auto_ptr的一个例子

 

例子：

#include <iostream>#include <string>#include <memory>using namespace std;int main(){std::string * str2 = new std::string("hello");auto_ptr<std::string> str1(str2);std::string * str3;std::cout << "string2: " << str2->length() << " string2 address: " << str2 << endl;std::cout << "string2: " << str1->c_str() << endl;//Returns a pointer to the object pointed by the auto_ptr object, if any, or zero if it does not point to any object.if(str1.get() == str2){std::cout << "str1 is an smart pointer!!! : " << str1.get() << endl;}else{std::cout << "str1 is NOT an smart pointer!!!" << endl;}//Sets the auto_ptr internal pointer to null pointer (which indicates it points to no object) without destructing the object currently pointed by the auto_ptr.//The function returns a pointer to the object it pointed before the call, which is no longer its responsibility to destruct.str3 = str1.release();if(str1.get() == str2){std::cout << "str1 is an smart pointer to str2" << endl;}else if(str1.get() == str3){std::cout << "str1 is an smart pointer to str3" << endl;}else{std::cout << "!!!!!!! : " << str1.get() << endl;}//Destructs the object pointed by the auto_ptr object, if any, and deallocates its memory (by calling operator delete). //If a value for p is specified, the internal pointer is initialized to that value (otherwise it is set to the null pointer).std::string * str4 = new std::string("world!");str1.reset(str4);std::cout << "str1 content after reset: " << str1->c_str() << endl;return 1;}

 

执行结果如下：

ewuming/morgan> ./a.out
string2: 5  string2 address: 0x804b008
string2: hello
str1 is an smart pointer!!! : 0x804b008
!!!!!!! : 0
str1 content after reset: world!

 

 

auto_ptr的根本原理：

智能指针的关键技术：在于构造栈上对象的生命期控制堆上构造的对象的生命期.因为在智能指针的内部,存储着堆对象的指针,而且在构析函数中调用delete行为。

 

如果几个auto_ptr指向同一个对象，那么，退出的时候，每个auto_ptr都会执行delete操作。程序最终crash。

 

smart pointer is smart, however, man is most of important.

 

 

 

Other experience:

1，auto_ptr存储的指针应该为NULL或者指向动态分配的内存块。

2，auto_ptr存储的指针应该指向单一物件（是new出来的，而不是new[]出来的）。

3，两个auto_ptr对象不会同时指向同一块内存块。要明白2个auto_ptr对象赋值会发生什么。

4，千万不要把auto_ptr对象放在容器中。

5，当将auto_ptr作为函数参数时，最好声明为const auto_ptr<T>&(by const ref).当函数返回值可以简单的传值（by value).

 

 

Web links:

http://blog.csdn.net/cyblueboy83/archive/2007/09/20/1792463.aspx