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Wasmer Runtime C API

Wasmer is a standalone WebAssembly runtime for running WebAssembly outside of the browser, supporting WASI and Emscripten.

The Wasmer Runtime C API exposes a C and a C++ API to interact with the Wasmer Runtime, so you can use WebAssembly anywhere.


Since the Wasmer runtime is written in Rust, the C and C++ API are designed to work hand-in-hand with its shared library. The C and C++ header files, namely wasmer.h and wasmer.hh are documented in the docs.

Their source code can be found in the source tree of the wasmer-runtime-c-api crate. The C and C++ header files along with the runtime shared libraries (.so, .dylib, .dll) can also be downloaded in the Wasmer release page.

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;


You can check more examples of how to use the Wasmer C API here:



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