boost 智能指针 shared_ptr

#include 
#include <boost/shared_ptr.hpp>
using namespace std;
class MyClass
{
public:
void func()
{
cout << “MyClass func” << endl;
}
};
class Mem_malloc
{
public:
Mem_malloc()
{
m_int = (int*)malloc(sizeof(int) * 1024 * 1024 * 100); // 400M
}
~Mem_malloc()
{
free(m_int);
}
private:
int* m_int;
};
int main(int argc, char* argv[])
{
// 两种构造
boost::shared_ptr ptr;
boost::shared_ptr ptr_arr(new int(100));
// 与普通指针相差无几
int a = 111;
int* pA = &a;
cout << “*pA = “ << *pA << endl;
cout << “*ptr_arr = “ << *ptr_arr << endl;
// 操作对象
boost::shared_ptr ptr_obj;
boost::shared_ptr ptr_MyClass(new MyClass());
ptr_obj = ptr_MyClass;
ptr_obj->func();
// 智能指针避免普通指针和智能指针混用
// 防止智能指针计数器为0将内存释放后，普通指针就变了野指针。
int* p_int001 = new int(100);
int* p_int002 = p_int001;
//boost::shared_ptr ptr_int003 = p_int002;// 错误的，不能混用
boost::shared_ptr ptr_int004(new int(100));
//int* p_int005 = ptr_int004;// 错误的，不能混用
// 引用计数
boost::shared_ptr ptr_obj001(new MyClass());
cout << ptr_obj001.use_count() << endl;
boost::shared_ptr ptr_obj002 = ptr_obj001;
// 指向同一对象时，两个智能指针的引用计数都会增加
cout << ptr_obj002.use_count() << endl;
cout << ptr_obj001.use_count() << endl;
{
// 新作用域指向同一对象，同样会自增引用计数
boost::shared_ptr ptr_obj003 = ptr_obj001;
cout << “new function” << endl;
cout << “ptr_obj003.use_count() = “ << ptr_obj003.use_count() << endl;
cout << “ptr_obj002.use_count() = “ << ptr_obj002.use_count() << endl;
cout << “ptr_obj001.use_count() = “ << ptr_obj001.use_count() << endl;
}
// 离开作用域后，原作用域内的引用计数会被减去
cout << “exit function” << endl;
cout << “ptr_obj002.use_count() = “ << ptr_obj002.use_count() << endl;
cout << “ptr_obj001.use_count() = “ << ptr_obj001.use_count() << endl;
// 测试智能指针是否会释放内存
{
cout << “准备分配内存” << endl;
// 这个过程打开任务管理器，按下任意键后看内存的变化
system(“pause”);
boost::shared_ptr<Mem_malloc> ptr_obj004(new Mem_malloc());
cout << “准备释放内存” << endl;
// 离开作用域后再看内存的变化
system(“pause”);
// 离开作用域后会自动释放ptr_obj004指向的内存，在任务管理器中，可以明显的看到我们进程内存的变化
}
return 0;
}