C++ set clear()

30 Aug 2024 | 3 分钟阅读

C++ set clear() 函数用于移除集合容器中的所有元素。它会清空集合并将其大小变为 0。

语法

void clear();                 //until C++ 11
void clear() noexcept;      //since C++ 11

参数

无

返回值

无

复杂度

大小呈线性。

迭代器有效性

与此容器相关的所有迭代器、引用和指针都将失效。

数据竞争

容器被修改。

所有包含的元素都将被修改。

异常安全

此函数从不抛出异常。

示例 1

让我们看一个简单的例子来计算 clear 操作前后集合的大小

#include <iostream>
#include <set>
using namespace std;

int main() {

   set<int> myset = {10,20,30,40}; 

   cout << "Initial size of set before clear operation = " << myset.size() << endl;

   myset.clear();

   cout << "Size of set after clear operation = " << myset.size() << endl;

   return 0;
}

输出

Initial size of set before clear operation = 4
Size of set after clear operation = 0

在上面的例子中，一个集合初始化时有 4 个元素，因此大小为 4，但在 clear 操作后，大小变为 0。

示例 2

让我们看一个简单的例子来清空集合的元素

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  set<string> myset;

  myset = {"Nikita","Deep","Aman"};

  cout << "myset contains:\n";
  for (set<string>::iterator it=myset.begin(); it!=myset.end(); ++it)
    cout << *it<< '\n';

  myset.clear();
  
  myset= {"Divya", "Raaz"};

  cout << "\nmyset contains:\n";
  for (set<string>::iterator it=myset.begin(); it!=myset.end(); ++it)
    cout << *it<< '\n';

  return 0;
}

输出

myset contains:
Aman
Deep
Nikita

myset contains:
Divya
Raaz

在上面的例子中，清空集合后，我们可以添加新元素而无需重新初始化。

示例 3

让我们看一个简单的例子来清空集合的元素

#include <iostream>
#include <set>

using namespace std;

int main ()
{
  int n;
  set<string> m1,m2,m3;
  
  m1 = {"Hello", "World"};
  m2 = {"Java", "Program"};
  m3 = {"C++", "Coding"};

  cout << "m1 group has following members:\n";
  for (set<string>::iterator it=m1.begin(); it!=m1.end(); ++it)
    cout << *it << ' ';
  

  cout << "\n\nm2 group has following members:\n";
  for (set<string>::iterator it=m2.begin(); it!=m2.end(); ++it)
    cout << *it<< ' ';

  cout << "\n\nm3 group has following members:\n";
  for (set<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.

在上面的例子中，有三组集合，根据用户的选择，其中一组已被删除。

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;
   
   set<string> fruit = {"Banana","Apple","Orange"};

   cout << "Fruit bucket has following fruits = \n";
   for (set<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
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 
Orange

Do you want to clear your fruit bucket?
Press 1 for Yes and 0 for No: 1
3 fruits in bucket

在上面的例子中，一个水果集合初始化时包含三种水果。询问是否清空集合，如果你输入 0，则水果桶中有 3 个元素；如果你输入 1，则会清空水果集合，大小变为 0。

下一主题Set emplace() 函数

C++ set clear()

语法

参数

返回值

复杂度

迭代器有效性

数据竞争

异常安全

示例 1

示例 2

示例 3

示例 4

联系信息

关注我们

教程

面试题

在线编译器

Python

Java

.Net Framework

AI, ML and Data Science

Cloud Technology

B.Tech and MCA

Web Technology

PHP

Software Testing

Technical Interview

Java Interview

Python

Web Interview

Database Interview

B.Tech / MCA

Important Interview

Software Testing Interview

Company Interviews

Online Compilers

Multiple Choice Questions

C++ 教程

C++ 控制语句

C++ 函数

C++ 数组

C++ 类和对象

C++ 构造函数

C++ 继承

C++ 多态

C++ 抽象

C++ 命名空间

C++ 模板

C++ 字符串

C++ 指针

信号处理

C++ 异常

C++ 文件与流

C++ STL 教程

面试题

选择题

C++ 程序

C++ STL Stack

C++ STL Bitset

C++ STL Deque

C++ STL List

C++ STL Map

C++ STL Math

C++ STL priority_queue

C++ STL Queue

C++ STL Multiset

C++ STL Multimap

C++ STL Set

C++ STD Strings

C++ STL Vector

C++ 操纵符

C++ STL Algorithms

C++ Algorithm

C++ Iterators

C++ 杂项

C++ set clear()

语法

参数

返回值

复杂度

迭代器有效性

数据竞争

异常安全

示例 1

示例 2

示例 3

示例 4

相关帖子

set get_allocator() 函数

set equal_range() 函数

set end() 函数

set count() 函数

set value_comp() 函数

set 析构函数

set begin() 函数

set 构造函数

set rend() 函数