wasmer-c-api 1.0.0-alpha5

Wasmer C API library
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wasmer-c-api Build Status Join Wasmer Slack MIT License

This crate exposes a C and a C++ API for the Wasmer runtime. It also fully supports the wasm-c-api common API.


Once you install Wasmer in your system, the shared object files and the headers will be automatically available inside the Wasmer installed path.

The C (wasmer.h) and C++ (wasmer.hh) header files can be found in the Wasmer include directory:

wasmer config --includedir

The runtime shared libraries (.so, .dylib, .dll) can be found in the Wasmer lib directory:

wasmer config --libdir

Note: You can also download the libraries or header files directly from Wasmer release page.

The full C API documentation can be found here: https://wasmerio.github.io/wasmer/c-api/

Here is a simple example to use the C API:

#include <stdio.h>
#include "../wasmer.h"
#include <assert.h>
#include <stdint.h>
int main()
    // Read the Wasm file bytes.
    FILE *file = fopen("sum.wasm", "r");
    fseek(file, 0, SEEK_END);
    long len = ftell(file);
    uint8_t *bytes = malloc(len);
    fseek(file, 0, SEEK_SET);
    fread(bytes, 1, len, file);
    // Prepare the imports.
    wasmer_import_t imports[] = {};
    // Instantiate!
    wasmer_instance_t *instance = NULL;
    wasmer_result_t instantiation_result = wasmer_instantiate(&instance, bytes, len, imports, 0);
    assert(instantiation_result == WASMER_OK);
    // Let's call a function.
    // Start by preparing the arguments.
    // Value of argument #1 is `7i32`.
    wasmer_value_t argument_one;
    argument_one.tag = WASM_I32;
    argument_one.value.I32 = 7;
    // Value of argument #2 is `8i32`.
    wasmer_value_t argument_two;
    argument_two.tag = WASM_I32;
    argument_two.value.I32 = 8;
    // Prepare the arguments.
    wasmer_value_t arguments[] = {argument_one, argument_two};
    // Prepare the return value.
    wasmer_value_t result_one;
    wasmer_value_t results[] = {result_one};
    // Call the `sum` function with the prepared arguments and the return value.
    wasmer_result_t call_result = wasmer_instance_call(instance, "sum", arguments, 2, results, 1);
    // Let's display the result.
    printf("Call result:  %d\n", call_result);
    printf("Result: %d\n", results[0].value.I32);
    // `sum(7, 8) == 15`.
    assert(results[0].value.I32 == 15);
    assert(call_result == WASMER_OK);
    return 0;


Tests are run using the release build of the library. If you make changes or compile with non-default features, please ensure you rebuild in release mode for the tests to see the changes.

The tests can be run via cargo test, such as:

$ cargo test --release -- --nocapture

To run tests manually, enter the lib/c-api/tests directory and run the following commands:

$ cmake .
$ make
$ make test


The Wasmer binary ships with an utility tool that outputs config in the pkg-config format.

You can use it like:

wasmer config --pkg-config > $PKG_CONFIG_PATH/wasmer.pc


Wasmer is primarily distributed under the terms of the MIT license (LICENSE).