c++ map自定义排序

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在c++中用到map时，如果key是自定义的struct，那么需要自己定义比较函数。因为只有基本类型有默认的比较方法。

typedef struct myKey{int nId;int nVersion;int nNote;}myKey;///自定义map的valuetypedef struct myValue{string strText;}myValue;struct cmp_key{bool operator()(const myKey &k1,const myKey &k2) const{if(k1.nId != k2.nId){return k1.nId < k2.nId;}if(k1.nVersion != k2.nVersion){return k1.nVersion < k2.nVersion;}if(k1.nNote != k2.nNote){return k1.nNote < k2.nNote;}return false;}};int _tmain(int argc, _TCHAR* argv[]){map<myKey,myValue,cmp_key> mymap;myKey k1;k1.nId = 1;k1.nVersion = 2;k1.nNote = 3;myValue v1;v1.strText = "k1: id=1 version=2 note=3";myKey k2;k2.nId = 2;k2.nVersion = 2;k2.nNote = 3;myValue v2;v2.strText = "k1: id=2 version=2 note=3";myKey k3;k3.nId = 2;k3.nVersion = 2;k3.nNote = 5;myValue v3;v3.strText = "k1: id=2 version=2 note=5";mymap[k1] = v1;mymap[k2] = v2;mymap[k3] = v3;for(auto it = mymap.begin(); it != mymap.end(); ++it){cout << it->second.strText.c_str() << endl;}return 0;}

输出:

k1: id=1 version=2 note=3
k1: id=2 version=2 note=3
k1: id=2 version=2 note=5
对value排序的话，用vector<pair>代替。

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