How to acess the result from a function pointer in dart

Question

I am trying to get the return value from c++ function in dart.

My c++ code is something like this

static bool is_alive() {
  return true;
}

From dart, I loaded the shared lib with this native code and I am trying to call that is_alive() function.

typedef BooleanFunction = Pointer<Int8> Function();

Pointer<NativeFunction<BooleanFunction>> isAlive = (functionAddress).cast<NativeFunction<BooleanFunction>>();
Pointer<Int8> Function() isAliveFunc = isAlive.asFunction();

I called then the isAliveFunc from dart and I want the result of that functions. I tried all these ways. None of these works.

Pointer<Int8> casted = isAliveFunc()!.cast();
Pointer<Int8>? fromPointer = isAliveFunc()!;

developer.log('value : $casted');

I get the result like this Pointer<Int8>: address=0x1

How can I fetch the value from this pointer in dart ? I expect to get a 1 or 0 as the result.

Answer 1

For some reason you never actually call your isAliveFunc function.

Just call the function as you would any other:

Pointer<Int8> casted = isAliveFunc();

or

Pointer<Int8> casted = isAliveFunc.call();

You should also be paying attention to your Dart static analysis warnings and errors.

---

Your function definitions are also incorrect. is_alive returns a bool/Int8, not a pointer.

Your BooleanFunction typedef should be:

typedef BooleanFunction = Int8 Function();

int Function() isAliveFunc = isAlive.asFunction();

And the function call return should be assigned to an int:

int casted = isAliveFunc();