title: ‘std::chrono::monotonic_clock’ has not been declared
body: <p>Does anyone know how to remove the error of <code>std::chrono::monotonic_clock</code> in Linux OS (Ubuntu 14.04)? I have the headers of <code>chrono</code>, <code>time</code> ,<code>unistd.h</code> <code>stdio.h</code> but the same error shows up.</p>