As docs refers

There is an old and new way of typedef

in general: the new way is a bit clearer and more readable.

in details:

typedef G = List<int> Function(int); // New form.
typedef List<int> H(int i); // Old form.

Note that the name of the parameter is required in the old form, but the type may be omitted. In contrast, the type is required in the new form, but the name may be omitted.

As well as

The reason for having two ways to express the same thing is that the new form seamlessly covers non-generic functions as well as generic ones, and developers might prefer to use the new form everywhere, for improved readability.

So the applied changes were, to adopt to this new way of writing typedef, as well as, minor changes for code re-structuring were applied, where four functions were created to work as standalone unit of code

Error: Expected 0 type arguments.
class Utf8 extends Struct<Utf8> {
                   ^
Error: Expected 0 type arguments.
class Utf16 extends Struct<Utf16> {
                    ^
Error: Type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart'.
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  static int strlen(Pointer<Utf8> string) {
                                  ^
Error: Type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart'.
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  static String fromUtf8(Pointer<Utf8> string) {
                                       ^
Error: Type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer' in the return type.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  static Pointer<Utf8> toUtf8(String string) {
                             ^
 Error: Type argument 'Utf16' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer' in the return type.
 - 'Utf16' is from 'package:ffi/src/utf16.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  static Pointer<Utf16> toUtf16(String s) {
                               ^
Error: Type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  final systemP = dylib.lookupFunction<SystemC, SystemDart>('system');
                        ^
Error: Inferred type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart'.
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final systemP = dylib.lookupFunction<SystemC, SystemDart>('system');
        ^
Error: Inferred type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final cmdP = Utf8.toUtf8(command);
        ^
Error: Type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try changing type arguments so that they conform to the bounds.
  final systemP = dylib.lookupFunction<SystemC, SystemDart>('system');
                        ^
Error: Inferred type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final systemP = dylib.lookupFunction<SystemC, SystemDart>('system');
        ^
Error: Inferred type argument 'Utf8' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final cmdP = Utf8.toUtf8(command);
        ^
Error: Inferred type argument 'Utf16' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf16' is from 'package:ffi/src/utf16.dart' .
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final operationP = Utf16.toUtf16(operation);
        ^
Error: Inferred type argument 'Utf16' doesn't conform to the bound 'NativeType' of the type variable 'T' on 'Pointer'.
 - 'Utf16' is from 'package:ffi/src/utf16.dart'.
 - 'NativeType' is from 'dart:ffi'.
Try specifying type arguments explicitly so that they conform to the bounds.
  final fileP = Utf16.toUtf16(file);
        ^
Error: The argument type 'Pointer<Utf16>' can't be assigned to the parameter type 'Pointer<NativeType>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Utf16' is from 'package:ffi/src/utf16.dart' .
 - 'NativeType' is from 'dart:ffi'.
      ffi.nullptr, operationP, fileP, ffi.nullptr, ffi.nullptr, SW_SHOWNORMAL);
                   ^
Error: The argument type 'Pointer<Utf16>' can't be assigned to the parameter type 'Pointer<NativeType>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Utf16' is from 'package:ffi/src/utf16.dart'.
 - 'NativeType' is from 'dart:ffi'.
      ffi.nullptr, operationP, fileP, ffi.nullptr, ffi.nullptr, SW_SHOWNORMAL);
                               ^
Error: The method 'asExternalTypedData' isn't defined for the class 'Pointer<Uint8>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Uint8' is from 'dart:ffi'.
Try correcting the name to the name of an existing method, or defining a method named 'asExternalTypedData'.
    final Uint8List nativeString = array.asExternalTypedData(count: _maxSize);
