设计模式简单代码之Flyweight模式
2008-08-27 09:30
537 查看
在一雨田的Blog有一篇关于Flyweight模式的文章： http://blog.csdn.net/dylgsy/archive/2006/08/10/1045678.aspx
但在编译运行时，问题产生了：出版社和作者显示不了。
一雨田原来的代码：
// Flyweight.cpp
#pragma warning(disable: 4786)
#include <iostream>
#include <map>
#include <string>
#include <stdlib.h>
using namespace std;
class Book
{
public:
string GetPublish() {return *m_publishCompany;}
string GetWriter() {return *m_writer;}
int GetBookID() {return m_bookID;}
int GetPrice() {return m_price;}
string GetName() {return m_name;}
void SetPublish(string *s) {m_publishCompany = s;}
void SetWriter(string *s) {m_writer = s;}
void SetBookID(int id) {m_bookID = id;}
void SetPrice(int price) {m_price = price;}
void SetName(string &s) {m_name = s;}
private:
string *m_publishCompany; // 出版社
string *m_writer; // 作者
int m_bookID; // 书籍编号
int m_price; // 价钱
string m_name; // 书名
};
class PublishFlyweight
{
public:
PublishFlyweight(string s)
{
m_name = s;
}
string GetName()
{
return m_name;
}
private:
string m_name;
};
class PublishFlyweightFactory
{
public:
PublishFlyweight* GetPublish(string key)
{
PublishFlyweight *p;
map<string, PublishFlyweight*>::iterator it;
it = mapPublish.find(key);
// 存在这个出版社
if(it != mapPublish.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, PublishFlyweight*> 的 PublishFlyweight*
p = (*it).second;
cout << "已经有这个出版社: " << p->GetName() << " 你节省了" << strlen(p->GetName().c_str()) << "字节的空间" << endl;
}
else
{// 插入这个PublishFlyweight
p = new PublishFlyweight(key);
mapPublish[key] = p;
}
return p;
}
private:
map<string, PublishFlyweight*> mapPublish;
};
class WriterFlyweight
{
public:
WriterFlyweight(string s)
{
m_name = s;
}
string GetName()
{
return m_name;
}
private:
string m_name;
};
class WriterFlyweightFactory
{
public:
WriterFlyweight* GetWriter(string key)
{
WriterFlyweight *p;
map<string, WriterFlyweight*>::iterator it;
it = mapWriter.find(key);
// 存在这个Writer
if(it != mapWriter.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, WriterFlyweight*> 的 WriterFlyweight*
p = (*it).second;
cout << "已经有这个作者名字: " << p->GetName() << " 你节省了" << strlen(p->GetName().c_str()) << "字节的空间" << endl;
}
else
{// 插入这个PublishFlyweight
p = new WriterFlyweight(key);
mapWriter[key] = p;
}
return p;
}
private:
map<string, WriterFlyweight*> mapWriter;
};
void ShowBookInfo(Book book)
{
cout << "书名：" << book.GetName() << endl;
cout << "编号：" << book.GetBookID() << endl;
cout << "价钱：" << book.GetPrice() << endl;
cout << "出版：" << book.GetPublish() << endl;
cout << "作者：" << book.GetWriter() << endl;
cout << endl;
}
void main()
{
PublishFlyweightFactory pff;
WriterFlyweightFactory wff;
Book book1, book2, book3;
book1.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );
book1.SetWriter( &(wff.GetWriter("候捷")->GetName()) );
book1.SetBookID(0000);
book1.SetPrice(20);
book1.SetName(string("<<C++好野>>"));
ShowBookInfo(book1);
