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DynamicLibrary

Learn native loading with DynamicLibrary.

DynamicLibrary

DynamicLibrary is the dart:ffi class that represents C libraries on the Dart side. A library is loaded from a file with DynamicLibrary.open('libmylib.so'), from the process with DynamicLibrary.process(), or from the executable with DynamicLibrary.executable().

The opened library is a handle; symbols (functions) are looked up via lookupFunction. If the library cannot be loaded, an ArgumentError is thrown. The file extension depends on the platform: Linux .so, macOS .dylib, Windows .dll.

Symbol lookup

Once a DynamicLibrary is loaded, its functions are looked up with lookupFunction. Each function is represented by a symbol name; for example, add may be int add(int, int) on the C side.

If a symbol is not found, an ArgumentError is thrown. FFI maps between native and Dart types: Int32 ↔ int, Double ↔ double, Pointer<Void> ↔ Pointer<NativeType>. The mapping is declared statically.

Practice A LibraryLoader class

Define a LibraryLoader class with final String path; final String platform; LibraryLoader(this.path, this.platform); field and constructor. Add a String describe() => 'loading $path on $platform'; method. In main create final l = LibraryLoader('libmylib.so', 'Linux');; print with print(l.describe());.

Starter code

main.dart
void main() {
  // define a LibraryLoader class (path, platform; describe)
  // create a LibraryLoader; print describe()
}

Sample solution

main.dart
class LibraryLoader {
  final String path;
  final String platform;
  LibraryLoader(this.path, this.platform);
  String describe() => 'loading $path on $platform';
}

void main() {
  final l = LibraryLoader('libmylib.so', 'Linux');
  print(l.describe());
}

Expected output

loading libmylib.so on Linux

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Library loading

Question 
final lib = DynamicLibrary.____('libmylib.so');
Answer 
final lib = DynamicLibrary.open('libmylib.so');

Explanation: DynamicLibrary.open loads a C library from a file.

2 What is the file extension of a C library on Linux?

  • .dll
  • .dylib
  • .so Correct answer
  • .exe

Explanation: on Linux, C libraries use the .so extension.

3 Match the DynamicLibrary methods

Term Meaning
DynamicLibrary.open Load from file
DynamicLibrary.process Load from process
DynamicLibrary.executable From executable
lookupFunction Symbol lookup

All lessons in Expert

1 Language design

  1. Dart design
  2. Sound null safety
  3. Type system
  4. Subtyping
  5. Records and patterns
  6. Summary - Language design

2 Compiler internals

  1. Compilation pipeline
  2. AST
  3. Kernel
  4. Code generation
  5. dartaotruntime
  6. Summary - Compiler internals

3 FFI

  1. dart:ffi
  2. DynamicLibrary
  3. Native function
  4. Struct
  5. Pointer
  6. Summary - FFI

4 Native extension

  1. What are extensions?
  2. Extension method
  3. Extension operator
  4. Generic extension
  5. Extension vs subclass
  6. Summary - Native extension

5 Build system

  1. build_runner
  2. Builder
  3. source_gen
  4. Analyzer
  5. Custom lint
  6. Summary - Build system

6 Architecture

  1. Clean architecture
  2. Feature-based
  3. Repository
  4. Dependency injection
  5. SOLID
  6. Summary - Architecture

7 Advanced testing

  1. Integration tests
  2. Property tests
  3. Advanced mocking
  4. Coverage
  5. Golden tests
  6. Summary - Advanced testing

8 Expert final

  1. Project design
  2. FFI
  3. Codegen
  4. Architecture
  5. Putting it together