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Socket.IO C++ Client

Build Status

By virtue of being written in C++, this client works in several different platforms. The examples folder contains an iPhone, QT and Console example chat client! It depends on websocket++ and is inspired by

Clients with iPhone, QT, Console and web

Compatibility table

C++ Client version Socket.IO server version
1.x / 2.x 3.x / 4.x
2.x (2.x branch) YES YES, with allowEIO3: true
3.x (master branch) NO YES


  • 100% written in modern C++11
  • Binary support
  • Automatic JSON encoding
  • Multiplex support
  • Similar API to the Socket.IO JS client
  • Cross platform

Note: Only the WebSocket transport is currently implemented (no fallback to HTTP long-polling)

Installation alternatives


** Full overview of API can be seen here **

The APIs are similar to the JS client.

Connect to a server

sio::client h;

Emit an event

// emit event name only:

// emit text
h.socket()->emit("add user", username);

// emit binary
char buf[100];
h.socket()->emit("add user", std::make_shared<std::string>(buf,100));

// emit message object with lambda ack handler
h.socket()->emit("add user", string_message::create(username), [&](message::list const& msg) {

// emit multiple arguments
message::list li("sports");
socket->emit("categories", li);

Items in message::list will be expanded in server side event callback function as function arguments.

Bind an event

Bind with function pointer
void OnMessage(sio::event &)

h.socket()->on("new message", &OnMessage);
Bind with lambda
h.socket()->on("login", [&](sio::event& ev)
    //handle login message
    //post to UI thread if any UI updating.
Bind with member function
class MessageHandler
    void OnMessage(sio::event &);
MessageHandler mh;
h.socket()->on("new message",std::bind( &MessageHandler::OnMessage,&mh,std::placeholders::_1));

Using namespace

h.socket("/chat")->emit("add user", username);

** Full overview of API can be seen here **