C++

参考

<set>

multiset

public member function
<set>

std::multiset::key_comp

key_compare key_comp() const;
Return comparison object
Returns a copy of the comparison object used by the container.

By default, this is a less object, which returns the same asoperator<.

This object determines the order of the elements in the container: it is a function pointer or a function object that takes two arguments of the same type as the container elements, and returnstrueif the first argument is considered to go before the second in the strict weak ordering it defines, andfalse否则为 false。

Two elements of a multiset are considered equivalent ifkey_comp返回 11。falsereflexively (i.e., no matter the order in which the elements are passed as arguments).

In multiset containers, the keys to sort the elements are the values themselves, thereforekey_compand its sibling member function value_comp are equivalent.

参数

无

返回值

The comparison object.
成员类型key_compareis the type of the comparison object associated to the container, defined in multiset as an alias of its second template parameter (Compare).

示例

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// multiset::key_comp
#include <iostream>
#include <set>

int main ()
{
  std::multiset<int> mymultiset;

  for (int i=0; i<5; i++) mymultiset.insert(i);

  std::multiset<int>::key_compare mycomp = mymultiset.key_comp();

  std::cout << "mymultiset contains:";

  int highest = *mymultiset.rbegin();

  std::multiset<int>::iterator it = mymultiset.begin();
  do {
    std::cout << ' ' << *it;
  } while ( mycomp(*it++,highest) );

  std::cout << '\n';

  return 0;
}

输出
mymultiset contains: 0 1 2 3 4


复杂度

常量。

迭代器有效性

没有变化。

数据竞争

访问容器。
同时访问 multiset 的元素是安全的。

异常安全

强保证：如果抛出异常，容器没有发生变化。

另见

multiset::value_comp
返回比较对象 （公开成员函数）
multiset::find
获取指向元素的迭代器 (公共成员函数)
multiset::count
计算具有特定键的元素数量 (公共成员函数)
multiset::lower_bound
返回指向下界的迭代器 （公开成员函数）
multiset::upper_bound
返回指向上界的迭代器 （公开成员函数）