1 #include <fstream> 2 #include <iostream> 3 #include <sstream> 4 #include <wasmtime.hh> 5 6 using namespace wasmtime; 7 8 std::string readFile(const char *name) { 9 std::ifstream watFile; 10 watFile.open(name); 11 std::stringstream strStream; 12 strStream << watFile.rdbuf(); 13 return strStream.str(); 14 } 15 16 int main() { 17 // First the wasm module needs to be compiled. This is done with a global 18 // "compilation environment" within an `Engine`. Note that engines can be 19 // further configured through `Config` if desired instead of using the 20 // default like this is here. 21 std::cout << "Compiling module\n"; 22 Engine engine; 23 auto module = 24 Module::compile(engine, readFile("examples/hello.wat")).unwrap(); 25 26 // After a module is compiled we create a `Store` which will contain 27 // instantiated modules and other items like host functions. A Store 28 // contains an arbitrary piece of host information, and we use `MyState` 29 // here. 30 std::cout << "Initializing...\n"; 31 Store store(engine); 32 33 // Our wasm module we'll be instantiating requires one imported function. 34 // the function takes no parameters and returns no results. We create a host 35 // implementation of that function here. 36 std::cout << "Creating callback...\n"; 37 Func host_func = 38 Func::wrap(store, []() { std::cout << "Calling back...\n"; }); 39 40 // Once we've got that all set up we can then move to the instantiation 41 // phase, pairing together a compiled module as well as a set of imports. 42 // Note that this is where the wasm `start` function, if any, would run. 43 std::cout << "Instantiating module...\n"; 44 auto instance = Instance::create(store, module, {host_func}).unwrap(); 45 46 // Next we poke around a bit to extract the `run` function from the module. 47 std::cout << "Extracting export...\n"; 48 auto run = std::get<Func>(*instance.get(store, "run")); 49 50 // And last but not least we can call it! 51 std::cout << "Calling export...\n"; 52 run.call(store, {}).unwrap(); 53 54 std::cout << "Done\n"; 55 } 56