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. This is 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, and your progress syncs across the web and the CoddyKit app. The Kotlin Multiplatform Academy course includes 4 lessons in total.
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. 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. The Kotlin Multiplatform Academy course includes 4 lessons in total.
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, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.
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