<p>Class boost::<spanclass="RenoLink"><ahref="exception.html">exception</a></span> provides a virtual member function <spanclass="RenoLink"><ahref="exception_diagnostic_information.html">diagnostic_information</a></span>, with a signature similar to the familiar std::exception::what function. The default implementation returns a string value that is not presentable as a friendly user message, but because it is generated automatically, it is useful for debugging or logging purposes. Here is an example:</p>
<p>The <spanclass="RenoLink"><ahref="exception_diagnostic_information.html">diagnostic_information</a></span> member function iterates over all data objects stored in the boost::<spanclass="RenoLink"><ahref="exception.html">exception</a></span> through <spanclass="RenoLink"><ahref="operator_shl_exception.html">operator<<</a></span>. The returned string is constructed by converting each data object to string and then concatenating these strings together.</p>
<p>When the <spanclass="RenoLink"><ahref="error_info.html">error_info</a></span><Tag,T> template is instantiated, the system attempts overload resolution for an unqualified call to to_string(x), where x is of type T. If this is successful, the to_string overload is expected to return std::string and is used to convert objects of type T to string.</p>
<p>Otherwise, the system attempts overload resolution for s << x, where s is a std::ostringstream and x is of type T. If this is successful, the operator<< overload is used to convert objects of type T to string.</p>
<p>Otherwise the system is unable to convert objects of type T to string, and an unspecified stub string value is used without issuing a compile error.</p>
