This documentation is an overview and API reference for the C API of Wasmtime. The C API is spread between three different header files:

The wasmtime.h header file includes all the other header files and is the main header file you'll likely be using. The wasm.h header file comes directly from the WebAssembly/wasm-c-api repository, and at this time the upstream header file does not have documentation so Wasmtime provides documentation here. It should be noted some semantics may be Wasmtime-specific and may not be portable to other engines.

Installing the C API

To install the C API from precompiled binaries you can download the appropriate binary from the releases page of Wasmtime. Artifacts for the C API all end in "-c-api" for the filename.

Each archive contains an include directory with necessary headers, as well as a lib directory with both a static archive and a dynamic library of Wasmtime. You can link to either of them as you see fit.

Installing the C API through CMake

CMake can be used to make the process of linking and compiling easier. An example of this if you have wasmtime as a git submodule at third_party/wasmtime:

add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/third_party/wasmtime/crates/c-api
${CMAKE_CURRENT_BINARY_DIR}/wasmtime)
...
target_include_directories(YourProject PUBLIC wasmtime)
target_link_libraries(YourProject PUBLIC wasmtime)

BUILD_SHARED_LIBS is provided as a define if you would like to build a shared library instead. You must distribute the appropriate shared library for your platform if you do this.

Linking against the C API

You'll want to arrange the include directory of the C API to be in your compiler's header path (e.g. the -I flag). If you're compiling for Windows and you're using the static library then you'll also need to pass -DWASM_API_EXTERN= and -DWASI_API_EXTERN= to disable dllimport.

Your final artifact can then be linked with -lwasmtime. If you're linking against the static library you may need to pass other system libraries depending on your platform:

Linux - -lpthread -ldl -lm
macOS - no extra flags needed
Windows - ws2_32.lib advapi32.lib userenv.lib ntdll.lib shell32.lib ole32.lib bcrypt.lib

Building from Source

The C API is located in the crates/c-api directory of the Wasmtime repository. To build from source you'll need a Rust compiler and a checkout of the wasmtime project. Afterwards you can execute:

$ cargo build --release -p wasmtime-c-api

This will place the final artifacts in target/release, with names depending on what platform you're compiling for.

Other resources

Some other handy resources you might find useful when exploring the C API documentation are:

Rust wasmtime crate documentation - although this documentation is for Rust and not C, you'll find that many functions mirror one another and there may be extra documentation in Rust you find helpful. If you find yourself having to frequently do this, though, please feel free to file an issue.
C embedding examples are available online and are tested from the Wasmtime repository itself.
Contribution documentation for Wasmtime in case you're interested in helping out!