title: Switch default c++ library from std=c++14 to std=c++17 on ubuntu
body: <p>I have tried to install a package on ubuntu that needs c++17 or newer libraries.
  I installed gcc-10 and g++-10. I also found that the default c++ library is c++14 by using this code:</p>
  <pre><code>man g++ | grep &quot;This is the default for C++ code&quot;
  </code></pre>
  <p>But I don't know how to change it to other versions.
  To run a simple code we can use <code>-std=c++17</code>. But I think Installing a package needs to change the default library.</p>