Interact with native memory using dart:ffi

The dart:ffi (Foreign Function Interface) library is a core Dart SDK library that provides the low-level APIs to call C-ABI functions from Dart.

Rather than code generation tools like Pigeon, FFIgen, or JNIgen, dart:ffi is the underlying technology that powers these tools and enables native memory interop.

Dart memory is automatically garbage collected while native C memory is manually managed, so use dart:ffi and package:ffi to bridge this gap.

The two most common scenarios when package:ffi is needed alongside dart:ffi are memory allocation and C string conversion.

With memory allocation, use package:ffi to allocate space on the system heap for native arguments, and manually free that memory when done to prevent memory leaks.

With data conversion, use package:ffi to convert Dart strings into C strings (Pointer<Utf8> or Pointer<Utf16>) so they can be read by native C code.

To write C interop code, use two libraries:

• dart:ffi: Built into the core Dart SDK and required for doing FFI interop. It provides native representation types, pointers, structs, and function lookup signatures.
• package:ffi: A companion package that contains utilities helpful in common C interop use cases, such as memory allocation (calloc and malloc) and C string conversion helpers.

FFI calls are synchronous and run on the thread on which they're called. If you invoke a heavy or blocking C function on your Flutter app's main UI thread, your app may freeze or drop frames. To prevent this, execute blocking FFI calls inside a background Dart isolate using Isolate.run.

To explore examples of memory allocation, string conversion, and dynamic library loading, refer to these Dart interop resources:

• C interop guide (includes code examples for pointers, memory allocation, and structs)
• dart:ffi API reference
• package:ffi on pub.dev