John M. Dlugosz has asked for the wisdom of the Perl Monks concerning the following question:

I made several calls to a few Win32 primitives in this file, and all went well. Until I get to this one: The first returns success, but the second complains that the handle is invalid.

Am I importing them wrong, passing it wrong, or what?

######
## try WNetOpenEnum et.al. to find connections w/o letters.

my $WNetOpenEnum= new Win32::API ("mpr", "WNetOpenEnum", "IIIIP", "N")
+ or die;
$handle= 'xxxx';  # allocate 4 bytes
use constant RESOURCE_CONNECTED => 0x00000001;
use constant RESOURCETYPE_DISK => 0x00000001;
$result= $WNetOpenEnum->Call (RESOURCE_CONNECTED, RESOURCETYPE_DISK, 0
+, 0, $handle);
print "result for WNetOpenEnum is $result\n";

my $WNetEnumResource= new Win32::API ("mpr", "WNetEnumResource", "PPPP
+", "I") or die;
my $count= pack ("V", -1);
my $bufsize= 5000;
$buffer= 'x' x (1+$bufsize);
for (;;) {
   $bufsize= pack ("V", 5000);
   $result= $WNetEnumResource->Call ($handle, $count, $buffer, $bufsiz
+e);
   print "result for WNetEnumResource is $result\n";
   last if $result != 0;
   print "count=$count, bufsize=$bufsize\n";
   print $buffer;  # just to see if it's not all x's.
   }

[download]

Replies are listed 'Best First'.
Re: Passing/Returning HANDLE's with Win32::API
by Corion (Patriarch) on Feb 07, 2005 at 22:56 UTC

    I believe your declaration for WNetEnumResource is wrong: The MSDN declares it as

    DWORD WNetEnumResource(
  HANDLE hEnum,
  LPDWORD lpcCount,
  LPVOID lpBuffer,
  LPDWORD lpBufferSize
);

    [download]

    which I interpret as LPPP and not as PPPP. Try it with the following code:

    my $WNetEnumResource= new Win32::API ("mpr", "WNetEnumResource", "VPPP
+", "I") or die;
my $count= pack ("V", -1);
my $bufsize= 5000;
$buffer= 'x' x (1+$bufsize);
for (;;) {
   $bufsize= pack ("V", 5000);
   $result= $WNetEnumResource->Call ($handle, $count, $buffer, $bufsiz
+e);
   print "result for WNetEnumResource is $result\n";
   last if $result != 0;
   print "count=$count, bufsize=$bufsize\n";
   print $buffer;  # just to see if it's not all x's.
   }

    [download]

    Updated: The prototype should have been LPPP, and not VPPP

[reply]
[d/l]
[select]
      Then it tells me that the argument is not numeric. The HANDLE received out of the first function is a 4-byte opaque cookie.
[reply]

        Treat this opaque cookie as a number, that is, unpack it, and then pass it in again:

        $handle = unpack "V", $handle;

....

        [download]
[reply]
[d/l]

Back to Seekers of Perl Wisdom