CODEWITHSUNDEEP
pythonarraysdelphipointersctypes
Lorenzo P
Lorenzo P

Reputation: 1540

How do I access wity python ctypes to array values returned with a pointer from a dll coded in Delphi?

I have a Delphi library that is exposing a results with a procedure like this:

procedure Script_GetFindedList(List : Pointer; out Len : Cardinal); stdcall;
var X : TArray<Cardinal>;
begin
  TScriptMethod.Create(SCGetFindedList).SendExecMethod.Free;
  NamedPipe.WaitForReply(Pipe_WaitDelay);
  if not ResultReady then ExitProcess(0);
  SetLength(X,FuncResultStream.Size div 4);
  FuncResultStream.Read(X[0],FuncResultStream.Size);
  Len := Length(X) * 4;
  if Assigned(List) then
    Move(X[0],PByteArray(List)^[0],Len);
end;

And I am able to call it from normal delphi Code like this:

function TFindEngine.GetFindedList : TArray<Cardinal>;
var BufLen : Cardinal;
begin
  Script_GetFindedList(nil, BufLen);
  if BufLen = 0 then Exit;
  SetLength(Result,BufLen div 4);
  Script_GetFindedList(PByteArray(Result), BufLen);
end;

I would like to wrap the code in Python using the ctypes library and I have some code like this:

from ctypes import *

my_dll = windll.Script

def GetFindedList():
    my_dll.Script_GetFindedList.argtypes = [POINTER(c_uint), POINTER(c_uint)]
    my_dll.Script_GetFindedList.restype = None

    BufLen = c_uint()

    my_dll.Script_GetFindedList(None, byref(BufLen))
    if BufLen.value > 0:
        print("BufLen.value : {}".format(BufLen.value))

        ##################################################################
        # alternate solution that just leaks memory while doing nothind
        # buf = array('I', range(BufLen.value))
        # addr, count = buf.buffer_info()
        # Result = cast(addr, POINTER( (c_uint * BufLen.value) ))

        Result = (c_uint * BufLen.value)()

        print("Result before: {}".format(list(Result)))

        my_dll.Script_GetFindedList(byref(Result), byref(BufLen))       
        print("Result after: {}".format(list(Result)))

        return Result
    else:
        return []

But this is not working: I just get the correct BufLen.value but then, with the second call to dll I am not able to populate my array. I did many similar tries, but with no luck. Is there someone that can advise me?

Thank you.

Upvotes: 2

Views: 1981

Answers (1)

David Heffernan
David Heffernan

Reputation: 613013

I'd call it like this:

from ctypes import *
my_dll = windll.Script
my_dll.Script_GetFindedList.restype = None
size = c_uint()
my_dll.Script_GetFindedList(None, byref(size))
result = (c_uint*(size.value//4))()
my_dll.Script_GetFindedList(result, byref(size))
result = list(result)

This function would be much better if you return buffer length rather than size.

I tested this using the following code:

Delphi

library TestDLL;

procedure Script_GetFindedList(List : Pointer; out Len : Cardinal); stdcall;
var
  X: TArray<Cardinal>;
begin
  X := TArray<Cardinal>.Create(1, 2, 3, 4, 5);
  Len := Length(X) * 4;
  if Assigned(List) then
    Move(Pointer(X)^, List^, Len);
end;

exports
  Script_GetFindedList;

begin
end.

Python

from ctypes import *
my_dll = WinDLL(r'full/path/to/TestDLL.dll')
my_dll.Script_GetFindedList.restype = None
size = c_uint()
my_dll.Script_GetFindedList(None, byref(size))
result = (c_uint*(size.value//4))()
my_dll.Script_GetFindedList(result, byref(size))
result = list(result)
print result

Output

[1L, 2L, 3L, 4L, 5L]

Upvotes: 4

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