class student{private: string name; char gender;public: student(string n,char g):name(n),gender(g){} //初始化列表使屬性一次性賦值完畢，否則需要兩次 friend ostream& operator<<(ostream& cout,student &s); //定義為friend便可擁有訪問private屬性的許可權};

ostream& operator<<(ostream& cout,student &s){ cout<<s.name<<" "<<s.gender; return cout;}

在寫主函式

int main(){ map<string,student> sm; student ts("lishuai","M"); sm[“001”] = ts;//檢索key=”001”的值，如果存在，用ts覆蓋，如果不存在，插入ts for(map<string,student>::iterator it = sm.begin();it!=sm.end();it++) { cout<<(*it).second<<endl;呼叫operaotr<<過載函式列印student物件 } system("pause"); return 0;}

執行報了一堆錯：後來發現最根本問題是無法找到student()無參建構函式。於是在類中新增建構函式

student(){}

後執行正確。結果為

lishuai M

說明在插入過程中，如果沒找到物件，就先呼叫無參建構函式。但這隻能構造一個空的物件，那一定還會呼叫賦值函式填寫其屬性，賦值函式是編譯器自動為我們寫的，為了搞清楚這個具體過程，我自己來實現。

class student

{

private:

string name;

char gender;

public:

student(){cout<<"Default Constructor"<<endl; name="---------";}//給個空名字

student(string n,char g):name(n),gender(g){cout<<"Constructor:"<<name<<endl;}

student& operator=(const student& s);

student(const student& s);

~student(){cout<<"Destructor:"<<this->name<<endl;}

friend ostream& operator<<(ostream& cout,student &s);

};

student& student::operator=(const student& s)

{

cout<<"Assignment:"<<s.name<<endl;

this->name = s.name;

this->gender = s.gender;

return *this;

}

student::student(const student& s)

{

static char c="a";

this->name = s.name+c++; //每呼叫一次，就改變名字

this->gender = s.gender;

cout<<"Copy Constructor:"<<this->name<<endl;

}

ostream& operator<<(ostream& cout,student &s)

{

cout<<s.name<<" "<<s.gender;

return cout;

}

int main()

{

map<string,student> sm;

student ts("lishuai","M");

cout<<"begin"<<endl;

sm["001"]=ts;

cout<<"end"<<endl;

for(map<string,student>::iterator it = sm.begin();it!=sm.end();it++)

{

cout<<(*it).second<<endl;

}

system("pause");

return 0;

}

執行結果：

Constructor:lishuai

begin

Default Constructor //構造空物件1

Copy Constructor:---------a //構造空物件2

Copy Constructor:---------ab //構造空物件3

Destructor:---------a //析構空物件2

Destructor:--------- //析構空物件1

Assignment:lishuai //給物件3賦值

end

lishuai M

可以看到，在插入的過程中，首先呼叫1次無參建構函式，然後呼叫2次複製建構函式依次複製前一個建立的物件，再呼叫兩次解構函式析構頭2個空物件，最後呼叫一次賦值函式。