• map正序、逆序排序


    一、按 key 排序

      1.map顺序排序(小的在前,大的在后)

      map<float,string,less<float> > m_aSort;//float从小到大排序

      2.map逆序排序(大的在前,小的在后)

      map<float,string,greater<float> > m_aSortR;//float从大到小排序

       

      注:  

       用 greater_equal(less_equal) 做第三个参数来排序,map的 find 函数会失败。

       如果需要存储相同key值的 键值对,可以用multimap,参见:https://www.cnblogs.com/SZxiaochun/p/10482964.html

    struct SIndexData
    {
    	string sCode;
    	int iDate;
    	int iTime;
    	float f1;
    	SIndexData():
    	iDate(0),
    	iTime(0)
    	{
    	}
    
    	bool operator == (const SIndexData & obj) const
    	{
    		return sCode == obj.sCode && iDate == obj.iDate && iTime == obj.iTime;
    	}
    
    	bool operator < (const SIndexData & obj) const
    	{
    		return iDate < obj.iDate ;
    	}
    };
    
    map<float, SIndexData, greater_equal<float> > m_is;
    
    SIndexData sIndexData1;
    sIndexData1.sCode = "000001";
    sIndexData1.iDate = 20171025;
    sIndexData1.iTime = 94000;
    sIndexData1.f1 = 7.8f;
    m_is[sIndexData1.f1] = sIndexData1;
    
    SIndexData sIndexData2;
    sIndexData2.sCode = "000002";
    sIndexData2.iDate = 20171025;
    sIndexData2.iTime = 94000;
    sIndexData2.f1 = 7.9f;
    m_is[sIndexData2.f1] = sIndexData2;
    
    SIndexData sIndexData3;
    sIndexData3.sCode = "000004";
    sIndexData3.iDate = 20171025;
    sIndexData3.iTime = 94000;
    sIndexData3.f1 = 7.8f;
    //m_is[sIndexData3.f1] = sIndexData3;
    m_is.insert(make_pair(sIndexData3.f1, sIndexData3));
    
    SIndexData sIndexData4 = m_is[sIndexData3.f1];
    
    map<float, SIndexData, greater_equal<float> >::iterator iter = m_is.find(sIndexData3.f1);
    if (iter != m_is.end())
    {
    	cout << "find succ" << endl;
    }
    else
    {
    	cout << "find error" << endl;
    }
    
    getchar();

    原因分析参见:https://www.cnblogs.com/Harley-Quinn/p/7247978.html

    二、按 value 排序

    typedef pair<int, string> PAIR;
    
    bool CmpByValue(const PAIR & lhs, const PAIR & rhs)
    {
    	return lhs.second < rhs.second;    //按 value 从小到大排序。如果 value 不是基础类型(int、short等),而是自己定义的结构体,就在结构体中重载 < 运算符(详见:http://www.cnblogs.com/SZxiaochun/p/6377084.html 第41行)。
    }
    
    map<int,string> m_two;
    
    m_two[1] = "xiaochun";
    m_two.insert(make_pair(2,"chunxiao"));
    	
    vector<PAIR> vPair;
    vPair.insert(vPair.end(), m_two.begin(), m_two.end());
    
    sort(vPair.begin(), vPair.end(), CmpByValue);
    

      

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  • 原文地址:https://www.cnblogs.com/SZxiaochun/p/6377097.html
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