maps和multimaps

1、对于<set><multiset><map>和<multimap>如果准则不同，准则本身也会被赋值（assigned）或交换(swapped)。

2、在<map><multimap>中，所有的元素的key都被视为常数。元素的实质型别是pair<const key ,T >(确保不会因为变更元素的value而破坏已排好的元素次序)。

注：如果你一定要改变元素的key，只有一条路：以一个"value相同"的新元素替换旧元素。（即删除旧元素，插入一个新元素，只是旧和新元素的value值相同。）

map提供一个种简便方法：

//insert new element with value of old elementcoll["new_key"] = coll["old_key"];//remove old elementcoll.erase("old_key");

3.移除"拥有某个value(而非某个key)"的元素的代码如下(P205)：

typedef std::map<std::string,float> StringFloatMap;StringFloatMap coll;StringFloatMap::iterator pos;...// remove all elements having a certain valuefor(pos = coll.begin(); pos != coll.end();){if(pos->second == value) {coll.erase(pos++);}else{++pos;}}

4。示例：

/***反映股票行情*/#include <iostream>#include <map>#include <string>using namespace std;int main(){typedef map<string,float> StringFloatMap;StringFloatMap stocks;stocks["BASF"] = 369.50;stocks["VW"] = 413.50;stocks["Daimler"]=819.00;stocks["BMW"] = 834.00;stocks["Siemens"]=842.20;StringFloatMap::iterator pos;for(pos=stocks.begin();pos!=stocks.end();++pos){cout<<"stock: "<<pos->first<<"\t"<<"price: "<<pos->second<<endl;}cout<<endl;for(pos=stocks.begin();pos!=stocks.end();++pos){pos->second*=2;}for(pos=stocks.begin();pos!=stocks.end();++pos){cout<<"stock: "<<pos->first<<"\t"<<"price: "<<pos->second<<endl;}cout<<endl;stocks["Volkswagen"]=stocks["VW"];stocks.erase("VW");for(pos=stocks.begin();pos!=stocks.end();++pos){cout<<"stock: "<<pos->first<<"\t"<<"price: "<<pos->second<<endl;}return 0;}

 

/***1.如何使用maps*2.如何撰写和使用仿函数(functor)*3.如何在执行期定义排序算法*4.如何在“不在乎大小写”的情况下比较字符串(strings)*/#include <iostream>#include <map>#include <string>#include <iomanip>#include <algorithm>using namespace std;class RuntimeStringCmp{public:enum cmp_mode{normal,nocase};private:const cmp_mode mode;static bool nocase_compare(char c1,char c2){return toupper(c1)<toupper(c2);}public:RuntimeStringCmp(cmp_mode m=normal):mode(m){}bool operator()(const string& s1,const string& s2)const{if(mode==normal){return s1<s2;}else{return lexicographical_compare(s1.begin(),s1.end(),s2.begin(),s2.end(),nocase_compare);//用于按字典序比较两个序列。}}};typedef map<string,string,RuntimeStringCmp> StringStringMap;void fillAndPrint(StringStringMap& coll);int main(){StringStringMap coll1;fillAndPrint(coll1);RuntimeStringCmp ignorecase(RuntimeStringCmp::nocase);StringStringMap coll2(ignorecase);fillAndPrint(coll2);return 0;}void fillAndPrint(StringStringMap& coll){coll["Deutschlan"]="Germany";coll["deutsch"]="German";coll["Haken"]="snag";coll["arbeiten"]="work";coll["Hund"]="dog";coll["gehen"]="go";coll["Unternehmen"]="enterprise";coll["unternehmen"]="undertake";coll["gehen"]="walk";coll["Bestatter"]="undertaker";StringStringMap::iterator pos;cout.setf(ios::left,ios::adjustfield);for(pos=coll.begin();pos!=coll.end();++pos){cout<<setw(15)<<pos->first.c_str()<<" "<<pos->second<<endl;}cout<<endl;}