Wasmtime's C/C++ API

API Documentation

The API documentation for the Wasmtime C library is hosted here..

Using in a C/C++ Project

Using a Pre-Built Static or Dynamic Library

Each release on Wasmtime's GitHub Releases page has pre-built binaries for both static and dynamic libraries for a variety of architectures and operating systems attached, as well as header files you can include.

Building Wasmtime's C/C++ API from Source

To use Wasmtime from a C or C++ project, you must have CMake and a Rust toolchain installed.

From the root of the Wasmtime repository, run the following commands:

$ cmake -S crates/c-api -B target/c-api --install-prefix "$(pwd)/artifacts"
$ cmake --build target/c-api
$ cmake --install target/c-api

These commands will produce the following files:

• artifacts/lib/libwasmtime.{a,lib}: Static Wasmtime library. Exact extension depends on your operating system.

• artifacts/lib/libwasmtime.{so,dylib,dll}: Dynamic Wasmtime library. Exact extension depends on your operating system.

• artifacts/include/**.{h,hh}: Header files for working with Wasmtime.

Using in a C++ Project

A header only C++ API is also offered as wasmtime.hh, which is built on top of the C API. Its located next to the C headers when you download a pre-built library, or when building from source. C++17 is required.

Using in a Rust Project

If you have a Rust crate that contains bindings to a C or C++ library that uses Wasmtime, you can link the Wasmtime C API using Cargo.

1. Add a dependency on the wasmtime-c-api-impl crate to your Cargo.toml. Note that package name differs from the library name.

[dependencies]
wasmtime-c-api = { version = "16.0.0", package = "wasmtime-c-api-impl" }

2. In your build.rs file, when compiling your C/C++ source code, add the C wasmtime-c-api headers to the include path:

fn main() {
    let mut cfg = cc::Build::new();

    // Add to the include path the wasmtime headers and the standard
    // Wasm C API headers.
    cfg
        .include(std::env::var("DEP_WASMTIME_C_API_INCLUDE").unwrap());

    // Compile your C code.
    cfg
        .file("src/your_c_code.c")
        .compile("your_library");
}

Testing

Running tests for the C API can be done using cmake from the root of the repo:

$ cmake -S examples -B examples/build -DBUILD_SHARED_LIBS=OFF -DBUILD_TESTS=ON -DCMAKE_BUILD_TYPE=Debug
$ cmake --build examples/build --config Debug
$ CTEST_OUTPUT_ON_FAILURE=1 cmake --build examples/build --config Debug --target test

To build and run a subset of tests by name:

$ cmake --build examples/build --config Debug
$ ctest --test-dir examples/build --output-on-failure -R $MY_TEST

where $MY_TEST is the test name or glob pattern; for example, MemoryType.Simple to run that one particular test or TypedFunc.* to run all typed function tests.

To run under gdb:

$ gdb --args ctest --test-dir examples/build/ --output-on-failure -R $MY_TEST
(gdb) set follow-fork-mode child
(gdb) run

To run under rr:

$ rr record ctest --test-dir examples/build/ --output-on-failure -R $MY_TEST
$ rr replay