PDevMode and DocumentProperties. Error when Migrating between Delphi 7+XE - delphi

Question

I have the following function below that gathers the document properties of a PDF that I am printing.
For some reason, in Delphi 7 (running XP), this works great...however, when I try to recompile with Delphi XE using Windows 7, the function always seems to exit failing...dwRet = IDOK!
I noticed that my dwNeeded object in Delphi 7 was 7332, and in XE it is 4294967295!!
Any idea how I can quickly fix this?
Function TPrintPDF.GetPrinterDevMode ( pDevice: PChar ): PDevMode;
Var
pDevModeVar : PDevMode;
pDevModeVar2 : PDevMode;
dwNeeded : DWord;
dwRet : DWord;
Begin
{ Start by opening the printer }
If (Not OpenPrinter (pDevice, PrinterHandle, Nil))
Then Result := Nil;
{ Step 1: Allocate a buffer of the correct size }
dwNeeded := DocumentProperties (0,
PrinterHandle, { Handle to our printer }
pDevice, { Name of the printer }
pDevModevar^, { Asking for size, so these are not used }
pDevModeVar^,
0); { Zero returns buffer size }
GetMem (pDevModeVar, dwNeeded);
{ Step 2: Get the default DevMode for the printer }
dwRet := DocumentProperties (0,
PrinterHandle,
pDevice,
pDevModeVar^, { The address of the buffer to fill }
pDevModeVar2^, { Not using the input buffer }
DM_OUT_BUFFER); { Have the output buffer filled }
{ If failure, cleanup and return failure }
If (dwRet <> IDOK) Then Begin
FreeMem (pDevModeVar);
ClosePrinter (PrinterHandle);
Result := Nil;
End;
{ Finished with the printer }
ClosePrinter (PrinterHandle);
{ Return the DevMode structure }
Result := pDevModeVar;
End; { GetPrinterDevMode Function }

Answer 1

Here are the problems that I can see with your code:
The return value of DocumentProperties is a signed 32 bit integer. It's declared as LONG. A negative value means an error occurred and that's what's happening to you. Only you don't see the negative value because you've stuffed the value into an unsigned integer. Unfortunately XE fails to declare LONG. So change your code to use Integer instead.
You don't check for errors when DocumentProperties returns. If an error occurs, a negative value is returned. Make sure you check for that.
You are passing random garbage in the 4th and 5th parameters to DocumentProperties. I suspect that you can pass nil for both parameters the first time that you call DocumentProperties. You can certainly pass nil for the 5th parameter both times you call the function since you never set DM_IN_BUFFER.
When errors occur you set Result to nil, but you continue executing the rest of the function. Don't do that. Call exit to break out of the function. Assigning to Result does not terminate execution in the way that return does in C-like languages does.
Use a try/finally block to ensure that you call CloseHandle. That allows you to write CloseHandle once only.

Answer 2

Here's the solution that David suggested...Thanks David!
{ ---------------------------------------------------------------------------- }
Function TPrintPDF.GetPrinterDevMode ( pDevice: PChar ): PDevMode;
Var
pDevModeVar : PDevMode;
pDevModeVar2 : PDevMode;
dwNeeded : Long64;
dwRet : Long64;
Begin
Result := Nil;
{ Start by opening the printer }
If (OpenPrinter (pDevice, PrinterHandle, Nil)) Then Begin
Try
{ Step 1: Allocate a buffer of the correct size }
dwNeeded := DocumentProperties (0,
PrinterHandle, { Handle to our printer }
pDevice, { Name of the printer }
Nil, { Asking for size, so these are not used }
Nil,
0); { Zero returns buffer size }
{ Exit if this fails }
If (dwNeeded < 0)
Then Exit;
GetMem (pDevModeVar, dwNeeded);
{ Step 2: Get the default DevMode for the printer }
dwRet := DocumentProperties (0,
PrinterHandle,
pDevice,
pDevModeVar^, { The address of the buffer to fill }
pDevModeVar2^, { Not using the input buffer }
DM_OUT_BUFFER); { Have the output buffer filled }
{ If failure, cleanup and return failure }
If (dwRet <> IDOK) Then Begin
FreeMem (pDevModeVar);
ClosePrinter (PrinterHandle);
Result := Nil;
End;
{ Finished with the printer }
Finally
ClosePrinter (PrinterHandle);
End; { Try }
{ Return the DevMode structure }
Result := pDevModeVar;
End; { If we could open the printer }
End; { GetPrinterDevMode Function }