What is Dart: ffi (Foreign Function Interface)

Overview

Dart FFI (Foreign Function Interface) allows Dart code to directly call functions written in C (or other languages compiled to native shared libraries). It bridges Dart and native code without a platform channel.

When to Use Dart FFI

Basic FFI Example

dartCopy
// lib/native_math.dart
import 'dart:ffi';
import 'dart:io';

// Load the shared library
final DynamicLibrary nativeLib = Platform.isAndroid
    ? DynamicLibrary.open('libnative.so')
    : DynamicLibrary.process(); // iOS links statically

// C function signature: int add(int a, int b);
typedef AddC = Int32 Function(Int32 a, Int32 b);
typedef AddDart = int Function(int a, int b);

// Look up the function
final add = nativeLib.lookupFunction<AddC, AddDart>('add');

void main() {
  print(add(3, 4)); // Calls native C: 7
}

C Code Side (native_math.c)

cCopy
// native_math.c
#include <stdint.h>

int32_t add(int32_t a, int32_t b) {
    return a + b;
}

// More complex example
double calculate_average(double* arr, int32_t length) {
    double sum = 0;
    for (int i = 0; i < length; i++) sum += arr[i];
    return sum / length;
}

FFI Types Mapping

Int8

int8_t

int

Int32

int32_t

int

Int64

int64_t

int

Float

float

double

Double

double

double

Bool

bool

bool

Pointer<T>

T*

Pointer<T>

Void

void

void

With Strings and Structs

dartCopy
import 'dart:ffi';
import 'package:ffi/ffi.dart'; // For Utf8 support

// Calling C function that takes/returns strings
typedef GetMessageC = Pointer<Utf8> Function();
final getMessage = nativeLib
    .lookupFunction<GetMessageC, Pointer<Utf8> Function()>('get_message');

final messagePtr = getMessage();
print(messagePtr.toDartString()); // Convert C string to Dart String

FFI vs Platform Channels

Note: FFI is powerful but complex. For most Flutter plugins, Method Channels are simpler. Use FFI when you need direct C library access with minimal overhead.