C++ set clear()函数

C++ set clear() 函数用于从集合容器中移除所有元素。它清空集合并将其大小转换为0。

语法

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

参数

无

返回值

无

复杂度

与大小成正比

迭代器有效性

该容器相关的所有迭代器、引用和指针都会失效

数据竞争

容器被修改

所有包含的元素都被修改

异常安全性

此函数不会抛出异常

示例1

让我们来看一个简单的示例，在清除操作之前和之后计算集合的大小：

#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

在上面的示例中，一个集合被初始化为4个元素，因此大小为4，但是经过清除操作后，大小变为0。

示例2

让我们看一个清除集合元素的简单示例：

#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

在上面的示例中，清空集合后，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来清楚集合的元素：

#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.

在上面的示例中，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示例：

#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

在以上示例中，一个水果集合被初始化为三个水果。如果输入0，则清空水果桶并包含3个元素；如果输入1，则清空水果集合，并且大小变为0。