book2.SetPublish( &(pff.GetPublish("人民邮电出版社")->GetName()) );
book2.SetWriter( &(wff.GetWriter("候捷")->GetName()) );
book2.SetBookID(0001);
book2.SetPrice(30);
book2.SetName(string("<<C++是好劲>>"));
ShowBookInfo(book2);
book3.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );
book3.SetWriter( &(wff.GetWriter("一雨田")->GetName()) );
book3.SetBookID(0002);
book3.SetPrice(50);
book3.SetName(string("<<C++无得顶，我是铁头功...>>"));
ShowBookInfo(book3);
system("pause");
}
是什么原因呢？仔细分析其源代码，发现“book1.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );”这一行使用了临时变量，在取“pff.GetPublish("机械工业出版社")->GetName() ”返回一个临时变量，而再取临时变量的地址&，运行到下一行时，这个临时地址将变成一个无效的地址，指向任何值都可以出现。因此，编程中是严禁这样使用的，编程时都应注意此类问题。修改好的代码如下：
/*
来源：一雨田Blog
问题：出版社和作者显示不了
修改：qmroom
*/
// Flyweight.cpp
#include <iostream>
#include <map>
#include <string>
#include <stdlib.h>
using namespace std;
typedef char CHAR;
typedef CHAR *LPSTR;
typedef const CHAR *LPCSTR;
class Book
{
public:
string GetPublish() {return *m_publishCompany;}
string GetWriter() {return *m_writer;}
int GetBookID() {return m_bookID;}
int GetPrice() {return m_price;}
string GetName() {return m_name;}
void SetPublish(string *s) {m_publishCompany = s;}
void SetWriter(string *s) {m_writer = s;}
void SetBookID(int id) {m_bookID = id;}
void SetPrice(int price) {m_price = price;}
void SetName(LPCSTR s) {m_name = s;}
private:
string *m_publishCompany; // 出版社
string *m_writer; // 作者
int m_bookID; // 书籍编号
int m_price; // 价钱
string m_name; // 书名
};
class PublishFlyweight
{
public:
PublishFlyweight(string s)
{
m_name = new string(s);
}
virtual ~PublishFlyweight()
{
delete(m_name);
}
string *GetName()
{
return m_name;
}
private:
string *m_name;
};
class PublishFlyweightFactory
{
public:
PublishFlyweight* GetPublish(string key)
{
PublishFlyweight *p;
map<string, PublishFlyweight*>::iterator it;
it = mapPublish.find(key);
// 存在这个出版社
if(it != mapPublish.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, PublishFlyweight*> 的 PublishFlyweight*
p = (*it).second;
cout << "已经有这个出版社: " << *(p->GetName()) << " 你节省了" << strlen((*(p->GetName())).c_str()) << "字节的空间" << endl;
}
else
{
// 插入这个PublishFlyweight
p = new PublishFlyweight(key);
mapPublish[key] = p;
}
return p;
}
private:
map<string, PublishFlyweight*> mapPublish;
};
class WriterFlyweight
{
public:
WriterFlyweight(string s)
{
m_name = new string(s);
}
virtual ~WriterFlyweight()
{
delete(m_name);
}
string *GetName()
{
return m_name;
}
private:
string *m_name;
};
class WriterFlyweightFactory
{
public:
WriterFlyweight* GetWriter(string key)
{
WriterFlyweight *p;
map<string, WriterFlyweight*>::iterator it;
it = mapWriter.find(key);
// 存在这个Writer
if(it != mapWriter.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, WriterFlyweight*> 的 WriterFlyweight*
p = (*it).second;
cout << "已经有这个作者名字: " << *(p->GetName()) << " 你节省了" << strlen((*(p->GetName())).c_str()) << "字节的空间" << endl;
}
else
{
// 插入这个PublishFlyweight
