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C++ Multimap 中的 erase函数

C++multimap erase()函数用于从multimap集合中删除与给定键值关联的单个元素或一系列元素。因此，将通过删除元素的数量来减小尺寸。

erase - 语法

void erase (iterator position);                       	  //until C++ 11
size_type erase (const key_type& k);    		  //until C++ 11
void erase (iterator first, iterator last);  		  //until C++ 11
iterator  erase (const_iterator position);		  //since C++ 11
size_type erase (const key_type& k);		  //since C++ 11	
iterator  erase (const_iterator first, const_iterator last); //since C++ 11

erase - 参数

position - 迭代器，指向要从multimap中删除的单个元素。

k - 要从多重映射中删除的元素的键。

first - 要擦除的参数的开始。

last - 要擦除的参数的结尾。

erase - 返回值

它返回一个指向已删除元素的下一个元素的迭代器，或者返回已删除元素的数量。erase - 例子1

让我们看一个简单的示例，该示例通过迭代器擦除元素。

复制代码

#include <iostream>
#include <map>

using namespace std;

int main ()
{
  multimap<char,int> mymultimap;
  multimap<char,int>::iterator it;


  mymultimap= {
              {'a', 100},
              {'b', 200},
              {'b', 300},
              {'c', 400}
              };
  
  cout<<"Before erasing the element: \n";
   for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';

  it=mymultimap.find('b');
  mymultimap.erase (it);                  //erasing by iterator

  cout<<"\nAfter erasing the element: \n";
  for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';
  return 0;
}

输出:

Before erasing the element: 
a => 100
b => 200
b => 300
c => 400

After erasing the element: 
a => 100
b => 300
c => 400

在上面的示例中，元素被迭代器擦除。

erase - 例子2

让我们看一个简单的示例，用给定的键值擦除multimap的元素:

复制代码

#include <iostream>
#include <map>

using namespace std;

int main ()
{
  multimap<char,int> mymultimap;
  multimap<char,int>::iterator it;

  mymultimap = {
               {'a', 100},
               {'b', 200},
               {'b', 300},
               {'c', 400}
               };
  
  cout<<"Before erasing the element: \n";
   for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';

 mymultimap.erase ('b');                 //erasing by key

  cout<<"\nAfter erasing the element: \n";
  for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
    std::cout << it->first << " => " << it->second << '\n';
  return 0;
}

输出:

Before erasing the element: 
a => 100
b => 200
b => 300
c => 400

After erasing the element: 
a => 100
c => 400

在上面的示例中，delete(key)函数从多重映射中删除所有键" b"及其值。

erase - 例子3

让我们看一个简单的示例，以给定参数擦除元素:

复制代码

#include <iostream>
#include <map>

using namespace std;

int main ()
{
  multimap<char,int> mymultimap;
  multimap<char,int>::iterator it;

  mymultimap = {
               {'a', 100},
               {'b', 200},
               {'b', 300},
               {'c', 400}
               };
  
  cout<<"Before erasing the element are: \n";
   cout<<"Size is: "<<mymultimap.size()<<'\n';

   for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
   cout << it->first << " => " << it->second << '\n';

   mymultimap.erase ( mymultimap.begin () ,  mymultimap.end () );  //erasing by range

  cout<<"\nAfter erasing the element are: \n";
  cout<<"Size is: "<<mymultimap.size();

  for (it=mymultimap.begin(); it!=mymultimap.end(); ++it)
  cout << it->first << " => " << it->second << '\n';
  return 0;
}

输出:

Before erasing the element are: 
Size is: 4
a => 100
b => 200
b => 300
c => 400

After erasing the element are: 
Size is: 0

erase - 例子4

让我们看一个简单的示例，从多重映射中删除所有奇数:

链接：https://www.learnfk.comhttps://www.learnfk.com/c++/cpp-multimap-erase-function.html

来源：LearnFk无涯教程网

在线运行复制代码

#include <map>
#include <iostream>

using namespace std;

int main()
{
    multimap<int, string> m = { {1, "one"}, 
                                {2, "two"}, 
                                {3, "three"},
                                {4, "four"}, 
                                {5, "five"}, 
                                {6, "six"}
                               };
                          
   //erase all odd numbers from m
    cout<<"After erasing odd numbers,elements are:\n ";
    for(auto it = m.begin(); it != m.end(); )
        if(it->first % 2 == 1)
            it = m.erase(it);
        else
            ++it;
    for(auto& p : m)
        cout <<p.first <<", "<< p.second << "\n ";
}

输出:

After erasing odd numbers, elements are:
 2, two
 4, four
 6, six

在上面的示例中，所有奇数均已删除，并显示偶数。

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