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.

Exercise 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());.

Show example solution

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());
}

Test yourself

Library loading

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

Show answer

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

What is the file extension of a C library on Linux?
- .dll
- .dylib
- .so
- .exe
Show answer

.so — on Linux, C libraries use the .so extension.
Match the DynamicLibrary methods

DynamicLibrary.open

Load from file
DynamicLibrary.process

Load from process
DynamicLibrary.executable

From executable
lookupFunction

Symbol lookup

Next lesson: Native function

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