Function template extract_or

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_value const & value, 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 excercised if the default value is a temporary object. Because the function returns a reference, if the temporary object is destroued, the reference may become dangling.

Parameters:

`def_val`	The default value
`value`	Attribute value.

Returns:

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