1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Struct template fallback_to_default</title> 5<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../index.html" title="Chapter 1. Boost.Log v2"> 8<link rel="up" href="../../attributes.html#header.boost.log.attributes.fallback_policy_fwd_hpp" title="Header <boost/log/attributes/fallback_policy_fwd.hpp>"> 9<link rel="prev" href="fallback_to_throw.html" title="Struct fallback_to_throw"> 10<link rel="next" href="attributes/function.html" title="Class template function"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td></tr></table> 14<hr> 15<div class="spirit-nav"> 16<a accesskey="p" href="fallback_to_throw.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../attributes.html#header.boost.log.attributes.fallback_policy_fwd_hpp"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="attributes/function.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 17</div> 18<div class="refentry"> 19<a name="boost.log.fallback_to_default"></a><div class="titlepage"></div> 20<div class="refnamediv"> 21<h2><span class="refentrytitle">Struct template fallback_to_default</span></h2> 22<p>boost::log::fallback_to_default</p> 23</div> 24<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2> 25<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: <<a class="link" href="../../attributes.html#header.boost.log.attributes.fallback_policy_fwd_hpp" title="Header <boost/log/attributes/fallback_policy_fwd.hpp>">boost/log/attributes/fallback_policy_fwd.hpp</a>> 26 27</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> DefaultT<span class="special">></span> 28<span class="keyword">struct</span> <a class="link" href="fallback_to_default.html" title="Struct template fallback_to_default">fallback_to_default</a> <span class="special">{</span> 29 <span class="comment">// <a class="link" href="fallback_to_default.html#boost.log.fallback_to_defaultconstruct-copy-destruct">construct/copy/destruct</a></span> 30 <a class="link" href="fallback_to_default.html#idm46079579336032-bb"><span class="identifier">fallback_to_default</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 31 <span class="keyword">explicit</span> <a class="link" href="fallback_to_default.html#idm46079579335328-bb"><span class="identifier">fallback_to_default</span></a><span class="special">(</span><span class="identifier">default_type</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 32 33 <span class="comment">// <a class="link" href="fallback_to_default.html#idm46079579343024-bb">public member functions</a></span> 34 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> FunT<span class="special">></span> <span class="keyword">bool</span> <a class="link" href="fallback_to_default.html#idm46079579342464-bb"><span class="identifier">apply_default</span></a><span class="special">(</span><span class="identifier">FunT</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 35 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> FunT<span class="special">></span> <span class="keyword">bool</span> <a class="link" href="fallback_to_default.html#idm46079579339328-bb"><span class="identifier">apply_default</span></a><span class="special">(</span><span class="identifier">FunT</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 36 37 <span class="comment">// <a class="link" href="fallback_to_default.html#idm46079579333648-bb">public static functions</a></span> 38 <span class="keyword">static</span> <span class="keyword">void</span> <a class="link" href="fallback_to_default.html#idm46079579333088-bb"><span class="identifier">on_invalid_type</span></a><span class="special">(</span><span class="identifier">typeindex</span><span class="special">::</span><span class="identifier">type_index</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 39 <span class="keyword">static</span> <span class="keyword">void</span> <a class="link" href="fallback_to_default.html#idm46079579330752-bb"><span class="identifier">on_missing_value</span></a><span class="special">(</span><span class="special">)</span><span class="special">;</span> 40<span class="special">}</span><span class="special">;</span></pre></div> 41<div class="refsect1"> 42<a name="idm44984882925936"></a><h2>Description</h2> 43<p>The <code class="computeroutput"><a class="link" href="fallback_to_default.html" title="Struct template fallback_to_default">fallback_to_default</a></code> policy results in a default value if the attribute value cannot be extracted. </p> 44<div class="refsect2"> 45<a name="idm44984882923856"></a><h3> 46<a name="boost.log.fallback_to_defaultconstruct-copy-destruct"></a><code class="computeroutput">fallback_to_default</code> 47 public 48 construct/copy/destruct</h3> 49<div class="orderedlist"><ol class="orderedlist" type="1"> 50<li class="listitem"> 51<pre class="literallayout"><a name="idm46079579336032-bb"></a><span class="identifier">fallback_to_default</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> 52<p>Default constructor. </p> 53</li> 54<li class="listitem"> 55<pre class="literallayout"><span class="keyword">explicit</span> <a name="idm46079579335328-bb"></a><span class="identifier">fallback_to_default</span><span class="special">(</span><span class="identifier">default_type</span> <span class="keyword">const</span> <span class="special">&</span> def_val<span class="special">)</span><span class="special">;</span></pre> 56<p>Initializing constructor. </p> 57</li> 58</ol></div> 59</div> 60<div class="refsect2"> 61<a name="idm44984882910960"></a><h3> 62<a name="idm46079579343024-bb"></a><code class="computeroutput">fallback_to_default</code> public member functions</h3> 63<div class="orderedlist"><ol class="orderedlist" type="1"> 64<li class="listitem"> 65<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> FunT<span class="special">></span> <span class="keyword">bool</span> <a name="idm46079579342464-bb"></a><span class="identifier">apply_default</span><span class="special">(</span><span class="identifier">FunT</span> <span class="special">&</span> fun<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> 66<p>The method is called in order to apply a function object to the default value. </p> 67</li> 68<li class="listitem"> 69<pre class="literallayout"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> FunT<span class="special">></span> <span class="keyword">bool</span> <a name="idm46079579339328-bb"></a><span class="identifier">apply_default</span><span class="special">(</span><span class="identifier">FunT</span> <span class="keyword">const</span> <span class="special">&</span> fun<span class="special">)</span> <span class="keyword">const</span><span class="special">;</span></pre> 70<p>The method is called in order to apply a function object to the default value. </p> 71</li> 72</ol></div> 73</div> 74<div class="refsect2"> 75<a name="idm44984882889456"></a><h3> 76<a name="idm46079579333648-bb"></a><code class="computeroutput">fallback_to_default</code> public static functions</h3> 77<div class="orderedlist"><ol class="orderedlist" type="1"> 78<li class="listitem"> 79<pre class="literallayout"><span class="keyword">static</span> <span class="keyword">void</span> <a name="idm46079579333088-bb"></a><span class="identifier">on_invalid_type</span><span class="special">(</span><span class="identifier">typeindex</span><span class="special">::</span><span class="identifier">type_index</span> <span class="keyword">const</span> <span class="special">&</span><span class="special">)</span><span class="special">;</span></pre> 80<p>The method is called when value extraction failed because the attribute value has different type than requested. </p> 81</li> 82<li class="listitem"> 83<pre class="literallayout"><span class="keyword">static</span> <span class="keyword">void</span> <a name="idm46079579330752-bb"></a><span class="identifier">on_missing_value</span><span class="special">(</span><span class="special">)</span><span class="special">;</span></pre> 84<p>The method is called when value extraction failed because the attribute value was not found. </p> 85</li> 86</ol></div> 87</div> 88</div> 89</div> 90<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 91<td align="left"></td> 92<td align="right"><div class="copyright-footer">Copyright © 2007-2019 Andrey Semashev<p> 93 Distributed under the Boost Software License, Version 1.0. (See accompanying 94 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>). 95 </p> 96</div></td> 97</tr></table> 98<hr> 99<div class="spirit-nav"> 100<a accesskey="p" href="fallback_to_throw.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../attributes.html#header.boost.log.attributes.fallback_policy_fwd_hpp"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="attributes/function.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 101</div> 102</body> 103</html> 104