p = new WriterFlyweight(key);
mapWriter[key] = p;
}
return p;
}
private:
map<string, WriterFlyweight*> mapWriter;
};
void ShowBookInfo(Book book)
{
cout << "书名：" << book.GetName() << endl;
cout << "编号：" << book.GetBookID() << endl;
cout << "价钱：" << book.GetPrice() << endl;
cout << "出版：" << book.GetPublish() << endl;
cout << "作者：" << book.GetWriter() << endl;
cout << endl;
}
void main()
{
PublishFlyweightFactory pff;
WriterFlyweightFactory wff;
Book book1, book2, book3;
book1.SetPublish( pff.GetPublish("机械工业出版社")->GetName() );
book1.SetWriter( wff.GetWriter("qmroom")->GetName() );
book1.SetBookID(0000);
book1.SetPrice(20);
book1.SetName(("<<C++好野>>"));
ShowBookInfo(book1);
book2.SetPublish( pff.GetPublish("人民邮电出版社")->GetName() );
book2.SetWriter( wff.GetWriter("qmroom")->GetName() );
book2.SetBookID(0001);
book2.SetPrice(30);
book2.SetName(("<<C++是好劲>>"));
ShowBookInfo(book2);
book3.SetPublish( pff.GetPublish("机械工业出版社")->GetName() );
book3.SetWriter( wff.GetWriter("一雨田")->GetName() );
book3.SetBookID(0002);
book3.SetPrice(50);
book3.SetName(("<<C++无得顶，我是铁头功...>>"));
ShowBookInfo(book3);
system("pause");
}
其实，这段代码还有很多可以修改的地方，以便提高性能和便于维护和使用。请看设计模式简单代码之Flyweight模式（二）。
下一篇
但在编译运行时，问题产生了：出版社和作者显示不了。
一雨田原来的代码：
// Flyweight.cpp
#pragma warning(disable: 4786)
#include <iostream>
#include <map>
#include <string>
#include <stdlib.h>
using namespace std;
class Book
{
public:
string GetPublish() {return *m_publishCompany;}
string GetWriter() {return *m_writer;}
int GetBookID() {return m_bookID;}
int GetPrice() {return m_price;}
string GetName() {return m_name;}
void SetPublish(string *s) {m_publishCompany = s;}
void SetWriter(string *s) {m_writer = s;}
void SetBookID(int id) {m_bookID = id;}
void SetPrice(int price) {m_price = price;}
void SetName(string &s) {m_name = s;}
private:
string *m_publishCompany; // 出版社
string *m_writer; // 作者
int m_bookID; // 书籍编号
int m_price; // 价钱
string m_name; // 书名
};
class PublishFlyweight
{
public:
PublishFlyweight(string s)
{
m_name = s;
}
string GetName()
{
return m_name;
}
private:
string m_name;
};
class PublishFlyweightFactory
{
public:
PublishFlyweight* GetPublish(string key)
{
PublishFlyweight *p;
map<string, PublishFlyweight*>::iterator it;
it = mapPublish.find(key);
// 存在这个出版社
if(it != mapPublish.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, PublishFlyweight*> 的 PublishFlyweight*
p = (*it).second;
cout << "已经有这个出版社: " << p->GetName() << " 你节省了" << strlen(p->GetName().c_str()) << "字节的空间" << endl;
}
else
{// 插入这个PublishFlyweight
p = new PublishFlyweight(key);
mapPublish[key] = p;
}
return p;
}
private:
map<string, PublishFlyweight*> mapPublish;
};
class WriterFlyweight
{
public:
WriterFlyweight(string s)
{
m_name = s;
}
string GetName()
{
return m_name;
}
private:
string m_name;
};
class WriterFlyweightFactory
{
public:
WriterFlyweight* GetWriter(string key)
{
WriterFlyweight *p;
