title: error C2065: 'errno' : undeclared identifier in <string> in Visual Studio 2012
body: <p>I had a project running in <code>Visual Studio 2010</code>. Now I am using <code>Visual Studio 2012</code>.
  Now I am getting below error while building the project.
  I have looked into <code>Google</code> and <code>SO</code> as well. But no where I got any solution.</p>
  
  <pre><code>    c:\program files\microsoft visual studio 11.0\vc\include\string(557): error C2065: 'errno' : undeclared identifier
  2&gt;c:\program files\microsoft visual studio 11.0\vc\include\string(557): error C2065: 'errno' : undeclared identifier
  2&gt;c:\program files\microsoft visual studio 11.0\vc\include\string(562): error C2065: 'errno' : undeclared identifier
  2&gt;c:\program files\microsoft visual studio 11.0\vc\include\string(574): error C2065: 'errno' : undeclared identifier
  2&gt;c:\program files\microsoft visual studio 11.0\vc\include\string(579): error C2065: 'errno' : undeclared identifier
  </code></pre>
  
  <p>I have tried with including <code>stdlib.h</code> into the <code>sting</code> header file but still I am getting this same error.</p>
  
  <p>Any help appreciated.</p>