浅析map和multimap应用的小程序

创建类如下：

class Person{private:    char *name;    int age;    friend class lesserAge;public:    Person(const char *ch = NULL, int num = 0):age(num){  //1        name = new char[strlen(ch)+1];        strcpy(name, ch);        name[strlen(ch)] = '\0';        //cout << "name:" << name << endl;    }    Person(const Person &ps){  //2        name = new char[strlen(ps.name)+1];        strcpy(name,ps.name);        name[strlen(ps.name)] = '\0';        age = ps.age;    }    ~Person(){  //3        delete[] name;    }    bool operator<(const Person &p) const {        return strcmp(name, p.name) < 0;    }    friend ostream &operator<<(ostream &out, const Person &ps){  //4        out << "(" << ps.name << ", " << ps.age << ")";        return out;    }};class lesserAge{public:    int operator() (const Person &p1, const Person &p2) const {        return p1.age < p2.age;    }};

1. 构造函数：赋值的时候可能输入的值不完整，所以设定默认值，对于char *指针赋值的时候，要采用复制的方式，否则会造成指针指向同一块区域，在析构函数起作用的时候会形成野指针。
2. 这里要显示写出复制构造函数的原因一致，在用类对象构建其他对象的时候，如果采用隐式构造函数，会导致和上述一样的问题。
3. 析构函数，在有内存申请的时候，老样子^_^
4. 重载<<为了接下来打印使用。
   main函数里结构如下：

pair<Person, char *> p[] = {        pair<Person, char *>(Person("Gregg", 25), "Pittsburgh"),        pair<Person, char *>(Person("Ann", 30), "Boston"),        pair<Person, char *>(Person("Bill", 20), "Belmont")};    map<Person, char *> cities(p, p+3);  //1    map<Person, char *>::iterator it  = cities.begin();    cities[Person("Kay", 40)] = "New York";  //2    cities["Jenny"] = "Newark";  //3    cities.insert(map<Person, char *>::value_type(Person("Kay", 40), "Detroit"));  //4    cities.insert(pair<Person, char *>(Person("Kay", 40), "Austin"));    map<Person, char *>::iterator i;    for(i = cities.begin(); i != cities.end(); i++)        cout << (*i).first << ' ' << (*i).second << endl;

1. 构造map的方式之一，不多介绍
2. 以Person类型的对象为索引（可以看作广义上的数组）
3. 对应上面的构造函数，age为默认值0，此处意为在索引Person(“Jenny”, 0)处将内容置为”Newark”。
4. 以map< T, U >::value_type的类型构造对象

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完整代码如下：

#include <iostream>#include <cstring>#include <map>using namespace std;class Person{private:    char *name;    int age;    friend class lesserAge;public:    Person(const char *ch = NULL, int num = 0):age(num){        name = new char[strlen(ch)+1];        strcpy(name, ch);        name[strlen(ch)] = '\0';        //cout << "name:" << name << endl;    }    Person(const Person &ps){        name = new char[strlen(ps.name)+1];        strcpy(name,ps.name);        name[strlen(ps.name)] = '\0';        age = ps.age;    }    ~Person(){        delete[] name;    }    bool operator<(const Person &p) const {        return strcmp(name, p.name) < 0;    }    friend ostream &operator<<(ostream &out, const Person &ps){        out << "(" << ps.name << ", " << ps.age << ")";        return out;    }};class lesserAge{public:    int operator() (const Person &p1, const Person &p2) const {        return p1.age < p2.age;    }};int main(){    pair<Person, char *> p[] = {        pair<Person, char *>(Person("Gregg", 25), "Pittsburgh"),        pair<Person, char *>(Person("Ann", 30), "Boston"),        pair<Person, char *>(Person("Bill", 20), "Belmont")};    map<Person, char *> cities(p, p+3);    map<Person, char *>::iterator it  = cities.begin();    cities[Person("Kay", 40)] = "New York";    cities["Jenny"] = "Newark";    cities.insert(map<Person, char *>::value_type(Person("Kay", 40), "Detroit"));    cities.insert(pair<Person, char *>(Person("Kay", 40), "Austin"));    map<Person, char *>::iterator i;    for(i = cities.begin(); i != cities.end(); i++)        cout << (*i).first << ' ' << (*i).second << endl;    cout << "-------------------------------------" << endl;    cities[p[1].first] = "Chicago";    multimap<Person, char *> mCities(p, p+3);    mCities.insert(pair<Person, char *>(Person("Kay", 40), "Austin"));    mCities.insert(pair<Person, char *>(Person("Kay", 40), "Austin"));    mCities.insert(pair<Person, char *>(Person("Kay", 40), "Detroit"));    multimap<Person, char *>::iterator mi;    for(mi = mCities.begin(); mi != mCities.end(); mi++)        cout << mi->first << ' ' << mi->second << endl;    cout << "-------------------------------------" << endl;    (*(mCities.find(Person("Kay", 40)))).second = "New York";    for(mi = mCities.begin(); mi != mCities.end(); mi++)        cout << mi->first << ' ' << mi->second << endl;    return 0;}