Punteros compartidos:
un std::shared_ptr es un contenedor para punteros sin procesar. Es un modelo de propiedad de recuento de referencias, es decir, mantiene el recuento de referencias de su puntero contenido en cooperación con todas las copias de std::shared_ptr. Por lo tanto, el contador se incrementa cada vez que un nuevo puntero apunta al recurso y se reduce cuando se llama al destructor del objeto.
Recuento de referencias:
es una técnica para almacenar el número de referencias, punteros o identificadores de un recurso, como un objeto, bloque de memoria, espacio en disco u otros recursos.
Un objeto al que hace referencia el puntero sin formato contenido no se destruirá hasta que el recuento de referencias sea mayor que cero, es decir, hasta que se hayan eliminado todas las copias de std::shared_ptr.
Cuándo usar:Deberíamos usar shared_ptr cuando queramos asignar un puntero sin formato a varios propietarios.
Para obtener más información y detalles sobre punteros inteligentes compartidos y otros, lea aquí .
Implementación definida por el usuario de punteros compartidos:
Programa:
CPP
#include <iostream>
using namespace std;
// Class representing a reference counter class
class Counter
{
public:
// Constructor
Counter()
: m_counter(0){};
Counter(const Counter&) = delete;
Counter& operator=(const Counter&) = delete;
// Destructor
~Counter() {}
void reset()
{
m_counter = 0;
}
unsigned int get()
{
return m_counter;
}
// Overload post/pre increment
void operator++()
{
m_counter++;
}
void operator++(int)
{
m_counter++;
}
// Overload post/pre decrement
void operator--()
{
m_counter--;
}
void operator--(int)
{
m_counter--;
}
// Overloading << operator
friend ostream& operator<<(ostream& os,
const Counter& counter)
{
os << "Counter Value : " << counter.m_counter
<< endl;
return os;
}
private:
unsigned int m_counter{};
};
// Class representing a shared pointer
template <typename T>
class Shared_ptr
{
public:
// Constructor
explicit Shared_ptr(T* ptr = nullptr)
{
m_ptr = ptr;
m_counter = new Counter();
if (ptr)
{
(*m_counter)++;
}
}
// Copy constructor
Shared_ptr(Shared_ptr<T>& sp)
{
m_ptr = sp.m_ptr;
m_counter = sp.m_counter;
(*m_counter)++;
}
// Reference count
unsigned int use_count()
{
return m_counter->get();
}
// Get the pointer
T* get()
{
return m_ptr;
}
// Overload * operator
T& operator*()
{
return *m_ptr;
}
// Overload -> operator
T* operator->()
{
return m_ptr;
}
// Destructor
~Shared_ptr()
{
(*m_counter)--;
if (m_counter->get() == 0)
{
delete m_counter;
delete m_ptr;
}
}
friend ostream& operator<<(ostream& os,
Shared_ptr<T>& sp)
{
os << "Address pointed : " << sp.get() << endl;
os << *(sp.m_counter) << endl;
return os;
}
private:
// Reference counter
Counter* m_counter;
// Shared pointer
T* m_ptr;
};
int main()
{
// ptr1 pointing to an integer.
Shared_ptr<int> ptr1(new int(151));
cout << "--- Shared pointers ptr1 ---\n";
*ptr1 = 100;
cout << " ptr1's value now: " << *ptr1 << endl;
cout << ptr1;
{
// ptr2 pointing to same integer
// which ptr1 is pointing to
// Shared pointer reference counter
// should have increased now to 2.
Shared_ptr<int> ptr2 = ptr1;
cout << "--- Shared pointers ptr1, ptr2 ---\n";
cout << ptr1;
cout << ptr2;
{
// ptr3 pointing to same integer
// which ptr1 and ptr2 are pointing to.
// Shared pointer reference counter
// should have increased now to 3.
Shared_ptr<int> ptr3(ptr2);
cout << "--- Shared pointers ptr1, ptr2, ptr3 "
"---\n";
cout << ptr1;
cout << ptr2;
cout << ptr3;
}
// ptr3 is out of scope.
// It would have been destructed.
// So shared pointer reference counter
// should have decreased now to 2.
cout << "--- Shared pointers ptr1, ptr2 ---\n";
cout << ptr1;
cout << ptr2;
}
// ptr2 is out of scope.
// It would have been destructed.
// So shared pointer reference counter
// should have decreased now to 1.
cout << "--- Shared pointers ptr1 ---\n";
cout << ptr1;
return 0;
}
--- Shared pointers ptr1 --- Address pointed : 0x1cbde70 Counter Value : 1 --- Shared pointers ptr1, ptr2 --- Address pointed : 0x1cbde70 Counter Value : 2 Address pointed : 0x1cbde70 Counter Value : 2 --- Shared pointers ptr1, ptr2, ptr3 --- Address pointed : 0x1cbde70 Counter Value : 3 Address pointed : 0x1cbde70 Counter Value : 3 Address pointed : 0x1cbde70 Counter Value : 3 --- Shared pointers ptr1, ptr2 --- Address pointed : 0x1cbde70 Counter Value : 2 Address pointed : 0x1cbde70 Counter Value : 2 --- Shared pointers ptr1 --- Address pointed : 0x1cbde70 Counter Value : 1
Publicación traducida automáticamente
Artículo escrito por mayank prasad y traducido por Barcelona Geeks. The original can be accessed here. Licence: CCBY-SA