File stream constructor
<p>File stream class cannot accept <code>string</code> as argument of its construtor, only C-string. </p>

<pre><code>char fname[] = "file";
string fname_string ("file");
ifstream ifs (fname); //OK
ifstream ifs (fname_string); //Error
</code></pre>

<p>Why is it so? Is there any sense in that? </p>
