定制排序集给出“无效运算符” of find（...） [英] Custom ordered set give "invalid operator<" of find(...)

问题描述

在我尝试在自定义有序集中查找元素时遇到问题。

Have a issue when I'm trying to find element in a custom ordered set.

File: c:\program files (x86)\microsoft visual studio 10.0\vc\include\xtree
Line: 1746

Expression: invalid operator<

我需要一组字符串，其中的元素根据我的需要进行排序。

I need a set of strings where the elements are ordered accordingly my needs.

比较器对象：

struct OrderComparator {
public:
    static map<string,int> valueOrder;

    bool operator()( const string lhs, const string rhs ) {
        map<string,int>::iterator resultLhs,resultRhs;
        resultLhs = valueOrder.find(lhs);
        resultRhs = valueOrder.find(rhs);
        if (resultLhs == valueOrder.end() || resultRhs == valueOrder.end())
        {
            return false;
        }
        else {
            bool result = resultLhs->second <= resultRhs->second;
            return result;
        }
    }

    static map<string,int> create_map()
    {
        map<string,int> m;
        m["A"] = 1; 
        m["B"] = 2;
        m["C"] = 3;
        m["D"] = 4;
        return m;
    }
};

---

Comparator工作正常！

---

Comparator is working fine!

但是当我试图在集合中搜索时提到错误。

But when I'm trying to search in the set getting mentioned error.

typedef set<string, OrderComparator> TREESET_CMP;
...
TREESET_CMP::iterator it = myTree.find(obj); <-fails
...

如果有人能告诉我为什么

Will be glad if some one can tell me why this is happening and how to fix it.

完全正常工作Mini示例：

Full working Mini Example:

    #include "stdafx.h"
#include <string>
#include <set>
#include <map>
#include <iterator>
#include <algorithm>
using namespace std;
#include <stdio.h>
#include <tchar.h>

struct OrderComparator {
public:
    static map<string,int> valueOrder;

    bool operator()( const string lhs, const string rhs ) {
        map<string,int>::iterator resultLhs,resultRhs;
        resultLhs = valueOrder.find(lhs);
        resultRhs = valueOrder.find(rhs);
        if (resultLhs == valueOrder.end() || resultRhs == valueOrder.end())
        {
            return false;
        }
        else {
            bool result = resultLhs->second <= resultRhs->second;
            return result;
        }
    }

    static map<string,int> create_map()
    {
        map<string,int> m;
        m["A"] = 1; 
        m["B"] = 2;
        m["C"] = 3;
        m["D"] = 4;
        return m;
    }
};
map<string,int> OrderComparator::valueOrder = OrderComparator::create_map();

typedef set<string, OrderComparator> TREESET_CMP;

int _tmain(int argc, _TCHAR* argv[])
{
    TREESET_CMP myTree;
    myTree.insert("B");
    myTree.insert("C");
    myTree.insert("A");

    TREESET_CMP::const_iterator it = myTree.find("A");
    system("PAUSE");

}

推荐答案

可以是这样：

bool operator()( const string &lhs, const string &rhs ) {
    map<string,int>::iterator resultLhs,resultRhs;
    resultLhs = valueOrder.find(lhs);
    resultRhs = valueOrder.find(rhs);
    if (resultLhs == valueOrder.end()) return false;
    if (resultRhs == valueOrder.end()) return true;

    return resultLhs->second < resultRhs->second;
}

您可以将两行替换为：

if (resultRhs == valueOrder.end()) return false;
if (resultLhs == valueOrder.end()) return true;

如果您希望在地图中不存在的字符串在此之前排序。

If you want strings that do not exist in your map to be sorted before that do.

这篇关于定制排序集给出“无效运算符” of find（...）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！