Delphi-to-C dll: Passing Arrays - c

Question

I'm using Delphi to load a dll (that I created in Delphi XE-3) for the purposes of interfacing with some C code. My problem is figuring out why my arrays aren't being passed to the c functions - they're the only ones not to. The delphi file (simplified) looks like this:
program CallcCode
uses
SysUtils, Windows,
DLLUnit in 'DLLUnit.pas'; // Header conversion
var
DLLHandle: cardinal;
n: Integer;
A: TArray<Integer>;
result1: Integer;
begin
// Initialize each Array
SetLength(A,n);
A[0] = ...;
// Load the DLL (and confirm its loaded)
DLLhandle := LoadLibrary('dllname.dll');
if DLLhandle <> 0 then
begin
result1 := dll_func1(n,A); // A and B are not passed correctly
end
FreeLibrary(DLLHandle);
end.
I successfully "Trace into" dll_func1 the first time, entering DLLUnit, which has:
const
nameofDLL = 'dllname';
function dll_func1(n: Integer; A: TArray<Integer>): Integer; cdecl; external nameofDLL;
"Tracing-into" again, I arrive at the c file, which still has the correct n and DLLdefs values, but A (under the "Local Variables" heading) has become:
[-] A :(Aplha-Numeric)
..[0] 0 (0x00000000)
I know that I'm at least accessing the DLL (hopefully) correctly because other function calls work as they should and I am able to trace into the dll_func1.c file without a problem. I tried changing the function to
function dll_func1(n: Integer; A: PInteger): Integer; cdecl; external nameofDLL;
...
result1 := dll_func1(n,PInteger(A))
or
function dll_func1(n: Integer; A: PInteger): Integer; cdecl; external nameofDLL;
...
result1 := dll_func1(n,#A[0])
(using both TArray and array of Integer or A) but there is no change, which leaves me to believe this is related to a problem I'm not seeing. The whole thing compiles and runs, but result1 is incorrect because of the TArray failures. Any ideas on what is going wrong?
EDIT The function in C as:
int dll_func1(int n, int A [])

Answer 1

Your question contains two Delphi declarations for the external function. One of them uses TArray<T> as a parameter. That is completely wrong. Don't do that. You cannot use a Delphi dynamic array as an interop type. The reason being that TArray<T> is a complex managed type that can only be created and consumed by Delphi code.
You need to do as I do below, and as I explained in my answer to your previous question, and declare the array parameter as pointer to element type. For example, PInteger, PDouble, etc.
There's quite a lot of confusion here, and needless complexity. What you need is the simplest possible example that shows how to pass an array from your Delphi code to C code.
Here is is.
C code
//testarray.c
void printDouble(double d); // linker will resolve this from the Delphi code
void test(double *arr, int count)
{
int i;
for (i=0; i<count; i++)
{
printDouble(arr[i]);
}
}
Delphi code
program DelphiToC;
{$APPTYPE CONSOLE}
uses
Crtl;
procedure _printDouble(d: Double); cdecl;
begin
Writeln(d);
end;
procedure test(arr: PDouble; count: Integer); cdecl; external name '_test';
{$L testarray.obj}
var
arr: TArray<Double>;
begin
arr := TArray<Double>.Create(1.0, 2.0, 3.0, 42.0, 666.0);
test(PDouble(arr), Length(arr));
Readln;
end.
Compile the C code using, for example, the Borland C compiler like this:
bcc32 -c testarray.c
And the output is:
1.00000000000000E+0000
2.00000000000000E+0000
3.00000000000000E+0000
4.20000000000000E+0001
6.66000000000000E+0002
Note that I linked to the C code statically because that was easier for me. Nothing much changes if you put the C code in a DLL.
The conclusion is that the code I gave you in my answer to your previous, and that I repeat here, is correct. That approach succeeds in passing an array from Delphi code to C. It looks like your diagnostics and debugging is in error.
You are only inspecting A[0] so it's hardly surprising that you only see one value. If only you would look at A[1], A[2], ... , A[n-1] you would see that that all the values are being passed correctly. Or perhaps your debugging was carried out on the erroneous declaration of the external function that used TArray<T> as a parameter.