map<string, WriterFlyweight*>::iterator it;
it = mapWriter.find(key);
// 存在这个Writer
if(it != mapWriter.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, WriterFlyweight*> 的 WriterFlyweight*
p = (*it).second;
cout << "已经有这个作者名字: " << p->GetName() << " 你节省了" << strlen(p->GetName().c_str()) << "字节的空间" << endl;
}
else
{// 插入这个PublishFlyweight
p = new WriterFlyweight(key);
mapWriter[key] = p;
}
return p;
}
private:
map<string, WriterFlyweight*> mapWriter;
};
void ShowBookInfo(Book book)
{
cout << "书名：" << book.GetName() << endl;
cout << "编号：" << book.GetBookID() << endl;
cout << "价钱：" << book.GetPrice() << endl;
cout << "出版：" << book.GetPublish() << endl;
cout << "作者：" << book.GetWriter() << endl;
cout << endl;
}
void main()
{
PublishFlyweightFactory pff;
WriterFlyweightFactory wff;
Book book1, book2, book3;
book1.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );
book1.SetWriter( &(wff.GetWriter("候捷")->GetName()) );
book1.SetBookID(0000);
book1.SetPrice(20);
book1.SetName(string("<<C++好野>>"));
ShowBookInfo(book1);
book2.SetPublish( &(pff.GetPublish("人民邮电出版社")->GetName()) );
book2.SetWriter( &(wff.GetWriter("候捷")->GetName()) );
book2.SetBookID(0001);
book2.SetPrice(30);
book2.SetName(string("<<C++是好劲>>"));
ShowBookInfo(book2);
book3.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );
book3.SetWriter( &(wff.GetWriter("一雨田")->GetName()) );
book3.SetBookID(0002);
book3.SetPrice(50);
book3.SetName(string("<<C++无得顶，我是铁头功...>>"));
ShowBookInfo(book3);
system("pause");
}
是什么原因呢？仔细分析其源代码，发现“book1.SetPublish( &(pff.GetPublish("机械工业出版社")->GetName()) );”这一行使用了临时变量，在取“pff.GetPublish("机械工业出版社")->GetName() ”返回一个临时变量，而再取临时变量的地址&，运行到下一行时，这个临时地址将变成一个无效的地址，指向任何值都可以出现。因此，编程中是严禁这样使用的，编程时都应注意此类问题。修改好的代码如下：
/*
来源：一雨田Blog
问题：出版社和作者显示不了
修改：qmroom
*/
// Flyweight.cpp
#include <iostream>
#include <map>
#include <string>
#include <stdlib.h>
using namespace std;
typedef char CHAR;
typedef CHAR *LPSTR;
typedef const CHAR *LPCSTR;
class Book
{
public:
string GetPublish() {return *m_publishCompany;}
string GetWriter() {return *m_writer;}
int GetBookID() {return m_bookID;}
int GetPrice() {return m_price;}
string GetName() {return m_name;}
void SetPublish(string *s) {m_publishCompany = s;}
void SetWriter(string *s) {m_writer = s;}
void SetBookID(int id) {m_bookID = id;}
void SetPrice(int price) {m_price = price;}
void SetName(LPCSTR s) {m_name = s;}
private:
string *m_publishCompany; // 出版社
string *m_writer; // 作者
int m_bookID; // 书籍编号
int m_price; // 价钱
string m_name; // 书名
};
class PublishFlyweight
{
public:
PublishFlyweight(string s)
{
m_name = new string(s);
}
virtual ~PublishFlyweight()
{
delete(m_name);
}
string *GetName()
{
return m_name;
}
private:
string *m_name;
};
class PublishFlyweightFactory
{
public:
PublishFlyweight* GetPublish(string key)
{
PublishFlyweight *p;
map<string, PublishFlyweight*>::iterator it;
it = mapPublish.find(key);
