使用比较运算符将std :: string作为std :: map中的键 [英] std::string as a key in std::map using a compare operator

问题描述

我正在尝试使用std :: string作为std :: map中的键，但是，我无法正确找到().我的代码有些复杂而且很大，所以这是一个小程序，演示了我遇到的问题.如果有人能告诉我为什么这行不通，我将非常感激.

I'm trying to use a std::string as a key in a std::map however, i'm unable to find() correctly. My code is somewhat complicated and large so this is a small program that demonstrates the problem I'm having. If someone could tell me why this doesn't work, i'd be very grateful.

谢谢.

#include <stdio.h>
#include <string>
#include <map>

struct comparer
{
    public:
    bool operator()(const std::string x, const std::string y)
    {
         return x.compare(y)==0;
    }
};

int main(int argc, char *argv[])
{
    std::map<std::string, int, comparer> numbers;
    numbers.insert(std::pair<std::string,int>("One",1));
    numbers.insert(std::pair<std::string,int>("Two",2));
    numbers.insert(std::pair<std::string,int>("Three",3));
    numbers.insert(std::pair<std::string,int>("Four",4));
    numbers.insert(std::pair<std::string,int>("Five",5));


    std::map<std::string, int, comparer>::iterator it=numbers.find("Three");
    if(it!=numbers.end())
        printf("The number is %d\n",(*it).second);
    else
        printf("Error, the number is not found\n");
}

推荐答案

删除您的comparer，它将正常工作.问题是，您没有正确实现它.如果将x放置在之前 y，则应返回true.或将==0更改为<0或>0(这并不重要).

Remove your comparer and it will work just fine. The thing is, you didn't implement it properly. It should return true if x is to be placed before y. Or change ==0 to <0 or >0 (it doesn't really matter).

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