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boost::log::extract_or_default
// In header: <boost/log/attributes/value_extraction.hpp> template<typename T, typename TagT = void, typename DefaultT> result_of::extract_or_default< T, DefaultT, TagT >::type extract_or_default(attribute_name const & name, attribute_value_set const & attrs, 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 extracted.
| ![[Note]](../../../../../../doc/src/images/note.png) | Note | 
|---|---|
| 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. | 
| Parameters: | 
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| Returns: | The extracted value, if found. The default value otherwise. |