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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Adding Data to Exceptions</title><meta name="generator" content="DocBook XSL Stylesheets V1.73.2" /><meta name="keywords" content="&#10;      ISO C++&#10;    , &#10;      library&#10;    " /><link rel="start" href="../spine.html" title="The GNU C++ Library Documentation" /><link rel="up" href="bk01pt03ch07.html" title="Chapter 7. Exceptions" /><link rel="prev" href="bk01pt03ch07.html" title="Chapter 7. Exceptions" /><link rel="next" href="bk01pt03ch07s03.html" title="Cancellation" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Adding Data to Exceptions</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="bk01pt03ch07.html">Prev</a> </td><th width="60%" align="center">Chapter 7. Exceptions</th><td width="20%" align="right"> <a accesskey="n" href="bk01pt03ch07s03.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.diagnostics.exceptions.data"></a>Adding Data to Exceptions</h2></div></div></div><p>
      The standard exception classes carry with them a single string as
      data (usually describing what went wrong or where the 'throw' took
    place).  It's good to remember that you can add your own data to
    these exceptions when extending the hierarchy:
   </p><pre class="programlisting">
   struct My_Exception : public std::runtime_error
   {
     public:
       My_Exception (const string&amp; whatarg)
           : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
       int  errno_at_time_of_throw() const { return e; }
       DBID id_of_thing_that_threw() const { return id; }
     protected:
       int    e;
       DBID   id;     // some user-defined type
   };
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