C++ 多重集 clear()

30 Aug 2024 | 3 分钟阅读

C++ 多重集 clear() 函数用于移除多重集容器中的所有元素。它会清空多重集并将其大小变为 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

所有与此容器相关的指针、引用和迭代器都将失效。

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，计算 clear 操作前后多重集的大小

#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

在上面的例子中，一个多重集初始化了 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多重集的元素

#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

在上面的例子中，清空多重集后，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例子来清空多重集的元素

#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.

在上面的例子中，有三组多重集，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;
   
   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

在上面的例子中，一个水果多重集用三种水果初始化。如果输入 0，则水果桶有 4 个元素；如果输入 1，则会清空水果多重集，大小变为 0。

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C++ 多重集 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

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C++ 多重集 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

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