遍历无序映射 C++
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Iterate through unordered map C++
提问by Yoda
I have wrote program which reads input until you hit ',' - COMA at the input. Then it counts the number of letters you put in,
我已经编写了读取输入的程序，直到您在输入处点击 ',' - COMA。然后它会计算你输入的字母数，
I want to iterate through this map but it says that itcannot be defined wih no type:
我想遍历这个地图，但它说it不能在没有类型的情况下定义：
#include <iostream>
#include <conio.h>
#include <ctype.h>
#include <iostream>
#include <string>
#include <tr1/unordered_map>
using namespace std;
int main(){
cout<<"Type '.' when finished typing keys: "<<endl;
char ch;
int n = 128;
std::tr1::unordered_map <char, int> map;
do{
ch = _getch();
cout<<ch;
if(ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z'){
map[ch] = map[ch] + 1;
}
} while( ch != '.' );
cout<<endl;
for ( auto it = map.begin(); it != map.end(); ++it ) //ERROR HERE
std::cout << " " << it->first << ":" << it->second;
return 0;
}
回答by Basile Starynkevitch
You are using autoso you have C++11code. You need a C++11 compliant compiler (e.g. GCC 4.8.2 or newer).
As Peter G.commented, don't name your variable map(which is std::map) but e.g. mymapSo please
您正在使用，auto所以您拥有C++11代码。您需要一个符合 C++11 的编译器（例如 GCC 4.8.2 或更新版本）。正如Peter G.评论的那样，不要命名您的变量map（即std::map），而是例如mymap所以请
#include <unordered_map>
(no need for tr1!)
（不需要tr1！）
Then compile with g++ -std=c++11 -Wall -g yoursource.cc -o yourprogand code a range based for loop
然后使用基于范围的 for 循环进行编译g++ -std=c++11 -Wall -g yoursource.cc -o yourprog和编码
for (auto it : mymap)
std::cout << " " << it.first << ":" << it.second << std::endl;
回答by Dorin Laz?r
With C++17 you can use a shorter, smarter version, like in the code below:
使用 C++17，您可以使用更短、更智能的版本，如下面的代码所示：
unordered_map<string, string> map;
map["hello"] = "world";
map["black"] = "mesa";
map["umbrella"] = "corporation";
for (const auto & [ key, value ] : map) {
cout << key << ": " << value << endl;
}
回答by Walter
Add -std=c++11to your compiler flags (with gcc/icc/clang) if you want to use auto(and other C++11 features). Btw, unordered_mapis in stdin C++11 ... Also there is std::isalpha...
-std=c++11如果您想使用auto（和其他 C++11 功能），请添加到您的编译器标志（使用 gcc/icc/clang ）。顺便说一句，unordered_map是std在C ++ 11 ...也有std::isalpha...
回答by Erik Campobadal
Based on Dorin Laz?r answer, another possible solution is:
基于 Dorin Laz?r 的回答，另一种可能的解决方案是：
unordered_map<string, string> my_map;
my_map["asd"] = "123";
my_map["asdasd"] = "123123";
my_map["aaa"] = "bbb";
for (const auto &element : my_map) {
cout << element.first << ": " << element.second << endl;
}
