map重写比较器

结构体作为map的key或放入set中,需要重载<运算符,如下:

typedef struct tagRoadKey
{
    int m_i32Type;
    int m_i32Scale;

    bool operator <(const tagRoadKey& other) const // 注意是const函数!!
    {
        if (m_i32Type != other.m_i32Type) // 类型按升序排序
        {
            return (m_i32Type < other.m_i32Type);
        }
        else // 如果类型相同,按比例尺升序排序
        {
            return (m_i32Scale < other.m_i32Scale);
        }
    }

} RoadKey;

也可以重载>运算符,示例如下:

#include <iostream>
#include <string>
#include <map>

using namespace std;

class Array
{
private:
    int m_i32Num1;
    int m_i32Num2;

public:
    Array(int i32Num1, int i32Num2);
    bool operator >(const Array& other) const;
};

Array::Array(int i32Num1, int i32Num2)
{
    m_i32Num1 = i32Num1;
    m_i32Num2 = i32Num2;
}

bool Array::operator >(const Array& other) const
{
    if (m_i32Num1 > other.m_i32Num1)
    {
        return true;
    }
    else
    {
        return false;
    }
}

// 此结构体作为map的value
struct TInfo
{
    int m_i32Num1;
    int m_i32Num2;
};

int main(int argc, char* argv[])
{
    map<Array, TInfo, greater<Array> > stMap;

    TInfo stInfo1 = { 1, 1};
    stMap.insert(pair<Array, TInfo>(Array(1, 2), stInfo1));

    TInfo stInfo2 = { 2, 1, 1 };
    stMap.insert(pair<Array, TInfo>(Array(2, 2), stInfo2));

    TInfo stInfo3 = { 3, 1, 1 };
    stMap.insert(pair<Array, TInfo>(Array(3, 2), stInfo3));

    for (map<Array, TInfo, greater<Array> >::iterator it = stMap.begin(); it != stMap.end(); ++it)
    {
        cout << it->second.m_i32Num1 << endl;
    }

    return 0;
}
说明:
 map缺省是用less<Key>作为比较器,所以它要求作为Key的类要重载“<”操作符,没有重载“<”操作符,而是重载了“>”操作符就会报错。
反之,也可以显式地用greater<Key>作为比较器,此时就必要重载Key类中的“>”操作符了。
附:stl中map和set的声明,二者比较像,底层都是用红黑树实现的

template < class Key, class Compare = less<Key>,
           class Allocator = allocator<Key> > class set;

template < class Key, class T, class Compare = less<Key>,
           class Allocator = allocator<pair<const Key,T> > > class map;
 
template < class Key, class Compare = less<Key>,
           class Allocator = allocator<Key> > class multiset;
 
template < class Key, class T, class Compare = less<Key>,
           class Allocator = allocator<pair<const Key,T> > > class multimap;
 
从上面的声明可以看出,也可以定义一个函数对象Compare,声明map或set类型时传进入,如:

struct TTimeCompare
{
    bool operator ()(const CTimerEvent* po1, const CTimerEvent* po2)const
    {        
        return (po1->m_oNextTick < po2->m_oNextTick);
    }
};

typedef multiset<CTimerEvent*, TTimeCompare> TEventSet;


struct ltstr // less than
{
    bool operator()(const char* s1, const char* s2) const
    {
        return strcmp(s1, s2) < 0;
    }
};




set<const char*, ltstr> stSet; // set<Key, Compare, Alloc>
map<const char*, int, ltstr> stMap; // map<Key, Data, Compare, Alloc>




struct eqstr // equal
{
    bool operator()(const char* s1, const char* s2) const
    {
        return strcmp(s1, s2) == 0;
    }
};


hash_map<const char*, int, hash<const char*>, eqstr> stHashMap;  // hash_map<Key, Data, HashFcn, EqualKey, Alloc>


// 自定义hash函数
namespace std
{
    template<>
    struct hash<KEY_TYPE>
    {
        size_t operator()(const KEY_TYPE& key) const
        {
            //return key.Hash();
        }
    };
}

 相等的时候返回false,否则报错

posted @ 2014-04-21 10:22  zzyoucan  阅读(2873)  评论(0编辑  收藏  举报