最近在做Windows上管理USB手机终端的相关程序。
实际情况:
Class Phone *symbian = new Phone();
Class ConnectManager, Class CommManager都需要对symbian指针进行引用和维护(保留一个拷贝)。
但是这样就导致了symbian何时可以被delete?
在ConnectManager析构函数中delete? 这将导致CommManager无法使用symbian了。
在CommManager中delete symbian也是同样的道理。
在参考了《C++ Primer》之后,自己动手写一个智能指针
代码如下
#include <iostream>
using namespace std;
class ConnectManager;
class CommManager;
class Phone
{
public:
Phone() { cout << "Hello World!" << endl; }
~Phone() { cout << "Bye!" << endl; }
};
class U_ptr
{
friend class ConnectManager;
friend class CommManager;
public:
U_ptr(Phone *pH): use(0), pPhone(pH) { }
~U_ptr() { delete pPhone; }
private:
Phone *pPhone;//这里是关键,转移数据的宿主
size_t use;
};
class ConnectManager
{
public:
ConnectManager(U_ptr *p): pUptr(p)
{
++pUptr->use;
cout << "ConnectManager: Hi I get the Phone" << endl;
cout << pUptr->use << " users" << endl;
}
~ConnectManager()
{
cout << "ConnectManaer: Can I delete the Phone?" << endl;
if (--pUptr->use == 0)
{
cout << "Yes, You can" << endl;
delete pUptr;
}
else
{
cout << "No, You can't, The Phone is in use" << endl;
cout << pUptr->use << " users" << endl;
}
}
private:
U_ptr *pUptr;
};
class CommManager
{
public:
CommManager(U_ptr *p): pUptr(p)
{
++pUptr->use;
cout << "CommManager: Hi I get the Phone" << endl;
cout << pUptr->use << " users" << endl;
}
~CommManager()
{
cout << "CommManager: Can I delete the Phone" << endl;
if (--pUptr->use == 0)
{
cout << "Yes, You can" << endl;
}
else
{
cout << "No, You can't. The Phone is in use" << endl;
cout << pUptr->use << " users" << endl;
}
}
private:
U_ptr *pUptr;
};
int main(void)
{
Phone *symbian = new Phone();
U_ptr *pU = new U_ptr(symbian);
ConnectManager connManager = ConnectManager(pU);
CommManager commManager = CommManager(pU);
}
运行结果如下:
Hello World!
ConnectManager: Hi I get the Phone
1 users
CommManager: Hi I get the Phone
2 users
CommManager: Can I delete the Phone?
No, You Can't. The Phone is in use;
1 users
ConnectManager: Can I delete the Phone?
Yes. You can
Bye!
代码中已经注释出来了。智能指针的关键是转交数据的宿主。虽然Phone是给CommManager和ConnectManager使用,
但是,真正的Phone要由智能指针类去维护。