cinterop with C Libraries
Bind a C dependency for use in shared code.
cinterop with C Libraries is a free Kotlin Multiplatform Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Kotlin Multiplatform Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Reaching Into C
Sometimes the code you need is a plain C library. Kotlin/Native can call it directly through a tool called cinterop. 🔌
What cinterop Produces
cinterop reads C headers and generates Kotlin bindings. After that, the C functions and types look like ordinary Kotlin declarations you can call.
The .def File
You describe the library in a small def file: which headers to read and which library to link. This is the recipe cinterop follows.
headers = mylib.h
package = mylibWire It Into Gradle
Inside the kotlin block you register a cinterop entry for your target. Gradle then runs the tool and adds the generated bindings to compilation.
cinterops.create("mylib")Calling a C Function
Once generated, a C function is just a Kotlin function. Import it from your def package and call it like any other shared function.
import mylib.compute
val r = compute(21)C Pointers Become CPointer
A raw C pointer maps to Kotlin CPointer. It is typed, so the compiler knows what it points at instead of leaving you with a bare address.
Memory You Must Manage
C does not free things for you. Allocate inside a memScoped block so Kotlin releases the native memory automatically when the block ends.
memScoped {
val buf = allocArray<ByteVar>(16)
}Strings Cross the Line
Use helpers to convert between Kotlin and C strings. A Kotlin String becomes a C buffer with cstr, and you convert back when reading results.
Opaque Types and Structs
C structs map to Kotlin classes with field access. An opaque type you never inspect is just a pointer you pass straight back to the library.
Keep It on Native Targets
cinterop bindings exist only for Kotlin/Native targets like iOS. Wrap the calls behind expect/actual so commonMain stays platform-free.
Wrap, Then Expose
Hide pointers and memScoped behind a friendly Kotlin API. Callers get clean types and never touch raw C details directly.
Quick Check
A quick check on managing C memory from Kotlin.
Recap: cinterop
You saw that a def file plus Gradle generates Kotlin bindings for a C library, pointers map to CPointer, and memScoped manages native memory. 🎉
Frequently asked questions
Is the “cinterop with C Libraries” lesson free?
Yes — the full text of “cinterop with C Libraries” is free to read here on the web, and the Kotlin Multiplatform Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Kotlin Multiplatform Academy course, upgrade to CoddyKit PRO.
What will I learn in “cinterop with C Libraries”?
Bind a C dependency for use in shared code. You practise Kotlin Multiplatform Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Kotlin Multiplatform Academy?
No prior experience is required. Kotlin Multiplatform Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “cinterop with C Libraries” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Kotlin Multiplatform Academy lesson?
Yes. Every Kotlin Multiplatform Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Use Apple Frameworks from Kotlin
- Memory & ARC in Kotlin/Native
- cinterop with C Libraries
- Wrap a Native SDK Cleanly