'C interop using dart:ffi' page mention package:ffi

[dcharkes]

We should get package:ffi mentioned (utf conversions, memory management) on https://dart.dev/guides/libraries/c-interop.

cc @mit-mit

[mit-mit]

+1

[kwalrath]

There are a couple of different approaches we could take, depending on how much we want to emphasize package:ffi:

1. Add package:ffi (and maybe package:ffigen?) to the first paragraph, and link to its docs from the second paragraph. Maybe add (or link to) examples of using it.

2. Treat it like we do package:ffigen, where's it's covered only in a separate section.

We should also add package:ffi to https://dart.dev/guides/libraries/useful-libraries#packages-that-correspond-to-sdk-libraries, and dart:ffi to https://dart.dev/guides/libraries.

[mit-mit]

In practice, I'd think that anyone writing FFI code will be using the package. So I'd just add some example of using it for utf conversions and freeing memory.

[kwalrath]

Where's some good sample code we can use?

[dcharkes]

The samples repo contains code, but misses some memory management.

https://github.com/dart-lang/samples/blob/master/ffi/structs/structs.dart#L65-L69

Here's a version of reverse with memory management:

void main(List<String> arguments) {
  final dylib = DynamicLibrary.open('some/path/to/a/dynamic/library');

  final hello = 'Hello'.toNativeUtf8();
  final reverse = dylib.lookupFunction<Void Function(Pointer<Utf8>),
      void Function(Pointer<Utf8>)>('reverse');
  reverse(hello);
  print(hello.toDartString());
  malloc.free(hello);
}

[atsansone]

@dcharkes : I'm having difficulty finding information on package:ffi that's not dart:ffi. Did something change between when this issue was filed and now? Should I close this?

[dcharkes]

I'm having difficulty finding information on package:ffi that's not dart:ffi.

The API documentation for package:ffi is here: https://pub.dev/documentation/ffi/latest/ffi/ffi-library.html

Did something change between when this issue was filed and now? Should I close this?

No and no, package:ffi is not yet mentioned on https://dart.dev/guides/libraries/c-interop.