std::map<int,int>与向量的向量-C/C++实例代码

std::maplt;int, intgt; vs. vector of vector(std::maplt;int,intgt;与向量的向量)

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问题描述

我需要一个容器来根据源 (int) 和目标 (int) 这两个属性存储值 (int)，即当源向目标发送某些内容时，我需要将其作为元素存储在容器中.源由唯一的 int ID(从 0-M 的整数)标识，其中 M 在几十到几百之间，目标 (0-N) 也是如此.容器将通过另一个函数的迭代来更新.

我一直在使用 vector(vector(int))，这意味着按 source(destination(value)) 的顺序进行.后续过程需要检查此容器，以查看特定源和特定目的地的元素是否存在 - 它需要区分空的空间"和填充的空间".容器有可能非常稀疏.

要存储的值可以是 0，所以我没有成功尝试找出空间是否为空，因为我似乎无法执行 container[M][N].empty() 之类的操作.

我没有使用地图的经验，但我看过另一个帖子表明地图可能有用，并且 std::map<int, int> 似乎类似于 vector.

总结一下:

有没有办法检查向量空间"的特定向量是否为空(因为我无法将其与 0 进行比较)
std::map<int, int> 是否更适合此目的，我该如何使用?

解决方案

我需要一个容器来根据两个属性存储一个值(int)，源 (int) 和目标 (int)
std::map
<块引用>
后续进程需要检查这个容器，看看是否有元素存在于一个特定的来源和一个特定的目的地 - 它需要区分一个空的空间"和一个装满的.
std::map::find
http://www.cplusplus.com/reference/map/map/find/
<块引用>容器有可能非常稀疏.

使用 std::map.容器的正确"选择取决于您需要如何查找内容以及需要如何插入/删除内容.如果您想快速找到东西，请使用地图.

I need a container to store a value (int) according to two attributes, source (int) and destination (int) i.e. when a source sends something to a destination, I need to store it as an element in a container. The source is identified by a unique int ID (an integer from 0-M), where M is in the tens to hundreds, and so is the destination (0-N). The container will be updated by iterations of another function.



I have been using a vector(vector(int)) which means goes in the order of source(destination(value)). A subsequent process needs to check this container, to see if an element exists in for a particular source, and a particular destination - it will need to differentiate between an empty 'space' and a filled one. The container has the possibility of being very sparse.

The value to be stored CAN be 0 so I haven't had success trying to find out if the space is empty, since I can't seem to do something like container[M][N].empty(). 

I have no experience with maps, but I have seen another post that suggests a map might be useful, and an std::map<int, int> seems to be similar to a vector<vector<int>>.

To summarise:

Is there a way to check if a specific vector of vector 'space' is empty (since I can't compare it to 0)
Is a std::map<int, int> better for this purpose, and how do I use one?

 解决方案 

  I need a container to store a value (int) according to two attributes,
  source (int) and destination (int)


std::map<std::pair<int, int>, int>



  A subsequent process needs to check this container, to see if an
  element exists in for a particular source, and a particular
  destination - it will need to differentiate between an empty 'space'
  and a filled one.


std::map::find
http://www.cplusplus.com/reference/map/map/find/

  The container has the possibility of being very sparse.
Use a std::map.  The "correct" choice of a container is based on how you need to find things and how you need to insert/delete things.  If you want to find things fast, use a map.

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