C++ STL multiset
multiset简介
multiset是 C++ STL的一部分(标准模板库)。多重集是类似于Set的关联容器，用于存储排序后的值(该值本身是T类型的键)，但是与Set仅存储唯一键的Set不同， multiset可以具有重复的键 。默认情况下，它使用运算符比较键。
可以插入或删除multiset中元素的值，但不能更改(元素始终为const)。
语法
template < class T, // multiset::key_type/value_type
class Compare = less<T>, // multiset::key_compare/value_compare
class Alloc = allocator<T> // multiset::allocator_type
> class multiset;
参数
T : 存储在容器多重集中的元素类型。
比较 : 一个比较类，它接受两个具有相同bool类型的参数并返回一个值。此参数是可选的，二进制谓词较少
是默认值。
Alloc : 用于定义存储分配模型的分配器对象的类型。
示例1
让我们看一个演示C++ Multiset的示例:
#include <iostream>
#include <set>
#include <string>
#include <cstdlib>
using namespace std;
int main()
{
multiset<int> ms;
multiset<int>::iterator it, it1, msIt;
int choice, item;
while (1)
{
cout<<"\n---------------------"<<endl;
cout<<"Multiset Example"<<endl;
cout<<"\n---------------------"<<endl;
cout<<"1.Insert Number into the Multiset"<<endl;
cout<<"2.Delete Element from the Multiset"<<endl;
cout<<"3.Find Element in a Multiset"<<endl;
cout<<"4.Count Elements with a specific key"<<endl;
cout<<"5.Size of the Multiset"<<endl;
cout<<"6.Display Multiset"<<endl;
cout<<"7.First Element of the Multiset"<<endl;
cout<<"8.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>choice;
switch(choice)
{
case 1:
cout<<"Enter value to be inserted: ";
cin>>item;
if (ms.empty())
it1 = ms.insert(item);
else
it1 = ms.insert(it1, item);
break;
case 2:
cout<<"Enter value to be deleted: ";
cin>>item;
ms.erase(item);
break;
case 3:
cout<<"Enter element to find ";
cin>>item;
it = ms.find(item);
if (it != ms.end())
cout<<"Element found"<<endl;
else
cout<<"Element not found"<<endl;
break;
case 4:
cout<<"Enter element to be counted: ";
cin>>item;
cout<<item<<" appears "<<ms.count(item)<<" times."<<endl;
break;
case 5:
cout<<"Size of the Multiset: "<<ms.size()<<endl;
break;
case 6:
cout<<"Elements of the Multiset: ";
for (it = ms.begin(); it != ms.end(); it++)
cout<<*it<<" ";
cout<<endl;
break;
case 7:
if(ms.empty())
{
cout<<"Multiset is empty";
}
else
{
msIt = ms.begin();
cout << "The First Element of the Multiset is " << *msIt << endl;
}
break;
case 8:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}
输出:
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 100
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 200
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 1
Enter value to be inserted: 300
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 2
Enter value to be deleted: 200
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 3
Enter element to find 100
Element found
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 4
Enter element to be counted: 100
100 appears 1 times.
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 5
Size of the Multiset: 2
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 6
Elements of the Multiset: 100 300
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 7
The First Element of the Multiset is 100
---------------------
Multiset Example
---------------------
1.Insert Number into the Multiset
2.Delete Element from the Multiset
3.Find Element in a Multiset
4.Count Elements with a specific key
5.Size of the Multiset
6.Display Multiset
7.First Element of the Multiset
8.Exit
Enter your Choice: 8
示例2
让我们看另一个示例来演示C++ Multiset:
#include <iostream>
#include <set>
#include <iterator>
using namespace std;
int main()
{
// empty multiset container
multiset <int, greater <int> > ms1;
// insert elements in random order
ms1.insert(400);
ms1.insert(300);
ms1.insert(600);
ms1.insert(200);
ms1.insert(500);
ms1.insert(500); // 500 will be added again to the multiset unlike set
ms1.insert(100);
// printing multiset ms1
multiset <int> :: iterator itr;
cout << "\nMarks of ms1 class Room: "<<endl;
for (itr = ms1.begin(); itr != ms1.end(); ++itr)
{
cout << " " << *itr;
}
cout << endl;
// assigning the elements from ms1 to ms2
multiset <int> ms2(ms1.begin(), ms1.end());
// print all elements of the multiset ms2
cout << "\nThe Number of students in class Room after assigning class Room students: "<<endl;
for (itr = ms2.begin(); itr != ms2.end(); ++itr)
{
cout << " " << *itr;
}
cout << endl;
// Find the highest element in multiset ms1 and ms2
multiset<int>::iterator msIt1, msIt2;
msIt1 = ms1.begin();
cout<< "\nHighest marks in ms1 class Room: "<<*msIt1;
msIt2 = ms2.begin();
cout<< "\nHighest marks in ms2 class Room: "<<*msIt2;
// remove all elements up to element with value 300 in ms2
cout << "\n\nms2 class Room after removal of Students less than 300 marks:\n ";
ms2.erase(ms2.begin(), ms2.find(300));
for (itr = ms2.begin(); itr != ms2.end(); ++itr)
{
cout << " " << *itr;
}
// remove all elements with value 500 in ms2
int num;
num = ms2.erase(500);
cout << "\n\nms2.erase(500) : ";
cout << num << " removed \t" ;
for (itr = ms2.begin(); itr != ms2.end(); ++itr)
{
cout << " " << *itr;
}
cout << endl<<endl;
//lower bound and upper bound for multiset ms1
cout << "ms1.lower_bound(400) : " << *ms1.lower_bound(400) << endl;
cout << "ms1.upper_bound(400) : " << *ms1.upper_bound(400) << endl;
//lower bound and upper bound for multiset ms2
cout << "ms2.lower_bound(400) : " << *ms2.lower_bound(400) << endl;
cout << "ms2.upper_bound(400) : " << *ms2.upper_bound(400) << endl;
return 0;
}
输出:
Marks of ms1 class Room:
600 500 500 400 300 200 100
The Number of students in class Room after assigning class Room students:
100 200 300 400 500 500 600
Highest marks in ms1 class Room: 600
Highest marks in ms2 class Room: 100
ms2 class Room after removal of Students less than 300 marks:
300 400 500 500 600
ms2.erase(500) : 2 removed 300 400 600
ms1.lower_bound(400) : 400
ms1.upper_bound(400) : 300
ms2.lower_bound(400) : 400
ms2.upper_bound(400) : 600
成员函数
以下是multiset的所有成员函数的列表:
构造函数/析构函数
迭代器
容量
修饰符
观察者
操作
分配器
非成员重载函数
