io_service deadline timer does not work periodically - c++

Question

i want to make a timer with 10s periodically in the class inside, but it does not work. It will print count in 10s at the first time. But after that, it does not wait another 10s. the specific code.
#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
class test {
boost::asio::io_service& a;
boost::asio::deadline_timer t;
int count;
void print(const boost::system::error_code& /*e*/)
{
while(true)
{
std::cout << count << " ";
++(count);
t.expires_at(t.expires_at() + boost::posix_time::seconds(10));
t.async_wait(boost::bind(&test::print, this, boost::asio::placeholders::error));
}
}
public:
test(boost::asio::io_service& io) : a(io), t(io, boost::posix_time::seconds(10)) {
count = 0;
};
void start() {
t.async_wait(boost::bind(&test::print, this, boost::asio::placeholders::error));
}
};
int main()
{
boost::asio::io_service io;
int count = 0;
test b(io);
b.start();
io.run();
return 0;
}

Answer 1

Your print() function has an unnecessary while(true) loop. Once we remove that, we notice that the output doesn't come right away; that's because std::cout is line-buffered and we never write a newline. Here's the full fixed function:
void print(const boost::system::error_code& /*e*/)
{
std::cout << count << " " << std::flush;
++(count);
t.expires_at(t.expires_at() + boost::posix_time::seconds(10));
t.async_wait(boost::bind(&test::print, this, boost::asio::placeholders::error));
}