FindWindowA function does not yield the expected output in dart foreign function interface-CodePudding

The following dart code's expected output is the handle to the file explorer window but the output always comes out to be 0 even though the file explorer window does exist!

import 'package:ffi/ffi.dart';
import 'dart:ffi';

void main() {
  DynamicLibrary dl = DynamicLibrary.open('user32.dll');
  final func = dl.lookupFunction<
      IntPtr Function(Pointer<Utf16>?, Pointer<Utf16>?),
      int Function(Pointer<Utf16>?, Pointer<Utf16>?)
    >('FindWindowA');

  print(func(nullptr, 'File Explorer'.toNativeUtf16()));
}

I have ran the function FindWindowA in a c program and it has returned the exptected output with the same input values that are NULL and 'File Explorer'.

In dart using null throws the error Invalid argument(s): argument value for ':ffi_param1' is null; hence the use of nullptr

CodePudding user response：

FindWindowA does not take pointers to UTF-16 strings. The A in FindWindowA stands for "ANSI", which is Microsoft's way of indicating that it uses strings with single-byte code units encoded in the system's local encoding. (This is also indicated by its signature, which takes LPCSTR arguments.)

If you want to pass UTF-16 strings (which in Microsoft Windows are considered "wide strings"), then use FindWindowW.