BOOST Library (1)

class implementation
{
public:
~implementation() { std::cout <<"destroying implementation\n"; }
void do_something() { std::cout << "did something\n"; }
};

void test()
{
boost::shared_ptr<implementation> sp1(new implementation());
std::cout<<"The Sample now has "<<sp1.use_count()<<" references\n";

boost::shared_ptr<implementation> sp2 = sp1;
std::cout<<"The Sample now has "<<sp2.use_count()<<" references\n";

sp1.reset();
std::cout<<"After Reset sp1. The Sample now has "<<sp2.use_count()<<" references\n";

sp2.reset();
std::cout<<"After Reset sp2.\n";
}

程序输出内容：
The Sample now has 1 references
The Sample now has 2 references
After Reset sp1. The Sample now has 1 references
destroying implementation
After Reset sp2.

归纳如下：
Shared_pt可以共享内存，两个Shared_ptr之间直接用“=”赋值，每个Shared_ptr内部都有一个计数器记录该内存地址有多少个Shared_ptr持有，可以用use_count()访问。当该计数器为0时，会自动调用delete删除内存。