1、简介

multiset跟set具有相同功能，但允许重复的元素。multiset容器的内部结构通常由平衡二叉树(balanced binary tree)来实现。当元素放入容器中时，会按照一定的排序法则自动排序，默认是按照less<>排序规则来排序。这种自动排序的特性加速了元 素查找的过程，但是也带来了一个问题：不可以直接修改set或multiset容器中的元素值，因为这样做就可能违反了元素自动排序的规则。如果你希望修 改一个元素的值，必须先删除原有的元素，再插入新的元素。

2、成员函数

2.1 构造函数

multiset( );

explicit multiset (

const Compare& _Comp

);

multiset (

const Compare& _Comp,

const Allocator& _Al

);

set(

const multiset<Key, Compare, Allocator> & _Right

);

template<class InputIterator>

multiset (

InputIterator _First,

InputIterator _Last

);

template<class InputIterator>

multiset (

InputIterator _First,

InputIterator _Last,

const Compare& _Comp

);

template<class InputIterator>

multiset (

InputIterator _First,

InputIterator _Last,

const Compare& _Comp,

const Allocator& _Al

);

参数：

_Al

The storage allocator class to be used for this set object, which defaults to Allocator.

_Comp

The comparison function of type constTraits used to order the elements in the set, which defaults to Compare.

_Right

The set of which the constructed set is to be a copy.

_First

The position of the first element in the range of elements to be copied.

_Last

The position of the first element beyond the range of elements to be copied.

2.2 迭代函数

const_iterator begin( ) const;

iterator begin( );

功能：

返回指向multiset头部的迭代器

const_iterator end( ) const;

iterator end( );

功能：

返回指向multiset尾部的迭代器

const_reverse_iterator rbegin( ) const;

reverse_iterator rbegin( );

功能：

返回一个指向multiset尾部的逆向迭代器

const_reverse_iterator rend( ) const;

reverse_iterator rend( );

功能：

返回一个指向multiset首尾部的逆向迭代器

2.3.2 擦除数据

iterator erase(

iterator _Where

);

iterator erase(

iterator _First,

iterator _Last

);

size_type erase(

const key_type& _Key

);

参数：

_Where

Position of the element to be removed from the set.

_First

Position of the first element removed from the set.

_Last

Position just beyond the last element removed from the set.

_Key

The key of the elements to be removed from the set.

2.3.3 交换数据

void swap(

set<Key, Traits, Allocator>& _Right

);

参数：

_Right

The argument set providing the elements to be swapped with the target set.

2.3.4 清空数据

void clear( );

2.3 操作函数

const_iterator lower_bound(

const Key& _Key

) const;

iterator lower_bound(

const Key& _Key

);

功能：

返回容器中第一个值大于或等于_Key的元素的iterator位置。

参数：

const Key& _Key, The argument key to be compared with the sort key of an element from the multiset being searched.

const_iterator upper_bound(

const Key& _Key

) const;

iterator upper_bound(

const Key& _Key

);

功能：

返回容器中第一个值大于_Key的元素的iterator位置。

参数：

const Key& _Key, The argument key to be compared with the sort key of an element from the multiset being searched.

pair <const_iterator, const_iterator>

equal_range (

const Key& _Key

) const;

pair <iterator, iterator>

equal_range (

const Key& _Key

);

功能：

返回容器中值等于val的所有元素的范围[beg, end)组成的pair<beg, end> 。即A pair of iterators such that the first is the lower_bound of the key and the second is the upper_bound of the key.

参数：

_Key

The argument key to be compared with the sort key of an element from the multiset being searched.

3、代码范例

#include <iostream>

#include <set>

using namespace std;

void PRINT_ELEMENTS(multiset<int> col1, const char* cstr)

{

multiset<int>::const_iterator pos;

cout << cstr << endl;

for (pos = col1.begin(); pos != col1.end(); ++pos)

{

cout << *pos << " ";

}

}

int main()

{

multiset<int> col1;

col1.insert(2);

col1.insert(5);

col1.insert(4);

col1.insert(6);

col1.insert(1);

col1.insert(5);

PRINT_ELEMENTS(col1, "col1: ");

cout << endl;

multiset<int>::const_iterator pos;

pair<multiset<int>::iterator, multiset<int>::iterator> range;

cout << "lower_bound(3): " << *col1.lower_bound(3) << endl;

cout << "upper_bound(3): " << *col1.upper_bound(3) << endl;

range = col1.equal_range(3);

cout << "equal_range(3): " << *range.first << " " << *range.second << endl;

cout << "elements with value(3): ";

for (pos = range.first; pos != range.second; ++pos)

{

cout << *pos << " ";

}

cout << endl;

cout << endl;

cout << "lower_bound(5): " << *col1.lower_bound(5) << endl;

cout << "upper_bound(5): " << *col1.upper_bound(5) << endl;

range = col1.equal_range(5);

cout << "equal_range(5): " << *range.first << " " << *range.second << endl;

cout << "elements with value(5): ";

for (pos = range.first; pos != range.second; ++pos)

{

cout << *pos << " ";

}

cout << endl;

}

输出：

col1:

1 2 4 5 5 6

lower_bound(3): 4

upper_bound(3): 4

equal_range(3): 4 4

elements with value(3):

lower_bound(5): 5

upper_bound(5): 6

equal_range(5): 5 6

elements with value(5): 5 5