...one of the most highly
regarded and expertly designed C++ library projects in the
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Coding Standards
boost::log::extract_or_default
// In header: <boost/log/attributes/value_extraction.hpp> template<typename DescriptorT, template< typename > class ActorT, typename DefaultT> result_of::extract_or_default< typenameDescriptorT::value_type, DefaultT, DescriptorT >::type extract_or_default(expressions::attribute_keyword< DescriptorT, ActorT > const & keyword, record const & rec, DefaultT const & def_val);
The function extracts an attribute value from the view. The user has to explicitly specify the type or set of possible types of the attribute value to be visited.
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Caution must be exercised if the default value is a temporary object. Because the function returns a reference, if the temporary object is destroyed, the reference may become dangling. |
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The extracted value, if found. The default value otherwise. |