value_compare
Class (<map>
)
Provides a function object that can compare the elements of a map by comparing the values of their keys to determine their relative order in the map.
Syntax
class value_compare : public binary_function<value_type, value_type, bool>
{
public:
bool operator()(const value_type& left, const value_type& right) const;
value_compare(key_compare pred) : comp(pred);
protected:
key_compare comp;
};
Remarks
The comparison criterion provided by value_compare
between value_types
of whole elements contained by a map is induced from a comparison between the keys of the respective elements by the auxiliary class construction. The member function operator uses the object comp
of type key_compare
stored in the function object provided by value_compare
to compare the sort-key components of two elements.
For sets and multisets, which are simple containers where the key values are identical to the element values, value_compare
is equivalent to key_compare
; for maps and multimaps they are not, as the value of the type pair
elements is not identical to the value of the element's key.
Example
See example for value_comp for an example of how to declare and use value_compare
.
Requirements
Header: <map>
Namespace: std
See also
binary_function Struct
Thread Safety in the C++ Standard Library
C++ Standard Library Reference
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