Run desktop app Lost connection to device.

[GavinDon]

run windows . flutter calls the DLL, and already gets the value returned by c. But then it will lose connection to device.
I don't know what's causing this.Below is my code
` Future sendAPDUHex(String cmd) async {
int sendLen = cmd.length ~/ 2;
try {

  Pointer<Uint8> apduRLen = calloc.allocate(sizeOf<Uint8>());

  Pointer<Uint8> apduResData = calloc.allocate(sizeOf<Uint8>());

  Pointer<ffi.Utf8> sendData = cmd.toNativeUtf8();

  int apduRst =
      await cpuAPDUHexFun(icDev, sendLen, sendData, apduRLen, apduResData);
  debugPrint("apduRst=$apduRst");
  if (apduRst != 0) {
    return "";
  }
  Pointer<ffi.Utf8> dataFromAddress =
      Pointer.fromAddress(apduResData.address);
  String message = dataFromAddress.toDartString();
  debugPrint("message=$message");
  await Future.microtask(() => calloc.free(apduRLen));
  await Future.microtask(() => calloc.free(apduResData));
  await Future.microtask(() => calloc.free(dataFromAddress));
  return message;
} on ArgumentError catch (e) {
  return e.toString();
} on Exception catch (e) {
  return e.toString();
}

}`

[dcharkes]

But then it will lose connection to device.

Any segfault would cause this. For example reading memory that has been freed, or double free.

Add prints to figure out till where it works.

debugPrint("apduRst=$apduRst");

This print still succeeds?

You can use .address to see what memory you're trying to access.

Side note:

calloc.allocate(sizeOf<Uint8>());

Use calloc<Uint8>() instead, sizeOf will be automatic.

Side note 2:

await Future.microtask(() => calloc.free(apduRLen));

Use calloc.free(apduRLen). FFI calls are fast, no need to use async here.

Side note 3:

Instead of manual frees, you can use the Arena:

https://github.com/dart-lang/ffi/blob/master/lib/src/arena.dart

[GavinDon]

The modification according to the above three points will still lose.

The printing is normal. I don't know if it is a memory allocation problem. Sometimes the first time it is normal, the second time it runs, it will lose