exception/doc/logging.html

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<!-- Copyright (c) 2006-2008 Emil Dotchevski and Reverge Studios, Inc. -->
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<div class="RenoIncludeDIV"><h2>Logging of boost::exception Objects</h2>
<p>Class <tt>boost::<span class="RenoLink"><a href="exception.html">exception</a></span></tt> provides a virtual member function <tt><span class="RenoLink"><a href="exception_what.html">what</a></span>()</tt>, with a signature identical to the familiar <tt>std::exception::what()</tt> 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>
<pre>#include &lt;<span class="RenoLink"><a href="exception_hpp.html">boost/exception.hpp</a></span>&gt;
#include &lt;iostream&gt;

void f(); //throws unknown types that derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>.

void
g()
    {
    try
        {
        f();
        }
    catch(
    boost::<span class="RenoLink"><a href="exception.html">exception</a></span> &amp; e )
        {
        std::cerr &lt;&lt; e.<span class="RenoLink"><a href="exception_what.html">what</a></span>();
        }
    }</pre>
<p>The <tt><span class="RenoLink"><a href="exception_what.html">what</a></span>()</tt> member function iterates over all data objects stored in the <tt>boost::<span class="RenoLink"><a href="exception.html">exception</a></span></tt> through <tt><span class="RenoLink"><a href="operator_shl_exception.html">operator&lt;&lt;</a></span>()</tt>. The returned string is constructed by converting each data object to string and then concatenating these strings together.</p>
<p>When the <tt><span class="RenoLink"><a href="error_info.html">error_info</a></span>&lt;Tag,T&gt;</tt> template is instantiated, the system attempts overload resolution for an unqualified call to <tt>to_string(x)</tt>, where <tt>x</tt> is of type <tt>T</tt>. If this is successful, the <tt>to_string()</tt> overload is used to convert objects of type <tt>T</tt> to string.</p>
<p>Otherwise, the system attempts overload resolution for <tt>s &lt;&lt; x</tt>, where <tt>s</tt> is a <tt>std::ostringstream</tt> and <tt>x</tt> is of type <tt>T</tt>. If this is successful, the <tt>operator&lt;&lt;</tt> overload is used to convert objects of type <tt>T</tt> to string.</p>
<p>Otherwise the system is unable to convert objects of type <tt>T</tt> to string, and an unspecified stub string value is used without issuing a compile error.</p>
</div><h3>See also:</h3>
<div class="RenoPageList"><a href="boost-exception.html">Boost Exception<br/>
</a></div>
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boost exception [SVN r43485] 2008-03-04 01:41:17 +00:00			`<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Strict//EN'`
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			`<h1>Boost Exception</h1>`
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minor documentation fixes. [SVN r44476] 2008-04-16 22:55:19 +00:00			`<!-- Copyright (c) 2006-2008 Emil Dotchevski and Reverge Studios, Inc. -->`
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boost exception [SVN r43485] 2008-03-04 01:41:17 +00:00			`<div class="RenoIncludeDIV"><h2>Logging of boost::exception Objects</h2>`
			<p>Class <tt>boost::<span class="RenoLink"><a href="exception.html">exception</a></span></tt> provides a virtual member function <tt><span class="RenoLink"><a href="exception_what.html">what</a></span>()</tt>, with a signature identical to the familiar <tt>std::exception::what()</tt> 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>
			`<pre>#include <<span class="RenoLink"><a href="exception_hpp.html">boost/exception.hpp</a></span>>`
			`#include <iostream>`

			`void f(); //throws unknown types that derive from boost::<span class="RenoLink"><a href="exception.html">exception</a></span>.`

			`void`
			`g()`
			`{`
			`try`
			`{`
			`f();`
			`}`
			`catch(`
			`boost::<span class="RenoLink"><a href="exception.html">exception</a></span> & e )`
			`{`
			`std::cerr << e.<span class="RenoLink"><a href="exception_what.html">what</a></span>();`
			`}`
			`}</pre>`
			`<p>The <tt><span class="RenoLink"><a href="exception_what.html">what</a></span>()</tt> member function iterates over all data objects stored in the <tt>boost::<span class="RenoLink"><a href="exception.html">exception</a></span></tt> through <tt><span class="RenoLink"><a href="operator_shl_exception.html">operator<<</a></span>()</tt>. The returned string is constructed by converting each data object to string and then concatenating these strings together.</p>`
			`<p>When the <tt><span class="RenoLink"><a href="error_info.html">error_info</a></span><Tag,T></tt> template is instantiated, the system attempts overload resolution for an unqualified call to <tt>to_string(x)</tt>, where <tt>x</tt> is of type <tt>T</tt>. If this is successful, the <tt>to_string()</tt> overload is used to convert objects of type <tt>T</tt> to string.</p>`
			`<p>Otherwise, the system attempts overload resolution for <tt>s << x</tt>, where <tt>s</tt> is a <tt>std::ostringstream</tt> and <tt>x</tt> is of type <tt>T</tt>. If this is successful, the <tt>operator<<</tt> overload is used to convert objects of type <tt>T</tt> to string.</p>`
			`<p>Otherwise the system is unable to convert objects of type <tt>T</tt> to string, and an unspecified stub string value is used without issuing a compile error.</p>`
			`</div><h3>See also:</h3>`
			`<div class="RenoPageList"><a href="boost-exception.html">Boost Exception<br/>`
			`</a></div>`
minor documentation fixes. [SVN r44476] 2008-04-16 22:55:19 +00:00			`<!-- Copyright (c) 2006-2008 Emil Dotchevski and Reverge Studios, Inc. -->`
			`<!-- Distributed under the Boost Software License, Version 1.0. (See accompanying -->`
			`<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->`
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