无论如何，有没有将键，值，值存储到映射中 [英] Is there anyway to store key, value, value into map

问题描述

在阅读了大多数maps问题之后，我最终从此链接中得到了一个主意:

After reading through most of the maps questions, I eventually got an idea from this link: How to unique my data that are stored in an object which are stored in a vector?

我的任务是从用户输入中存储X，Y，Z坐标.为了防止用户输入重复的数据，我决定使用地图容器，因为它们不允许重复的数据.

I have a task of storing X, Y, Z coordinates from the user input. To prevent the user from entering duplicated data, I have decided to use map containers as they do not allow duplicated data.

我测试了代码.

我将X用作key，将Y用作value

我可以通过以下方式存储X和Y:

I am able to store X and Y via this:

map<int, int> mapp2d;
mapp2d.insert(pair<int, int>(X, Y));

并通过以下方式访问它们:

And to access them via this:

map<int, int>::iterator p = mapp2d.begin();
map<int, int>::iterator e = mapp2d.end();
while ( p != mapp2d.end())
{
    cout << "X: " << p->first << " Y: " << p->second << endl;
    p++; 
}

是否可以对X，Y，Z执行此操作?像这样:

Is it possible to do it for X, Y, Z ? Like this:

map<int, int, int> mapp3d
mapp3d.insert(pair<int, int, int>(X, Y, Z))

我测试了代码，但出现了以下错误:

I tested out the code but i got this errors:

error: wrong number of template arguments (3, should be 2)
error: provided for ‘template<class _T1, class _T2> struct std::pair

是的，我确实知道这样做是违法的，但是没有关于该怎么做的教程，而且我的想法已经用光了，我该如何使用它们呢?

Yes, i do know it is illegal for me to do that, but there're no tutorials on how should i do so, and i kind of ran out of ideas, and how can i access them ?

感谢你们的光临，谢谢.

Appreciate you guys for taking a look, thanks in advance.

推荐答案

您应该将坐标存储在一起，而不是将一个坐标用作键:

You should store the coordinates together instead of using one coordinate as key:

struct Point
{
    int x, y, z;

    Point(int x, int y, int z) : x(x), y(y), z(z) {}
};

然后只实现一个自定义比较器:

Then just implement a custom comparator:

struct PointComparator
{
    bool operator()(const Point& a, const Point& b)
    {
        if (a.x < b.x) return true;
        if (a.x == b.x && a.y < b.y) return true;
        if (a.x == b.x && a.y == b.y && a.z < b.z) return true;
        return false;
    }
};

最后，请使用 set 而非地图(因为您的情况是，值和键是相同的):

And finally, use a set instead of a map (because in your case, values and keys are the same):

#include <set>
std::set<Point, PointComparator> points;

---

集合是按顺序排列的(就像地图一样)，默认情况下是从低到高的值.您需要在此处指定一个自定义比较器，因为如果您只是执行std::set<Point>，则使用的默认比较器是std::less.该比较器可以比较数字等，但不知道如何比较类型为Point的对象.因此，该集合无法正确排序其元素，也无法确定两个元素是否相同(这就是您要追求的).如果执行std::set<Point, PointComparator>，则会创建一个使用PointComparator中的逻辑比较其元素的集合.

---

Sets are (just like maps) ordered, by default from low to high values. You need to specify a custom comparator here because the default one that is used if you just do std::set<Point> is std::less. This comparator can compare numbers etc, but has no clue how to compare objects of type Point. The set could therefore not order its elements properly and also not figure out if two elements are identical (which is what you are after). If you do std::set<Point, PointComparator>, you create a set that uses the logic in PointComparator to compare its elements.

此示例将打印"1"和"2":

This example will print "1" and "2":

points.insert(Point(1, 2, 3));
points.insert(Point(1, 2, 3));
points.insert(Point(2, 3, 4));

std::set<Point, PointComparator>::iterator it = points.begin();
while (it != points.end()) {
    std::cout << "x = " << it->x << std::endl;
    it++;
}

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