C++ multiset clear()
C++ multiset clear()
C++ multiset 合 clear()函数用于删除 multiset 合容器的所有元素。清除 multiset 并将其大小转换为0。
语法
void clear(); //until C++ 11
void clear() noexcept; //since C++ 11
参数
无
返回值
无
复杂度
线性大小。
迭代器有效性
与此容器相关的所有指针,引用和迭代器均无效。
数据竞争
容器已修改。
所有包含的元素均已修改。
异常安全性
此函数永远不会引发异常。
示例1
让我们看一个简单的示例,在清除操作之前和之后计算 multiset 的大小:
#include <iostream>
#include <set>
using namespace std;
int main() {
multiset<int> mymultiset = {10,20,20,30};
cout << "Initial size of multiset before clear operation = " << mymultiset.size() << endl;
mymultiset.clear();
cout << "Size of multiset after clear operation = " << mymultiset.size() << endl;
return 0;
}
输出:
Initial size of multiset before clear operation = 4
Size of multiset after clear operation = 0
在上面的示例中,使用4个元素初始化了一个 multiset ,因此大小为4,但是在清除操作之后,大小变为0。
示例2
让我们看一个简单的示例来清除 multiset 的元素:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
multiset<string> mymultiset;
mymultiset = {"Nikita","Deep","Aman"};
cout << "mymultiset contains:\n";
for (multiset<string>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
cout << *it<< '\n';
mymultiset.clear();
mymultiset= {"Deep", "Raaz"};
cout << "\nmymultiset contains:\n";
for (multiset<string>::iterator it=mymultiset.begin(); it!=mymultiset.end(); ++it)
cout << *it<< '\n';
return 0;
}
输出:
mymultiset contains:
Aman
Deep
Nikita
mymultiset contains:
Deep
Raaz
在上面的示例中,清除了 multiset 后,我们可以添加新元素而无需初始化。
示例3
让我们看一个简单的示例清除 multiset 的元素:
#include <iostream>
#include <set>
using namespace std;
int main ()
{
int n;
multiset<string> m1,m2,m3;
m1 = {"Hello", "World"};
m2 = {"Java", "Program"};
m3 = {"C++", "Coding"};
cout << "m1 group has following members:\n";
for (multiset<string>::iterator it=m1.begin(); it!=m1.end(); ++it)
cout << *it << ' ';
cout << "\n\nm2 group has following members:\n";
for (multiset<string>::iterator it=m2.begin(); it!=m2.end(); ++it)
cout << *it<< ' ';
cout << "\n\nm3 group has following members:\n";
for (multiset<string>::iterator it=m3.begin(); it!=m3.end(); ++it)
cout << *it<< ' ';
cout<<"\n\nWhich group do you want to delete?\n 1.m1\n 2.m2\n 3.m3\n Please enter your choice: ";
cin>>n;
if(n==1){
m1.clear();
cout<<"\nGroup m1 has been cleared.";
}
else if(n==2){
m2.clear();
cout<<"\nGroup m2 has been cleared.";
}
else if(n==3){
m3.clear();
cout<<"\nGroup m3 has been cleared.";
}
else
cout<<"Invalid option!";
return 0;
}
输出:
m1 group has following members:
Hello World
m2 group has following members:
Java Program
m3 group has following members:
C++ Coding
Which group do you want to delete?
1.m1
2.m2
3.m3
Please enter your choice: 2
Group m2 has been cleared.
在上面的示例中,有3组 multiset ,并且根据用户的选择删除了一组。
示例4
让我们看一个简单的例子:
#include <iostream>
#include <set>
using namespace std;
int main() {
int n;
multiset<string> fruit = {"Banana","Apple","Orange","Banana"};
cout << "Fruit bucket has following fruits = \n";
for (multiset<string>::iterator it=fruit.begin(); it!=fruit.end(); ++it)
cout << *it<< '\n';
cout<<"\ndo you want to clear your fruit bucket?\nPress 1 for Yes and 0 for No: ";
cin>>n;
if( n==1){
fruit.clear();
cout<<fruit.size()<<" fruits in bucket \n";
}
else if(n==0)
cout <<fruit.size() << " fruits in bucket \n" ;
return 0;
}
输出:
1.
Fruit bucket has following fruits =
Apple
Banana
Banana
Orange
do you want to clear your fruit bucket?
Press 1 for Yes and 0 for No: 1
0 fruits in bucket
2.
Fruit bucket has following fruits =
Apple
Banana
Banana
Orange
do you want to clear your fruit bucket?
Press 1 for Yes and 0 for No: 1
4 fruits in bucket
在上面的示例中,一个水果 multiset 用三个水果初始化。要求清除 multiset ,如果输入0,则水果桶有4个元素;如果输入1,则清除水果 multiset ,大小变为0。