title: What is a file with extension .a?
body: <p>I downloaded this: <a href="https://github.com/mongodb/mongo-c-driver" rel="noreferrer">https://github.com/mongodb/mongo-c-driver</a></p>
  
  <p>And now I'm trying to use it inside my C program, but I don't know what to do with the generated .a files. What are they? I couldn't find any information, not even in the GCC manual. </p>
  
  <p>And I built it like so: </p>
  
  <pre><code>  scons --c99
  </code></pre>
  
  <p>Also, can I use <a href="https://en.wikipedia.org/wiki/C99" rel="noreferrer">C99</a> libraries with my C89 program? </p>