WebAssembly - Working with C++


In this chapter, we are going to compile a simple C++ program to javascript and execute the same in the browser.


C++ Program - Reversing a given number.

#include <iostream> 
int reversenumber(int n) { 
   int reverse=0, rem; 
   while(n!=0) { 
      rem=n%10; reverse=reverse*10+rem; n/=10; 
   return reverse; 

We have done the installation of emsdk in folder wa/. In same folder, create another folder cprog/ and save above code as reverse.cpp.

We have already installed emsdk in the previous chapter. Here, we are going to make use of emsdk to compile the above c code.

Compile test.c in your command prompt as shown below −

emcc reverse.cpp -s STANDALONE_WASM –o reverse.wasm

emcc command takes care of compiling the code as well as give you the .wasm code.

Example − reversenumber.html

<!doctype html> 
      <meta charset="utf-8">
      <title>WebAssembly Reverse Number</title>
         div { 
            font-size : 30px; text-align : center; color:orange; 
      <div id="textcontent"></div>
         let reverse; 
            .then(bytes => bytes.arrayBuffer()) 
            .then(mod => WebAssembly.compile(mod)) 
            .then(module => {return new WebAssembly.Instance(module) })
            .then(instance => { 
            reverse = instance.exports._Z13reversenumberi(1439898); 
            console.log("The reverse of 1439898 = " +reverse); 
               .innerHTML = "The reverse of 1439898 = " +reverse; 


The output is as follows −

Reverse Number HTML