                                         ^^^^^^^^^^^^^^^^^^^
Error: The method 'asExternalTypedData' isn't defined for the class 'Pointer<Uint8>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Uint8' is from 'dart:ffi'.
Try correcting the name to the name of an existing method, or defining a method named 'asExternalTypedData'.
        string.cast<Uint8>().asExternalTypedData(count: length).buffer,
                             ^^^^^^^^^^^^^^^^^^^
Error: Method not found: 'Pointer.allocate'.
        Pointer<Uint8>.allocate(count: units.length + 1);
                       ^^^^^^^^
Error: The method 'asExternalTypedData' isn't defined for the class 'Pointer<Uint8>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Uint8' is from 'dart:ffi'.
Try correcting the name to the name of an existing method, or defining a method named 'asExternalTypedData'.
        result.asExternalTypedData(count: units.length + 1);
               ^^^^^^^^^^^^^^^^^^^
Error: The getter 'addressOf' isn't defined for the class 'Utf8'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' .
Try correcting the name to the name of an existing getter, or defining a getter or field named 'addressOf'.
  String toString() => fromUtf8(addressOf);
                                ^^^^^^^^^
Error: Method not found: 'Pointer.allocate'.
        Pointer<Uint16>.allocate(count: units.length + 1);
                        ^^^^^^^^
Error: The method 'asExternalTypedData' isn't defined for the class 'Pointer<Uint16>'.
 - 'Pointer' is from 'dart:ffi'.
 - 'Uint16' is from 'dart:ffi'.
Try correcting the name to the name of an existing method, or defining a method named 'asExternalTypedData'.
        result.asExternalTypedData(count: units.length + 1);
               ^^^^^^^^^^^^^^^^^^^
Exception: Errors during snapshot creation: null
#0      KernelSnapshot.build (package:flutter_tools/src/build_system/targets/dart.dart:230:7)
<asynchronous suspension>
#1      _BuildInstance._invokeInternal (package:flutter_tools/src/build_system/build_system.dart:526:25)
<asynchronous suspension>
#2      _BuildInstance.invokeTarget.<anonymous closure> (package:flutter_tools/src/build_system/build_system.dart:481:35)
#3      new Future.sync (dart:async/future.dart:222:31)
#4      AsyncMemoizer.runOnce (package:async/src/async_memoizer.dart:43:45)
#5      _BuildInstance.invokeTarget (package:flutter_tools/src/build_system/build_system.dart:481:21)
<asynchronous suspension>
<asynchronous suspension>
#6      BuildSystem.build (package:flutter_tools/src/build_system/build_system.dart:419:36)
#7      _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:43:6)
#8      BuildSystem.build (package:flutter_tools/src/build_system/build_system.dart:400:28)
#9      buildWithAssemble (package:flutter_tools/src/bundle.dart:125:48)
#10     _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:43:6)
#11     buildWithAssemble (package:flutter_tools/src/bundle.dart:99:31)
#12     BundleBuilder.build (package:flutter_tools/src/bundle.dart:75:11)
#13     _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:43:6)
#14     BundleBuilder.build (package:flutter_tools/src/bundle.dart:52:21)
#15     BuildBundleCommand.runCommand (package:flutter_tools/src/commands/build_bundle.dart:126:25)
#16     _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:43:6)
#17     BuildBundleCommand.runCommand (package:flutter_tools/src/commands/build_bundle.dart:97:42)
#18     FlutterCommand.verifyThenRunCommand (package:flutter_tools/src/runner/flutter_command.dart:557:18)
#19     _asyncThenWrapperHelper.<anonymous closure> (dart:async-patch/async_patch.dart:71:64)
#20     _rootRunUnary (dart:async/zone.dart:1132:38)
#21     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
#22     _FutureListener.handleValue (dart:async/future_impl.dart:137:18)
#23     Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:678:45)
#24     Future._propagateToListeners (dart:async/future_impl.dart:707:32)
#25     Future._completeWithValue (dart:async/future_impl.dart:522:5)
#26     Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:552:7)
#27     _rootRun (dart:async/zone.dart:1124:13)
#28     _CustomZone.run (dart:async/zone.dart:1021:19)
#29     _CustomZone.runGuarded (dart:async/zone.dart:923:7)
#30     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:963:23)
#31     _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
#32     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)
#33     _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:116:13)
#34     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:173:5)

