unique_ptr用法 - 类的地图 [英] unique_ptr usage - map of class

问题描述

任何人都可以帮助我下面的代码显示类对象的内容？

Can anyone help me with the code below to display the contents of the class object?

Q1 - 任何人都可以确认 - 如果这是在地图中存储指向表类对象的指针的正确方法？

Q1 - can anyone confirm - if this is the correct way to store the pointer to table class object in the map?

Q 2 - 如何输出地图中整个记录的内容？

Q 2 - How to output the contents on the entire record in the map?

感谢

#include <iostream>
#include <map>
#include <memory>
#include <string>

class Table
{
    public:
    int c1, c2, c3;
    Table() {}

    Table(int _c1,int _c2,int _c3)
    {
      c1=_c1;
      c2=_c2;
      c3=_c3;
    }
};

int main()
{

   std::map<int, std::unique_ptr<Table>> mapTable;
   std::unique_ptr<Table> up(new Table(1,2,3));

   // Is this correct way to store the pointer?
   mapTable.insert(std::make_pair(0,std::move(up)));

   // How can I display c1,c2,c3 values here with this iterator?
   for (const auto &i : mapTable)
    std::cout << i.first << " " << std::endl;

   return 0;
}

// How to get the output in the form - 0,1,2,3 ( 0 map key, 1,2,3 are c1,c2,c3 )
// std::cout << i.first << " " << i.second.get() << std::endl;  --> incorrect output

推荐答案

可以任何人确认 - 如果这是正确的方式来存储指向表类对象在地图中？

Q1 - can anyone confirm - if this is the correct way to store the pointer to table class object in the map?

是的，在容器中存储 unique_ptr 的正确方法。唯一指针是不可复制的，所以你需要 std :: move（）时，它传递给一个函数 - 你这样做。

Yes, that is the correct way of storing a unique_ptr in a container. Unique pointers are non-copyable, so you need to std::move() it when passing it to a function - and you are doing that.

Q 2 - 如何输出地图中整个记录的内容？

Q 2 - How to output the contents on the entire record in the map?

除非我缺少一些显而易见的东西，否则你实际上做的最困难的部分。只要执行：

Unless I am missing something obvious, you actually did the hardest part of the job. Just do:

for (const auto &i : mapTable)
{
    std::cout << i.first << " " << std::endl;

    std::cout << i.second->c1 << std::endl;
    std::cout << i.second->c2 << std::endl;
    std::cout << i.second->c3 << std::endl;
}

迭代器是 std :: pair< const int，std :: unique_ptr< Table>> （这是映射的值类型），因此 i.first 访问密钥， i.second 提供对映射值（在您的情况下是唯一指针）的访问。

The iterator is an iterator to a std::pair<const int, std::unique_ptr<Table>> (which is the value type of the map), so i.first provides access to the key, and i.second provides access to the mapped value (the unique pointer, in your case).

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