How to use lambda to for boost asio async completion handler

#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>

void print(boost::asio::deadline_timer* t, int* count)
    if (*count < 5)
        std::cout << *count << "\n";

        t->expires_at(t->expires_at() + boost::posix_time::seconds(1));
        t->async_wait(boost::bind(print, t, count));

int main()
    boost::asio::io_service io;

    int count = 0;
    boost::asio::deadline_timer t(io, boost::posix_time::seconds(1));
//    t.async_wait(boost::bind(print, &t, &count));
    t.async_wait([&]{ // compile error occurred
        print(&t, &count);

    std::cout << "Final count is " << count << "\n";

    return 0;

What's the different between bind and lambda exp.? I guess it's OK in syntax, the problem is async_wait need a function object with param "const boost::system::error_code& e".


I don't know asio very well, but adding the requested parameter fixes the issue.

t.async_wait([&] ( const boost::system::error_code& ) {
    print(&t, &count);

It looks like a quirk or bug of Boost.Bind allows additional, ignored arguments to a bind expression generated from a function pointer. It's probably better not to rely on this, but to explicitly accept and discard the error code.

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