Binding to C native code with dart:ffi: pass strings to C

[alopez]

Hi,
I am trying to do my first plugin using a native c library but I don't know how to pass a string to a native c function. I have seen this dart example that use Utf8 Class but It doesn't exist in flutter.

import 'package:ffi/ffi.dart';
import 'dart:io' show Platform;

// C string parameter pointer function - char *reverse(char *str, int length);
typedef reverse_func = Pointer<Utf8> Function(Pointer<Utf8> str, Int32 length);
typedef Reverse = Pointer<Utf8> Function(Pointer<Utf8> str, int length);



main() {
  var path = './structs_library/libstructs.so';
  if (Platform.isMacOS) path = './structs_library/libstructs.dylib';
  if (Platform.isWindows) path = r'structs_library\Debug\structs.dll';
  final dylib = DynamicLibrary.open(path);

  final reversePointer = dylib.lookup<NativeFunction<reverse_func>>('reverse');
  final reverse = reversePointer.asFunction<Reverse>();
  final reversedMessage = Utf8.fromUtf8(reverse(Utf8.toUtf8('backwards'), 9));
  print('$reversedMessage');
}

Could you provide me with an example to pass a string to a native c function? Thanks

[Tim Sneath]

You also need import 'dart:ffi'; to use the Pointer class.

Utf8 is part of the ffi package, so you should be able to use it from Flutter.

[alopez]

Thanks for your reply. At the end it works but I don't know if there is an "easy" way to do it.I added ffi: ^0.1.3 to pubspec.yaml and use the import 'package:ffi/src/utf8.dart'