设计模式观后（c++还原之二十五 享元模式）

string int2string(int n) {
char buffer[10] = {0};
_itoa_s(n, buffer, 10, 10);
return string(buffer);
}
//享元模式
//作者例子：报考系统的对象
//每个用户的访问就构造一个对象会导致内存不够，作者设立关键字：多个用户使用一块内存
//报考信息
class SignInfo {
private:
string m_strID;//报名的ID
string m_strLocation;//考试地点
string m_strSubject;//考试科目

public:
string GetID() {return m_strID;}
void SetID(string id) {m_strID = id;}

string GetLocation() {return m_strLocation;}
void SetLocation(string location) {m_strLocation = location;}

string GetSubject() {return m_strSubject;}
void SetSubject(string subject) {m_strSubject = subject;}
};
//带对象池的报考信息
class SignInfoPool : public SignInfo {
//定义对象池的key
private:
string m_strKey;
public:
SignInfoPool(string key) {
m_strKey = key;
}
string GetKey() {
return m_strKey;
}
void SetKey(string key) {
m_strKey = key;
}
};
//对象池的工厂类
class SignInfoFactory {
private:
//池容器
static map<string, SignInfo*> s_pool;
public:
static SignInfo* SignInfo() {
return new class SignInfo;
}
//从线程池获取对象
static class SignInfo* GetSignInfo(string key) {
class SignInfo* result = NULL;
//池中没有对象，则建立，并放入。有就返回
if (s_pool.find(key) != s_pool.end()) {
cout << "直接从池中取出" <<endl;
result = s_pool[key];
} else {
cout << "建立对象，放置池中" << endl;
result = new SignInfoPool(key);
s_pool.insert(make_pair(key, result));
}
return result;
}
};
map<string, SignInfo*> SignInfoFactory::s_pool;

class Client {
public:
static void main() {
//初始化对象池
for (int i = 0; i < 4; i++)
{
string subject = "科目" + int2string(i);
for (int j = 0; j < 3; j++)
{
string key = subject + "考试地点";
key += int2string(j);
cout << key <<":";
SignInfoFactory::GetSignInfo(key);
}
}
SignInfo* p_signinfo = SignInfoFactory::GetSignInfo("科目1考试地点1");
}
};
//key值是唯一的，作者根据这个而建立对象
//通过唯一值访问对象