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| <a name="log.rationale.why_attribute_manips_dont_affect_filters"></a><a class="link" href="why_attribute_manips_dont_affect_filters.html" title="Why attributes set with stream manipulators do not participate in filtering?">Why |
| attributes set with stream manipulators do not participate in filtering?</a> |
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| One can add attributes to log records in the following way: |
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| <pre class="programlisting"><span class="identifier">BOOST_LOG</span><span class="special">(</span><span class="identifier">logger</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">add_value</span><span class="special">(</span><span class="string">"MyInt"</span><span class="special">,</span> <span class="number">10</span><span class="special">)</span> <span class="special"><<</span> <span class="identifier">logging</span><span class="special">::</span><span class="identifier">add_value</span><span class="special">(</span><span class="string">"MyString"</span><span class="special">,</span> <span class="string">"string attribute value"</span><span class="special">)</span> |
| <span class="special"><<</span> <span class="string">"Some log message"</span><span class="special">;</span> |
| </pre> |
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| However, filters will not be able to use MyInt and MyString attributes. The |
| reason for this behavior is quite simple. The streaming expression is executed |
| <span class="emphasis"><em>after</em></span> the filtering takes place and only <span class="emphasis"><em>if</em></span> |
| the filter passed the log record. At this point these attributes have not |
| been added to the record yet. The easiest way to pass attributes to the filter |
| is to use scoped attributes or tags (see <a class="link" href="../detailed/attributes.html#log.detailed.attributes.related_components.scoped_attributes" title="Scoped attributes">here</a>). |
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| <td align="right"><div class="copyright-footer">Copyright © 2007-2015 Andrey |
| Semashev<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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>). |
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