c++ - 为什么打印un_ordered map和map(dictionary)的key和value有异常？

Question

这是我的代码，请告诉我为什么它不从头开始打印，因为在 map 中它是以正确的方式打印

#include<bits/stdc++.h>
using namespace std;

int main(){
unordered_map<int,int>arr;
for(int i=1;i<=10;i++){
    arr[i]=i*i;
}

for(auto it=arr.begin();it!=arr.end();it++){
    cout<<it->first<<" "<<it->second<<"\n";
}

cout<<"normal map \n";

map<int,int>arry;
for(int i=1;i<=10;i++){
    arry[i]=i*i;
}

for(auto it=arry.begin();it!=arry.end();it++){
    cout<<it->first<<" "<<it->second<<"\n";
}

我的输出是

10 100

9 81

8 64

7 49

6 36

5 25

1 1

2 4

3 9

4 16

法线贴图

1 1

2 4

3 9

4 16

5 25

6 36

7 49

8 64

9 81

10 100

为什么 un_ordered map 以这种方式打印值 为什么不像 map 那样打印

Answer 1

std::unordered_map不按任何特定顺序订购 key 。这就是它被称为无序的原因。

Internally, the elements are not sorted in any particular order, but organized into buckets. Which bucket an element is placed into depends entirely on the hash of its key. This allows fast access to individual elements, since once the hash is computed, it refers to the exact bucket the element is placed into.