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   4       The standard exception classes carry with them a single string as
   5       data (usually describing what went wrong or where the 'throw' took
   6     place).  It's good to remember that you can add your own data to
   7     these exceptions when extending the hierarchy:
   8    </p><pre class="programlisting">
   9    struct My_Exception : public std::runtime_error
  10    {
  11      public:
  12        My_Exception (const string&amp; whatarg)
  13            : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
  14        int  errno_at_time_of_throw() const { return e; }
  15        DBID id_of_thing_that_threw() const { return id; }
  16      protected:
  17        int    e;
  18        DBID   id;     // some user-defined type
  19    };
  20    </pre></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="bk01pt03ch07.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="bk01pt03ch07.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="bk01pt03ch07s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 7. Exceptions </td><td width="20%" align="center"><a accesskey="h" href="../spine.html">Home</a></td><td width="40%" align="right" valign="top"> Cancellation</td></tr></table></div></body></html>