title: What's the differences between -m32, -m64, and nothing in gcc's options?
body: <pre><code>gcc -m32 main.cpp
  
  gcc -m64 main.cpp
  
  gcc main.cpp
  </code></pre>
  
  <p>What's the differences between <code>-m32</code>, <code>-m64</code>, and <code>nothing</code> in gcc's options?</p>