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Hello World

This chapter will take Hello World as an example to show how to compile a C program to WASM bytecode and run it in WasmEdge.


Before we start, make sure you have installed the following software:

  1. Install WasmEdge

  2. Emscripten, a toolchain for compiling C/C++ to WebAssembly. Please refer to the emcc official repository for detailed instructions.

git clone --depth 1
cd emsdk
./emsdk install latest
./emsdk activate latest
source ./

Example: Hello World

Compile the C code into Wasm

As the first step is always the "Hello World" program, given below is the C program implementation.

// hello.c

int main(int argc,char **argv){
printf("Hello World!\n");
return 0;

Save it in any file and then compile it to WebAssembly with emscripten.

emcc hello.c -o hello.wasm

Make sure you either supply -s STANDALONE_WASM flag or specify output as wasm -o your_file_name.wasm

Then run the wasm in wasmedge runtime.

$ wasmedge hello.wasm
Hello World

Run in WasmEdge

Run the compiled wasm with WasmEdge CLI, and you will get the hello world output.

$ wasmedge hello.wasm
Hello, world!

AoT mode

With WasmEdge's AoT compiler, you will get higher performance.

# Compile the wasm file with wasmedge aot compiler
$ wasmedgec hello.wasm hello.wasm
# Run the native binary with wasmedge
$ wasmedge hello.wasm

Example: Add function

We can also pass cmd arguments. For example, add function takes two arguments and prints their sum in this example.

// add.c

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
int a,b;
a = atoi(argv[1]);
b = atoi(argv[2]);
return 0;

Again Compiling to wasm with emcc

emcc add.c -o add.wasm

Running the application in wasmedge runtime

$ wasmedge add.wasm 2 3

We can further improve performance by using wasmedge AOT compilation , this feature gives near native performance

$ wasmedgec add.wasm add_aot.wasm
$ wasmedge add_aot.wasm 4 9

Example: Fibonacci function

We can also structure our project in separate header and implementation files.

// fibonacci.h

int fib(int n);
// fibonacci.c

#include <stdio.h>
#include "fibonacci.h"

int fib(int n){
int f1 = 0;
int f2 = 1;
if(n==1) return f1;
else return f2;
for(int i=2; i<n; i++ ){
int temp = f2;
return f2;
// main.c

#include <stdio.h>
#include <stdlib.h>
#include "fibonacci.h"

int main(int argc, char *argv[])
if (argc<2) {
return 0;
int n = atoi(argv[1]);
return 0;

Compiling the program to wasm with emcc

emcc main.c fibonacci.c -o fib.wasm

Running in wasmedge runtime

$ wasmedge fib.wasm 6