnings;
>  
>  # from FTD2xx programmer guide:
>  # FT_ListDevices(PVOID numDevs,PVOID NULL,DWORD FT_LIST_NUMBER_ONLY)
>     # FT_LIST_NUMBER_ONLY is defined in FTD2xx.h as #define
>  FT_LIST_NUMBER_ONLY = 0x80000000 # my $function = new
>  Win32::API("ftd2xx", "FT_ListDevices", "PPN", "N"); if (not defined
>  $function) { die "Can't import API FT_ListDevices: $!\n"; } my
>  $DevBuffer = " " x 80; my $FT_LIST_NUMBER_ONLY=pack('N', 0x80000000);
>  my $status=$function->Call($DevBuffer,0,$FT_LIST_NUMBER_ONLY);     
>  print "status: $status\n";
>  print "DeviceNumber: $DevBuffer";

I think that you problem is the 'pack'. Why do you think you need it?.
Just use 0x80000000 in your function call, or if you want to define it
as a constant, 'use constant FT_LIST_NUMBER_ONLY =>  0x80000000;' is more
nearly equivalent to the #define you quote, and will add to your codes
readability. For example, you dould write it something like this:

use strict;
use warnings;
use Win32::API;

use constant FT_LIST_NUMBER_ONLY =>  0x80000000;

my $function = new Win32::API("ftd2xx", "FT_ListDevices", "PPN", "N");
die "Can't import API FT_ListDevices: $!\n" unless defined $function;
my $DevBuffer = " " x 80;
my $status=$function-> Call($DevBuffer, 0 ,FT_LIST_NUMBER_ONLY);
print "status: $status\n";
print "DeviceNumber: $DevBuffer";

HTH

-- 
Brian Raven 
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