在C ++中使用.find()和struct作为键 [英] Using .find() with struct as key in map in C++

问题描述

我无权使用BOOST或STL；我的结构和映射类似于以下伪指令:

I do not have access to BOOST or STL; my struct and map looks similar to the following psuedo:

 struct s_map_key{
    int a;
    int b;
    bool operator<(const s_map_key& smk) const 
    {
        if (a < smk.a)       
        {            
            return true;
        } else if (a == smk.a)  
        { 
            if (b < smk.b) 
            { 
                return true;
            } 
            else if (b == smk.b)
            {
                return true;
            }
        } 
            return false;
    }
};

int main(int argc, char* argv[])
{

    std::multimap<s_map_key, std::string> myMap;
    for(int i = 0; i <10; i++)
    {
    s_map_key smk;
    smk.a = i;
    smk.b = 2;
    myMap.insert(std::make_pair(smk, "test"));
    }

    s_map_key smk;
    smk.a = 3;
    std::multimap<s_map_key, std::string>::iterator x = myMap.find(smk);
    if(x != myMap.end())
    {
        std::cout << x->first.a <<std::endl;
        std::cout << x->first.b <<std::endl;
    }
    return 0;
}

我想做的是在我的多重地图中搜索A = 2，B = 2或A&的所有情况. B =2.我不确定，但是，我认为我需要在我的结构中创建谓词以查找".想法?

What I am trying to do is search my multimap for all cases where A = 2, B = 2, or A & B = 2. I am not exactly sure but, I think i need to create the predicates in my struct for "finding". Ideas?

推荐答案

operator<是find或其他所有功能的全部.但是，您的实现有一个错误.如果操作数相等，则返回true.

operator< is all you need for find or anything else. However, your implementation has a bug. It returns true if the operands are equal.

find和其他标准库组件使用a == b iff ! (a < b) && ! (b < a)的假设，因此，如果a和b相等，则<必须为false才能使find正常工作.

find and other Standard Library components use the assumption that a == b iff ! (a < b) && ! (b < a), so if a and b are equal, < must be false for find to work.

        else if (b == smk.b)
        {
            return false; // was true
        }

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