Setting up Delphi to call a 2 dimensional array in C++ DLL - c++

Question

UPDATED USING PREVIOUS ANSWERS
I have a DLL with the following header definitions:
typedef struct {
int32_t dimSizes[2];
double NumericControl[1];
} DoubleArrayBase;
typedef DoubleArrayBase **DoubleArray;
void __stdcall ReadTERFCorrectedData(char FilepathString[],
int32_t ArrayLengths[], DoubleArray *AmplitudeData,
DoubleArray *FrequencyData, int32_t len);
DoubleArray __cdecl AllocateDoubleArray (int32 *dimSizeArr);
MgErr __cdecl ResizeDoubleArray (DoubleArray *hdlPtr, int32 *dimSizeArr);
MgErr __cdecl DeAllocateDoubleArray (DoubleArray *hdlPtr);
My question is, how do I go about setting up a Delphi call to this function?
My Delphi definition of the call is as follows:
type
PDoubleArray = ^DoubleArray;
DoubleArray = ^PDoubleArrayBase;
PDoubleArrayBase = ^DoubleArrayBase;
DoubleArrayBase = packed record
dimSizes: array[0..1] of Int32;
NumericControl: array[0..0] of Double;
end;
procedure ReadTERFCorrectedData(FilepathString: PAnsiChar;
var ArrayLengths: Int32; AmplitudeData, FrequencyData: PDoubleArray;
len: Int32);stdcall; external DLLDirectory;
function AllocateDoubleArray (SizeArray: PInt): DoubleArray;stdcall; external DLLDirectory;
And then in the body of the code I allocate space for the arrays then get the data as follows:
implementation
{$R *.dfm}
procedure TForm7.btn1Click(Sender: TObject);
var
AmplitudeData, FrequencyData : DoubleArray;
arraylengths: array[0..1] of int32;
I: Integer;
TempSize : Int32;
begin
TempSize := 50;
AmplitudeData := AllocateDoubleArray(#Tempsize);
FrequencyData := AllocateDoubleArray(#Tempsize);
ReadTERFCorrectedData(fileloc, ArrayLengths[0], #AmplitudeData, #FrequencyData, 50);
ShowMessage(arraylengths[1].tostring);
end;
How do I go about accessing the data stored in the AmplitudeData and FrequencyData? They are both DoubleArray types, but how do i get to the DoubleArrayBase.dimSizes and DoubleArrayBase.NumericControl values buried by the pointer? I have tried AmplitudeData[0,0], AmplitudeData.NumericControl, etc but can not get to the values.
I am basically trying to create a Delphi version of what is being done in this post:
https://lavag.org/topic/20486-lv-dll-creates-mysterious-doublearray-class/

Answer 1

The DLL is using fixed-length arrays, but your Delphi code is using dynamic arrays instead. They are not the same thing.
Also, the DLL is expecting a pointer-to-pointer-to-struct, but you are using a pointer-to-record instead. You are missing a level of indirection.
Also, the DLL expects a pointer to a null-terminated AnsiChar C string, not an AnsiString.
Try this instead:
type
PDoubleArray = ^DoubleArray;
DoubleArray = ^PDoubleArrayBase;
PDoubleArrayBase = ^DoubleArrayBase;
DoubleArrayBase = packed record
dimSizes: array[0..1] of Int32;
NumericControl: array[0..0] of Double;
end;
procedure ReadTERFCorrectedData(FilepathString: PAnsiChar;
ArrayLengths: PInt32; AmplitudeData, FrequencyData: PDoubleArray;
len: Int32); stdcall; external '...';
// Alternatively:
//
// procedure ReadTERFCorrectedData(FilepathString: PAnsiChar;
// var ArrayLengths: Int32; var AmplitudeData, FrequencyData: DoubleArray;
// len: Int32); stdcall; external '...';
UPDATE: the function takes DoubleArray* parameters, ie a pointer to a DoubleArray. So you likely need to call it something like this:
procedure TForm7.btn1Click(Sender: TObject);
var
AmplitudeData, FrequencyData : DoubleArray;
ArrayLengths: array[0..1] of Int32;
I: Integer;
begin
ReadTERFCorrectedData(fileloc, #ArrayLengths[0], #AmplitudeData, #FrequencyData, 500);
...
end;
But, there is simply not enough information presented to know whether you need to pre-allocate the arrays before calling the function, or if the function will allocate the arrays for you. The use of pointer-to-pointer indirections strongly implies that the DLL will perform the allocations for you. But what the DoubleArray contents will look like upon exit is anyone's guess without seeing documentation or example C code.
UPDATE: based on the information presented on this page, try something like the following:
procedure DisplayDoubleArray(const Arr: DoubleArray);
var
P: PDouble;
I, Num: Integer;
begin
if (Arr = nil) or (Arr^ = nil) then Exit;
ShowMessage('Arr.dimSizes[0]: ' + Arr^^.dimSizes[0].ToString);
ShowMessage('Arr.dimSizes[1]: ' + Arr^^.dimSizes[1].ToString);
Num := Arr^^.dimSizes[0] * Arr^^.dimSizes[1];
P := #(Arr^^.NumericControl[0]);
for I := 0 to Num-1 do
begin
ShowMessage('Arr.NumericControl[' + I.ToString + ']: ' + P^.ToString);
Inc(P);
end;
end;
procedure TForm7.btn1Click(Sender: TObject);
var
AmplitudeData, FrequencyData : DoubleArray;
ArrayLengths: array[0..1] of Int32;
I: Integer;
begin
ReadTERFCorrectedData(fileloc, #ArrayLengths[0], #AmplitudeData, #FrequencyData, 500);
try
ShowMessage('ArrayLengths[0]: ' + ArrayLengths[0].ToString);
ShowMessage('ArrayLengths[1]: ' + ArrayLengths[1].ToString);
DisplayDoubleArray(AmplitudeData);
DisplayDoubleArray(FrequencyData);
finally
DeAllocateDoubleArray(#AmplitudeData);
DeAllocateDoubleArray(#FrequencyData);
end;
end;