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	<title>integrating boost exception in existing exception class hierarchies</title>
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<h1>Boost Exception</h1>
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<!-- Copyright (c) 2006-2009 Emil Dotchevski and Reverge Studios, Inc. -->
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<div class="RenoIncludeDIV"><div class="RenoAutoDIV"><h2>Integrating Boost Exception in Existing Exception Class Hierarchies</h2>
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<p>Some exception hierarchies can not be modified to make boost::<span class="RenoLink"><a href="exception.html">exception</a></span> a base type. In this case, the <span class="RenoLink"><a href="enable_error_info.html">enable_error_info</a></span> function template can be used to make exception objects derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span> anyway. Here is an example:</p>
<pre>#include &lt;<span class="RenoLink"><a href="boost_exception_all_hpp.html">boost/exception/all.hpp</a></span>&gt;
#include &lt;stdexcept&gt;

typedef boost::<span class="RenoLink"><a href="error_info.html">error_info</a></span>&lt;struct tag_std_range_min,size_t&gt; std_range_min;
typedef boost::<span class="RenoLink"><a href="error_info.html">error_info</a></span>&lt;struct tag_std_range_max,size_t&gt; std_range_max;
typedef boost::<span class="RenoLink"><a href="error_info.html">error_info</a></span>&lt;struct tag_std_range_index,size_t&gt; std_range_index;

template &lt;class T&gt;
class
my_container
    {
    public:

    size_t size() const;

    T const &amp;
    operator[]( size_t i ) const
        {
        if( i &gt; size() )
            throw boost::<span class="RenoLink"><a href="enable_error_info.html">enable_error_info</a></span>(std::range_error("Index out of range")) &lt;&lt;
                std_range_min(0) &lt;&lt;
                std_range_max(size()) &lt;&lt;
                std_range_index(i);
        //....
        }
    };
</pre>
<p>The call to <span class="RenoLink"><a href="enable_error_info.html">enable_error_info</a></span>&lt;T&gt; gets us an object of <i>unspecified type</i> which is guaranteed to derive from both boost::<span class="RenoLink"><a href="exception.html">exception</a></span> and T. This makes it possible to use <span class="RenoLink"><a href="exception_operator_shl.html">operator&lt;&lt;</a></span> to store additional information in the exception object. The exception can be intercepted as T &amp;, so existing exception handling will not break. It can also be intercepted as boost::<span class="RenoLink"><a href="exception.html">exception</a></span> &amp;, so that <span class="RenoLink"><a href="tutorial_transporting_data.html">more information can be added to the exception at a later time</a></span>.</p>
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See also: <span class="RenoPageList"><a href="boost-exception.html">Boost Exception</a>&nbsp;| <a href="motivation.html">Motivation</a></span>
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<small>Copyright (c) 2006-2009 by Emil Dotchevski and Reverge Studios, Inc.<br/>
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