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 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);

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] 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:

def_val

The default value

keyword

The keyword of the attribute value to extract.

rec

A log record. The attribute value will be sought among those associated with the record.

Returns:

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


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