unordered_map 具有三个元素 [英] unordered_map to have three elements
问题描述
我试图在 unordered_map
中包含三个元素.我尝试了以下代码
I am trying to have three elements in an unordered_map
. I tried the following code
#include <iostream>
#include <string>
#include <algorithm>
#include <boost/unordered_map.hpp>
typedef boost::unordered_map<int, std::pair<int, int>> mymap;
mymap m;
int main(){
//std::unordered_map<int, std::pair<int, int> > m;
m.insert({3, std::make_pair(1,1)});
m.insert({4, std::make_pair(5,1)});
for (auto& x: m)
std::cout << x.first << ": "<< x.second << std::endl;
}
但是我在打印语句中遇到很多错误,比如
but I get many errors in the print statement something like
‘std::pair’不是从‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’派生的std::cout <<x.第一个<<": "<
‘std::pair’ is not derived from ‘const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’ std::cout << x.first << ": "<< x.second << std::endl;
推荐答案
打印语句中的问题.应该是这样的:
The problem in your printing statement. It should be like this:
std::cout << x.first << ": "<< x.second.first << ","<< x.second.second << std::endl;
_______________________________^^^^^^^^^^^^^^__________^^^^^^^^^^^^^^^_______________
你不能直接打印std::pair
.您需要单独打印每个项目.
You can not just print std::pair
directly. You need to print each item separately.
没有ostream&
重载,但 std::pair
的运算符<<int
有一个重载.
There is no ostream& operator<<
overload for std::pair
but there is one for int
.
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