flutter doctor

[✓] Flutter (Channel master, v1.10.15-pre.307, on Mac OS X 10.15.1 19B88)
 
[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
[!] Xcode - develop for iOS and macOS (Xcode 11.1)
    ✗ CocoaPods installed but not working.
        You appear to have CocoaPods installed but it is not working.
        This can happen if the version of Ruby that CocoaPods was installed with is different from the one being used to invoke it.
        This can usually be fixed by re-installing CocoaPods. For more info, see https://github.com/flutter/flutter/issues/14293.
      To re-install CocoaPods, run:
        sudo gem install cocoapods
[✓] Chrome - develop for the web
[!] Android Studio (version 3.5)
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
[✓] IntelliJ IDEA Community Edition (version 2019.2.3)
[✓] VS Code (version 1.39.2)
[✓] Connected device (3 available)

! Doctor found issues in 2 categories.

Created per @kevmoo's request in https://github.com/dart-lang/samples/pull/81#issuecomment-756531146

Hey @RedBrogdon and @johnpryan,

I started porting the travis test set to Github Actions and I hit something of a head scratcher. I realised that our Travis tests purport to run tests on windows... using a shell script runner. Which makes almost no sense. Unless the Travis windows machines have cygwin or similar installed.

Note, the windows tests appear to pass, even though some of the tests are specifically written for linux only (and test for the presence of a generated .so file ... as opposed to the .dll or .dylib that should be created on Windows and macOS respectively.

When attempting to run the unmodified sample at https://github.com/dart-lang/samples/blob/master/ffi/system-command/macos.dart I get the following error:

➜  dart_ffi: $ dart macos.dart
Crash when compiling file:///Users/thinkdigital/github/dart_ffi/macos.dart,
at character offset 62893:
macos.dart:854:240: Internal problem: Unhandled ParserRecovery in handleType.
        <td id="LC21" class="blob-code blob-code-inner js-file-line"><span class="pl-k">typedef</span> <span class="pl-c1">SystemC</span> <span class="pl-k">=</span> ffi.<span class="pl-c1">Int32</span> <span class="pl-c1">Function</span>(ffi.<span class="pl-c1">Pointer</span><span class="pl-k">&lt;</span><span class="pl-c1">Utf8</span><span class="pl-k">&gt;</span> command);</td>
                                                                                                                                                                                                                                               ^
#0      internalProblem (package:front_end/src/fasta/problems.dart:45:3)
#1      unhandled (package:front_end/src/fasta/problems.dart:58:10)
#2      BodyBuilder.handleType (package:front_end/src/fasta/kernel/body_builder.dart:2800:7)
#3      ComplexTypeInfo.parseType (package:front_end/src/fasta/parser/type_info_impl.dart:504:25)
#4      Parser.parseFormalParameter (package:front_end/src/fasta/parser/parser.dart:1478:24)
#5      Parser.parseFormalParametersRest (package:front_end/src/fasta/parser/parser.dart:1252:15)
#6      Parser.parseFormalParameters (package:front_end/src/fasta/parser/parser.dart:1216:12)
#7      Parser.parseFormalParametersOpt (package:front_end/src/fasta/parser/parser.dart:1176:15)
#8      DietListener.buildFunctionBody (package:front_end/src/fasta/source/diet_listener.dart:885:22)

using Dart version 2.6:

> [✓] Flutter (Channel master, v1.10.3-pre.65, on Mac OS X 10.14.6 18G95, locale en-US)
>     • Flutter version 1.10.3-pre.65 at /Users/thinkdigital/development/flutter
>     • Framework revision 0df1594ba2 (28 minutes ago), 2019-09-16 15:27:05 -0700
>     • Engine revision 63873d9f42
>     • Dart version 2.6.0 (build 2.6.0-dev.0.0 7799f424f4)

And how to create function pointer?

typedef Pointer GlfwSetKeyCallback(Pointer<GLFWWindow> window, Pointer callback);
glfwSetKeyCallback(_window, dartFunction);```

This is an example of passing a callback method from Dart to C and having that callback method called synchronously. The program is deliberately simple, to not obfuscate exactly what is required to do this one simple thing.

This is our first PR. We're quite willing to accept any fix requests should the code not be as needed.

Updated all the Makefiles to run dart:ffi examples on a Windows machine.

Use make dll on windows.

Which currently creates hello_world.dylib (minimal code changes) instead of hello_world.dll which should be the standard name.

Also, removed annotations in structs/structs.dart

There is one place I expect static analysis to pick it up, but instead it's a runtime error. It's in the switch case in https://github.com/dart-lang/samples/pull/69/commits/4859de40719de60f32c4153095ebdfc5e677b22c#diff-9e0b069eeab563d6a82928ebc03a01c5R39 , compiled with Dart VM version: 2.9.0-14.1.beta (beta) (Tue Jun 9 10:52:57 2020 +0200) on "macos_x64"

Problem

On macOS, running the primitive sample code after proper CMaking the C lib gives the following error

$ !dart
dart primitives.dart
Unhandled exception:
Invalid argument(s): Failed to load dynamic library (dlopen(./primitives_library/libprimtives.dylib, 1): image not found)
#0      _open (dart:ffi-patch/ffi_dynamic_library_patch.dart:10:55)
#1      new DynamicLibrary.open (dart:ffi-patch/ffi_dynamic_library_patch.dart:19:12)
#2      main (file:///Users/kakyo/Desktop/_task/MMT/research/hello-mamguest/hello_dart/primitives/primitives.dart:41:32)
#3      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:305:19)
#4      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:172:12)

