compiled libraries vs header only libraries
<p>I am newish to C++ and I am trying to understand why some libraries need to be compiled first.</p>

<p>For example some boost libraries are header only (e.g. msm) some others need to be compiled (e.g timer)</p>

<p>I can't find a nice explanation for why is this so. Can someone help me understand?</p>

<p>Thank you</p>