// 存在这个出版社
if(it != mapPublish.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, PublishFlyweight*> 的 PublishFlyweight*
p = (*it).second;
cout << "已经有这个出版社: " << *(p->GetName()) << " 你节省了" << strlen((*(p->GetName())).c_str()) << "字节的空间" << endl;
}
else
{
// 插入这个PublishFlyweight
p = new PublishFlyweight(key);
mapPublish[key] = p;
}
return p;
}
private:
map<string, PublishFlyweight*> mapPublish;
};
class WriterFlyweight
{
public:
WriterFlyweight(string s)
{
m_name = new string(s);
}
virtual ~WriterFlyweight()
{
delete(m_name);
}
string *GetName()
{
return m_name;
}
private:
string *m_name;
};
class WriterFlyweightFactory
{
public:
WriterFlyweight* GetWriter(string key)
{
WriterFlyweight *p;
map<string, WriterFlyweight*>::iterator it;
it = mapWriter.find(key);
// 存在这个Writer
if(it != mapWriter.end() )
{
// 这里可能有点难懂，请查阅ＳＴＬ的帮助文档
// 其实second就是指 map<string, WriterFlyweight*> 的 WriterFlyweight*
p = (*it).second;
cout << "已经有这个作者名字: " << *(p->GetName()) << " 你节省了" << strlen((*(p->GetName())).c_str()) << "字节的空间" << endl;
}
else
{
// 插入这个PublishFlyweight
p = new WriterFlyweight(key);
mapWriter[key] = p;
}
return p;
}
private:
map<string, WriterFlyweight*> mapWriter;
};
void ShowBookInfo(Book book)
{
cout << "书名：" << book.GetName() << endl;
cout << "编号：" << book.GetBookID() << endl;
cout << "价钱：" << book.GetPrice() << endl;
cout << "出版：" << book.GetPublish() << endl;
cout << "作者：" << book.GetWriter() << endl;
cout << endl;
}
void main()
{
PublishFlyweightFactory pff;
WriterFlyweightFactory wff;
Book book1, book2, book3;
book1.SetPublish( pff.GetPublish("机械工业出版社")->GetName() );
book1.SetWriter( wff.GetWriter("qmroom")->GetName() );
book1.SetBookID(0000);
book1.SetPrice(20);
book1.SetName(("<<C++好野>>"));
ShowBookInfo(book1);
book2.SetPublish( pff.GetPublish("人民邮电出版社")->GetName() );
book2.SetWriter( wff.GetWriter("qmroom")->GetName() );
book2.SetBookID(0001);
book2.SetPrice(30);
book2.SetName(("<<C++是好劲>>"));
ShowBookInfo(book2);
book3.SetPublish( pff.GetPublish("机械工业出版社")->GetName() );
book3.SetWriter( wff.GetWriter("一雨田")->GetName() );
book3.SetBookID(0002);
book3.SetPrice(50);
book3.SetName(("<<C++无得顶，我是铁头功...>>"));
ShowBookInfo(book3);
system("pause");
}
其实，这段代码还有很多可以修改的地方，以便提高性能和便于维护和使用。请看设计模式简单代码之Flyweight模式（二）。
下一篇
内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理 
相关文章推荐
- 设计模式简单代码之Flyweight模式（二）
- 设计模式简单代码之Flyweight模式
- 设计模式简单代码之Flyweight模式
- 设计模式简单代码之Flyweight模式
- Delphi 设计模式：《HeadFirst设计模式》Delphi7代码---工厂模式之简单工厂
- PHP设计模式之单例模式简单代码介绍
- 设计模式简单代码之Composite模式
- 23种设计模式及简单代码
- 设计模式简单代码之Mediator模式（二）
- 设计模式简单代码之Mediator模式
- 设计模式简单代码之Facade模式(编译系统篇)
- 设计模式简单代码之Chain Of Responsibility 模式(小孩要苹果篇)
- 设计模式简单代码之Command模式(皇帝圣旨篇)
- 设计模式简单代码之Proxy模式(买房子篇)
- 设计模式简单代码之Composite模式(老师分配任务篇)
- 请用代码简单描述一下Singleton、抽象工厂、Bridge、Composite（任选三个）的设计模式的概念
- 简单了解设计模式中的装饰者模式及C++版代码实现
- 设计模式思路和简单代码实现
- 设计模式简单代码之State模式
- 设计模式简单代码之Template Method模式(追MM篇)