Boost C++ Libraries

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Function template extract_or_default

boost::log::extract_or_default

Synopsis

// 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, record const & rec, 
                     DefaultT const & def_val);

Description

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.

	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:

`name`	The name of the attribute value to extract.
`rec`	A log record. The attribute value will be sought among those associated with the record.
`def_val`	The default value

Returns:

The extracted value, if found. The default value otherwise.