value_compare class

Provides a function object that can compare the elements of a hash_map by comparing the values of their keys to determine their relative order in the hash_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
    {
        return (comp(left.first, right.first));
    }

protected:
    value_compare(const key_compare& c) : comp (c) { }
    key_compare comp;
};

Remarks

Before removal, value_compare compared two hash_map elements by applying its stored key_compare object, comp, to their keys. It compared the first members of the elements rather than their mapped values.

For the legacy hash_set and hash_multiset containers, the key was also the element value, so value_compare was equivalent to key_compare. For the legacy hash_map and hash_multimap containers, the element was a pair, so the two comparison types weren't equivalent.

The standard unordered containers aren't direct replacements for this API. Because they don't order their elements, unordered_map, unordered_multimap, unordered_set, and unordered_multiset provide key_equal instead of value_compare or value_comp.

Example

See the example for hash_map::value_comp for an example of how to declare and use value_compare.

Requirements

Header: <hash_map>

Namespace: stdext

See also

binary_function Struct
Thread Safety in the C++ Standard Library
C++ Standard Library Reference