title: what are the commonly used libc header files and their functionalities
body: <p>I have searched a lot and found a beautiful reference of <a href="https://en.wikipedia.org/wiki/C_standard_library" rel="nofollow">https://en.wikipedia.org/wiki/C_standard_library</a> different header files, but it doesn't say anything about the common functions they define. Is there any brief reference to commonly used C functions?</p>
  
  <p>For example:</p>
  
  <pre><code>#include &lt;getopt.h&gt;
  #include &lt;event.h&gt;
  #include &lt;libpq-fe.h&gt;
  #include &lt;config.h&gt;
  #include &lt;stdio.h&gt;
  #include &lt;sys/types.h&gt;
  #include &lt;sys/utsname.h&gt;
  #include &lt;pwd.h&gt;
  #include &lt;grp.h&gt;
  </code></pre>
  
  <p>..are headers which I see commonly on major c programs..  Can anyone explain what they do?</p>
  
  <ul>
  <li><p>Nb : if i see a method int XXX(char *YYY) , how can i find in which header this method is defined .. </p></li>
  </ul>