I am writing code to create an online c++ piler in node.js environment.Using spawn function i created a child process which will pile the code and execute it and send the output back to the user. But i need to send input to the running c++ program . I used child.stdin.write('data'); for sending data to child but i think cin in the program is not receiving the input .
Please help me to send the input to the running c++ code.
Thanks.

I am writing code to create an online c++ piler in node.js environment.Using spawn function i created a child process which will pile the code and execute it and send the output back to the user. But i need to send input to the running c++ program . I used child.stdin.write('data'); for sending data to child but i think cin in the program is not receiving the input .
Please help me to send the input to the running c++ code.
Thanks.

• javascript
• c++
• node.js
• online-pilation

Share Improve this question Follow edited Nov 21, 2014 at 0:34 Sri Harsha asked Nov 20, 2014 at 22:50 Sri HarshaSri Harsha 66122 gold badges88 silver badges1919 bronze badges 1

• just in case someone is using IPC and JSON serialization, what I observed is that it sends message from Child-to-Parent but not Parent-to-Child using send() function. When I used fork instead of spawn, it started sending messages in both ways. – Ankur Thakur Commented Apr 27, 2023 at 14:06

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2 Answers 2

Sorted by: Reset to default 4

1.Create a file with input data.
2.Create a ReadStream opening input file.
3.Pipe the ReadStream with childprocess.stdin.

file=fs.createReadStream('input.txt',{encoding:'utf8'});
file.pipe(childprocess.stdin);

This worked for me .

You should probably use either cluster, or fork if you want to pass messages... if you do this, node will setup IPC for you to be able to municate via process.send

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Alternatively, you could use a pub/sub system for munication channels (Redis works well for this), this is also your best bet if you need munications across servers.

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Below is an example of an older work script...

var env = process.env.NODE_ENV || 'dev';
var cluster = require("cluster");

//TODO: need to adjust to use domains for this work
process.on('uncaughtException', function (err) {
  console.error('GENERAL EXCEPTION IN %s: %s', process.env.WORKER_TYPE || 'MASTER',err);
  if (err.stack) console.error(err.stack);
  if (cluster.isWorker) {
    //process.send notifies the parent process of the error
    process.send({
      err: {
        "str": err && err.toString() || "unknown error"
        ,"message": err && err.message || null
        ,"stack": err && err.stack || null
      }
    });
  }
  process.nextTick(function(){
    process.exit(666);
  });
});


if (cluster.isMaster) startMaster();
if (cluster.isWorker) startWorker();

function startMaster() {
  createWorker("foo");
  createWorker("bar");
}

function createWorker(workerType) {
  var worker = cluster.fork({"WORKER_TYPE":workerType}); //passes environment variables to child
  worker.on('online',onOnline.bind(null, worker));
  worker.on('message',onMessage.bind(null, worker)); 
  worker.on('exit',onExit.bind(null, worker));
  worker.workerType = workerType;
  return worker; 
  // you can use worker.send() to send a message that 
  // will raise a message event in the child
}

function startWorker() {
  console.log("Running Worker: %s %s", cluster.worker.id, process.env.WORKER_TYPE);
  setTimeout(process.exit.bind(process,0), 5000); //close in 5 seconds
  //you may want to load a specific module based on WORKER_TYPE
}

function onOnline(worker) {
  console.log("Worker Online: %s %s", worker.id, worker.workerType);
  //console.log(arguments);
}

function onMessage(worker, msg) {
  if (msg.err) {
    console.warn("Error From", worker.id, worker.workerType, msg.err);
  } else {
    console.log("Message From", worker.id, worker.workerType);
  }
  //console.log(arguments);
}

function onExit(worker, code, signal) {
  console.log("Worker Exited: %s %s %s %s", worker.id, worker.workerType, code, signal);

    if (env == 'dev') {
        //for now just exit the whole thing (dev mode)
        process.nextTick(function(){
            process.exit(1);
        });
    } else {
        //workers should simply keep working...
        //fire off a new worker
        createWorker(worker.workerType);
    }

}