title: Compile-time error on declaration of `errno`
body: <p>During the process of compilation of my C++ program on Linux, it gives the following warning:</p>
  
  <pre><code>warning #584: omission of exception specification is incompatible with previous function "__errno_location" (declared at line 43 of "/usr/include/bits/errno.h")
  extern int errno;//error handling
           ^
  </code></pre>
  
  <p>The code is shown below:</p>
  
  <pre><code>#include &lt;errno.h&gt;    //for error handling
  #include &lt;cmath&gt;
  #include &lt;cstring&gt;
  #include &lt;ctime&gt;
  
  extern int errno;//error handling
  </code></pre>
  
  <p><code>errno</code> is a global variables, it is used in other <code>.cpp</code> files.  How can I solve this?</p>