如何在C++中从地图中删除最后一个元素

如果我们希望从地图中删除最后一个元素，可以使用以下方法：

1. 使用prev(mp.end()) ：prev函数的作用是，它从给定的迭代器后退了一步。因此，将prev函数与mp.end()结合使用将返回一个迭代器，该迭代器指向地图的最后一个元素。
   执行：

   #include 
     
   using namespace std;
     
   int main()
   {
     
       map mp;
     
       // Adding some elements in mp
       mp[1] = 10;
       mp[2] = 20;
       mp[3] = 30;
     
       cout << "Contents of mp before deleting"
              " the last element :\n";
       for (auto it = mp.begin(); it != mp.end(); it++)
           cout << it->first << " ==> "
                << it->second << "\n";
     
       cout << "Deleting the last element from"
              " the map.\n";
       mp.erase(prev(mp.end()));
     
       cout << "Contents of mp after deleting the last"
               " element :\n";
       for (auto it = mp.begin(); it != mp.end(); it++)
           cout << it->first << " ==> "
                << it->second << "\n";
   }
   

   输出：

   Contents of mp before deleting the last element :
   1 ==> 10
   2 ==> 20
   3 ==> 30
   Deleting the last element from the map.
   Contents of mp after deleting the last element :
   1 ==> 10
   2 ==> 20
   

2. using iterator– ：将迭代器设置为mp.end()，然后使用iterator–到达映射中的最后一个元素，然后使用擦除函数将其删除。
   执行：

   #include 
     
   using namespace std;
     
   int main()
   {
     
       map mp;
       // Adding some elements in mp
       mp[1] = 10;
       mp[2] = 20;
       mp[3] = 30;
     
       cout << "Contents of mp before deleting "
               "the last element :\n";
       for (auto it = mp.begin(); it != mp.end(); it++)
           cout << it->first << " ==> " 
                << it->second << "\n";
     
       cout << "Deleting the last element from"
               " the map.\n";
       auto it = mp.end();
       it--;
       mp.erase(it);
     
       cout << "Contents of mp after deleting the"
               " last element :\n";
       for (auto it = mp.begin(); it != mp.end(); it++)
           cout << it->first << " ==> "
                << it->second << "\n";
   }
   

   输出：

   Contents of mp before deleting the last element :
   1 ==> 10
   2 ==> 20
   3 ==> 30
   Deleting the last element from the map.
   Contents of mp after deleting the last element :
   1 ==> 10
   2 ==> 20
   

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