in reply to Low-level version of Win32::API::Struct

My machine is 64 b ... pack('NC',$size,$aKey).
  1. Firstly, template char 'N' is a 32-bit unsigned integer in network (big-endian) order.

    If you are running Windows on Intel (90%+ are), then you would need 'V' which is 32-bit unsigned in VAX (little-endian) order.

  2. But ... as you are on 64-bit OS, if you are running a 64-bit perl: (you don't say?)

    Then size_t will equate to a 64-bit unsigned int which would be template 'Q'.

The simplest template would be 'J' which should work for 32-bit or 64-bit. (Excepting 32-bit perl's compiled for 64-bit ints.)

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Re^2: Low-level version of Win32::API::Struct
by sgv_81 (Novice) on Aug 01, 2012 at 16:21 UTC

    Thank you, I understand that I'm in the wierd option of 32 bit perl for 64 int, Intel and Windows XP (but perl running through Cygwin). I think your post will be very helpful when I make the simplified example from my previous post work and I move into the original problem.

    As a quick refresh, the simplified example from my previous post: 

        #### import an API that uses this structure
    my $getCursor = new Win32::API('user32', 'GetCursorPos','S','N');
    
    #### create a 'POINT' object
    $lpPoint=pack('LL',0,0);
    #### call the function passing our structure object
    $getCursor->Call($lpPoint);
    
    #### and now, access its members
    my ($x,$y) = unpack('LL',$pt);
    print "The cursor is at: ".$x.", ".$y."\n";

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    No matter which parameter I use within pack ('J','L','N','Q' or 'V') in $lpPoint=pack('LL',0,0); I still get the error "Can't call method Pack on a undefined value". The error pops up in $getCursor->Call($lpPoint);.

    From CPAN doc on Win32::API seems that I can substitute the Win32::API::Struct for the packed variable and then pass it to the Win32::API object. Any idea what I'm missing?

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      That is not an example from the docs. 

          my $getCursor = new Win32::API('user32', 'GetCursorPos','S','N');

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      should be 
          my $getCursor = new Win32::API('user32', 'GetCursorPos','P','N');

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      since $lpPoint is a scalar string formally. 'S'/'T' are only for ::Struct objects. The result of pack() is a scalar string. Not a blessed object. If you had a newer version of ::API, you would get a proper croak message 
                              croak("Win32::API::Call: parameter %d must be 
+a%s",  i+1, " Win32::API::Struct object!\n");

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      much better than 0.68 blindly doing ->Pack() on whatever scalar happens to fall in as argument which is what is happening in your case.
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