Boost: asio (2): shared

This should start with a smart pointer. A smart pointer is to dynamically manage a pointer using the construction and destructor of a variable. To put it bluntly, construct -- new; destructor -- delete. We can easily write a smart pointer: templateclassTclassTAutoPtr {public: TAutoPtr () {m_tnewT (); coutTAutoPtr: TAutoPt

This should start with a smart pointer. A smart pointer is to dynamically manage a pointer using the construction and destructor of a variable. To put it bluntly, construct -- new; destructor -- delete. We can easily write a smart pointer: template class Tclass TAutoPtr {public: TAutoPtr () {m_t = new T (); cout TAutoPtr: TAutoPt

This should start with a smart pointer. A smart pointer is to dynamically manage a pointer using the construction and destructor of a variable.

To put it bluntly, construct --> new; destructor --> delete

We can easily write a smart pointer:

template 
 
  class TAutoPtr{public:    TAutoPtr() {        m_t = new T();        cout << "TAutoPtr::TAutoPtr()" << endl;    }    ~TAutoPtr() {        delete m_t;        cout << "TAutoPtr::~TAutoPtr()" << endl;    }private:    T*  m_t;};
 

Usage:

int main(int argc, char** argv){    TAutoPtr
 
   tt;        return 0;}
 

This is okay.

Boost: asio provides this method, allowing shared_ptr to quickly manage your class.

However, this causes a problem. When your class is derived from enable_shared_from_this, you cannot use shared_from_this () in the class member function to obtain class pointers.

The following is an error:

class B { public:     B(): x_(4) {         cout << "B::B()" << endl;     }     ~B() {         cout << "B::~B()" << endl;     }     void f() {         shared_ptr p(this);         cout << p->x_ << endl;     } private:     int x_; }; int main(int argc, char** argv) {     shared_ptr x(new B);     x->f();     return 0; } 

Output:

B: B ()
4
B ::~ B ()
B ::~ B ()

The same object is analyzed twice, causing catastrophic consequences.

Similarly, the following usage is also incorrect:

class A : public enable_shared_from_this { public:     A() {         cout << "A::A()" << endl;     }     ~A() {         cout << "A::~A()" << endl;     }     void f() {         //cout << shared_from_this()->x_ << endl; // this way is okay too        shared_from_this();        //shared_ptr p = shared_from_this();        //cout << p->x_ << endl;    }private:    int x_;};int main(int argc, char** argv){    A* aa = new A();    aa->f();        return 0;}

Although we have sent the Class A to enable_shared_from_this, shared_ptr Class A is not used. It is also incorrect.

Summary:

1. This class is derived from enable_shared_from_this. Example: class A: public enable_shared_from_this

2. shared_ptr abc (new A () must be added for use ())