C interop using dart:ffi

As of Dart 2.7, dart:ffi is in beta, and breaking API changes might still happen. If you’re developing a Flutter app, you can get access to dart:ffi by using the Flutter dev channel, as described in the

API documentation is available from the dev channel: dart:ffi API reference.

The following examples show how to use the dart:ffi library:

The has the minimum necessary code for calling a C library.

The hello_world example has the following files:

Source file	Description
hello.dart	A Dart file that uses the function from a C library.
	The usual Dart pubspec, with a lower bounds on the SDK that’s at least 2.5.
	Declares the `hello_world()` function.
hello_library/hello.c	A C file that imports `hello.h` and defines the `hello_world()` function.
	A CMake build file for compiling the C code into a dynamic library.

Here’s an example of building the dynamic library and executing the Dart app:

On macOS, the Dart VM () can load only signed libraries. For details and workarounds, see SDK issue #38314.

The illustrates the steps for using dart:ffi to call a C function:

Import dart:ffi.
Create a typedef for the variable that you’ll use when calling the C function.
Open the dynamic library that contains the C function.
Get a reference to the C function, and put it into a variable.
Call the C function.

Here’s the code for each step.

Import dart:ffi.
```
import 'dart:ffi' as ffi;
```
Open the dynamic library that contains the C function.
Get a reference to the C function, and put it into a variable. This code uses the typedefs defined in steps 2 and 3, along with the dynamic library variable from step 4.
```
  final HelloWorld hello = dylib
   .lookup<ffi.NativeFunction<hello_world_func>>('hello_world')
   .asFunction();
```
Call the C function.

Once you understand the hello_world example, you should be ready to look at the other dart:ffi examples.