【17】c++11新特性 —＞弱引用智能指针weak_ptr（2）

返回管理this的shared_ptr

通过wek_ptr返回管理this资源的共享智能指针对象shared_ptr。C++11中为我们提供了一个模板类叫做std::enable_shared_from_this，这个类中有一个方法叫做shared_from_this()，通过这个方法可以返回一个共享智能指针，在函数的内部就是使用weak_ptr来监测this对象，并通过调用weak_ptr的lock()方法返回一个shared_ptr对象。

#include <iostream>
#include <memory>
using namespace std;struct Test : public enable_shared_from_this<Test>
{shared_ptr<Test> getSharedPtr(){return shared_from_this();}~Test(){cout << "class Test is disstruct ..." << endl;}
};int main()
{shared_ptr<Test> sp1(new Test);cout << "use_count: " << sp1.use_count() << endl;shared_ptr<Test> sp2 = sp1->getSharedPtr();cout << "use_count: " << sp1.use_count() << endl;return 0;
}

循环引用的案例

#include <iostream>
#include <memory>
using namespace std;struct TA;
struct TB;struct TA
{shared_ptr<TB> bptr;~TA(){cout << "class TA is disstruct ..." << endl;}
};struct TB
{shared_ptr<TA> aptr;~TB(){cout << "class TB is disstruct ..." << endl;}
};void testPtr()
{shared_ptr<TA> ap(new TA);shared_ptr<TB> bp(new TB);cout << "TA object use_count: " << ap.use_count() << endl;cout << "TB object use_count: " << bp.use_count() << endl;ap->bptr = bp;bp->aptr = ap;cout << "TA object use_count: " << ap.use_count() << endl;cout << "TB object use_count: " << bp.use_count() << endl;
}int main()
{testPtr();return 0;
}

修改

#include <iostream>
#include <memory>
using namespace std;struct TA;
struct TB;struct TA
{weak_ptr<TB> bptr;~TA(){cout << "class TA is disstruct ..." << endl;}
};struct TB
{shared_ptr<TA> aptr;~TB(){cout << "class TB is disstruct ..." << endl;}
};void testPtr()
{shared_ptr<TA> ap(new TA);shared_ptr<TB> bp(new TB);cout << "TA object use_count: " << ap.use_count() << endl;cout << "TB object use_count: " << bp.use_count() << endl;ap->bptr = bp;bp->aptr = ap;cout << "TA object use_count: " << ap.use_count() << endl;cout << "TB object use_count: " << bp.use_count() << endl;
}int main()
{testPtr();return 0;
}