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    <p>I finally found the culprit. If you search for Internet a lot of sites recommends using the sync_with_stdio call, but they don't talk about threads.</p> <p>Other sites talk about iostreams and threads, like <a href="https://stackoverflow.com/questions/6374264/is-cout-synchronized-thread-safe">this one</a>, but that doesn't explain why I was getting corrupted output when I was using std::cin in <strong>only one thread</strong>, and std::cout <strong>in its own thread too</strong>.</p> <p>The problem is that internally, the std::cin input thread was calling to std::cout to flush its buffer, but as the streams where not synchronized with mutex or something similar, the output was corrupted. Why should I synchronized the buffers if they are doing different things? Why std::cin was messing with std::cout?</p> <p>In C++, by default, the standard streams cin, cerr and clog are tied to cout. What does this mean? It means that when you try to read from cin, first it will force a flush to cout. Sometimes this is something useful as you can read <a href="https://stackoverflow.com/questions/2704752/flushing-of-cout-prior-to-reading-input-using-cin-why">here</a>.</p> <p>But in my case, this was causing some serious issues, so, how to untie the streams?. It's very easy using the <a href="http://en.cppreference.com/w/cpp/io/basic_ios/tie" rel="nofollow noreferrer"><strong>tie method</strong></a>:</p> <pre><code>std::ios_base::sync_with_stdio(false); std::cin.tie(nullptr); std::cerr.tie(nullptr); </code></pre> <p>Or if your compiler doesn't support C++11:</p> <pre><code>std::ios_base::sync_with_stdio(false); std::cin.tie(static_cast&lt;ostream*&gt;(0)); std::cerr.tie(static_cast&lt;ostream*&gt;(0)); </code></pre> <p>With this changes my output it's now correct:</p> <pre><code>Packet id = 1 Packet id = 2 Packet id = 3 Packet id = 4 Packet id = 5 Packet id = 6 Packet id = 7 Packet id = 8 Packet id = 9 Packet id = 10 </code></pre> <p>And as it avoids doing a flush every time std::cin is used, it's faster too :-)</p>
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    1. COGood catch. So the fflush of stdout is there because many people do: `cout << "What's your name?"; cin >> name;`, and will be confused when there is no output. Some C libraries don't have the "flush before read", which causes at least beginners to get confused.
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    2. CO+1 good answer to your own question.
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    3. COBTW, you don't need explicit cast `static_cast<ostream*>(0);`. You just could pass `0` as `std::cin.tie(0);`, and you should also save the returned stream, so when you're done, you could `tie` it to the stream.
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