C++ STL中的multiset的clear()函数

multiset::clear() 函数是C++ STL中的内置函数，它从multiset容器中删除所有元素。删除后，multiset容器的最终大小为0。

语法:

multiset_name.clear()

参数: 该函数不接受任何参数。

返回值: 该函数不返回任何内容。

下面的程序阐述了multiset::clear()函数:

程序1:

// C++ program to demonstrate the
// multiset::clear() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
 
    int arr[] = { 15, 10, 15, 11, 10 };
 
    // initializes the set from an array
    multiset<int> s(arr, arr + 5);
 
    // prints all elements in set
    cout << "The elements in multiset are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
 
    cout << "\nThe size after clear() is: ";
 
    // erases all elements
    s.clear();
    cout << s.size();
 
    return 0;
}  

输出:

multiset中的元素为: 10 10 11 15 15
clear()后的大小为: 0

时间复杂度: O(N)

程序2:

// C++ program to demonstrate the
// multiset::clear() function
#include <bits/stdc++.h>
using namespace std;
int main()
{
 
    int arr[] = { 15, 10, 15, 11, 10, 18, 18, 20, 20 };
 
    // initializes the set from an array
    multiset<int> s(arr, arr + 9);
 
    // prints all elements in set
    cout << "The elements in multiset are: ";
    for (auto it = s.begin(); it != s.end(); it++)
        cout << *it << " ";
 
    cout << "\nThe size after clear() is: ";
 
    // erases all elements
    s.clear();
    cout << s.size();
 
    return 0;
}  

输出:

multiset中的元素为: 10 10 11 15 15 18 18 20 20
clear()后的大小为: 0

时间复杂度: O(N)