Fix

$ sdiff -l theirs/ffi/primitives/primitives.dart mine/primitives/primitives.dart | cat -n | grep -v -e '($'
5	import 'dart:ffi';					      |	import 'dart:ffi' as ffi;
41	  final dylib = DynamicLibrary.open(path);		      |	  final dylib = ffi.DynamicLibrary.open(path);

I have this code I can't get it to work, no errors are shown

import 'dart:ffi';

import 'package:ffi/ffi.dart';

class HWND extends Struct {}

typedef GetActiveWindowC = Pointer<HWND> Function();

typedef GetActiveWindowDart = Pointer<HWND> Function();

typedef GetWindowTextC = Int32 Function(Pointer<HWND> hWnd, Pointer<Utf8> lpString, Int32 nMaxCount);

typedef GetWindowTextDart = int Function(Pointer<HWND> hWnd, Pointer<Utf8> lpString, int nMaxCount);

void main() {
  var path = r'User32.dll';
  final dylib = DynamicLibrary.open(path);

  final GetActiveWindowPointer =
      dylib.lookup<NativeFunction<GetActiveWindowC>>('GetActiveWindow');
  final GetActiveWindowDart GetActiveWindow =
      GetActiveWindowPointer.asFunction<GetActiveWindowDart>();

  final GetWindowTextPointer =
      dylib.lookup<NativeFunction<GetWindowTextC>>('GetWindowTextA');
  final GetWindowTextDart GetWindowText =
      GetWindowTextPointer.asFunction<GetWindowTextDart>();

  final Pointer<HWND> hWnd = GetActiveWindow();

  final Pointer<Utf8> lpString = allocate();

  final int nMaxCount = 256;

  final result = GetWindowText(hWnd, lpString, nMaxCount);

  final text = Utf8.fromUtf8(lpString);

  print(result);
  print(text);
}

current output:

0

Dart VM version: 2.6.0-dev.0.0 (Tue Sep 10 12:55:30 2019 +0200) on "linux_x64" Ubuntu 16.04

The documentation at

https://dart.dev/guides/libraries/c-interop

is, as it claims to be, MacOS-specific. Building hello_world on Linux involves changing the Makefile. Here's one that works:

hello: hello.c hello.h 
        gcc -o a.out hello.c 
 
dylib: hello.c hello.h 
        gcc -c -fPIC hello.c -o hello.o 
        gcc -shared hello.o -o ../hello_world.dylib 

Just thought it ought to be added.

Bumps actions/cache from 3.0.11 to 3.2.2.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

Bumps actions/checkout from 3.1.0 to 3.2.0.

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

Please ignore my ignorance but while I'm trying to learn more about ffi I studied the structs sample.

I just don't understand how freeing myHomeUtf8 does not leave a dangling pointer in the the native Place struct.

https://github.com/dart-lang/samples/blob/master/ffi/structs/structs_library/structs.c#L58

  struct Place create_place(char *name, double latitude, double longitude)
  {
    struct Place place;
    place.name = name;
    // ...

https://github.com/dart-lang/samples/blob/master/ffi/structs/structs.dart#L94

  final myHomeUtf8 = 'My Home'.toNativeUtf8();
  final createPlace =
      dylib.lookupFunction<CreatePlaceNative, CreatePlace>('create_place');
  final place = createPlace(myHomeUtf8, 42.0, 24.0);
  calloc.free(myHomeUtf8);
  final name = place.name.toDartString();

I understand that someone needs to free that memory and that in a sample memory management might not be the biggest concern. But accessing the name after freeing the memory seems especially odd to me.

Most likely I'm just missing something here.

We should consider adding a sample with finalizers.

More info in the first post in https://github.com/dart-lang/sdk/issues/35770.

There are a ton of questions around using the C API for finalizers, so having a sample would be a good thing.

We might want to add a sample for asynchronous callbacks to this repo. This requires compiling against dart_api(_dl).h.

See the samples in the SDK repo:

• Dart code: https://github.com/dart-lang/sdk/tree/master/samples/ffi/async
• C code: https://github.com/dart-lang/sdk/blob/master/runtime/bin/ffi_test/ffi_test_functions_vmspecific.cc

Context: https://github.com/dart-lang/sdk/issues/46135

Hi, I try to run the example as is and after running cmake command running the command make and getting error: make: *** No targets specified and no makefile found