C++ shared_ptr用法及代碼示例

// C++ program to demonstrate shared_ptr
#include <iostream>
#include <memory>
using namespace std;
class A {
public:
    void show() { cout << "A::show()" << endl; }
};
int main()
{
    // creating a shared pointer and accessing the object
    shared_ptr<A> p1(new A);
    // printting the address of the managed object
    cout << p1.get() << endl;
    p1->show();
   
    // creating a new shared pointer that shares ownership
    shared_ptr<A> p2(p1);
    p2->show();
   
    // printing addresses of P1 and P2
    cout << p1.get() << endl;
    cout << p2.get() << endl;
   
    // Returns the number of shared_ptr objects
    // referring to the same managed object.
    cout << p1.use_count() << endl;
    cout << p2.use_count() << endl;
   
    // Relinquishes ownership of p1 on the object
    // and pointer becomes NULL
    p1.reset();
    cout << p1.get() << endl;
    cout << p2.use_count() << endl;
    cout << p2.get() << endl;
    /*
    These lines demonstrate that p1 no longer manages an
    object (get() returns nullptr), but p2 still manages the
    same object, so its reference count is 1.
        */
    return 0;
}

// C++ program to illustrate the use of make_shared
#include <iostream>
#include <memory>
using namespace std;
int main()
{
    // Creating shared pointers using std::make_shared
    shared_ptr<int> shr_ptr1 = make_shared<int>(42);
    shared_ptr<int> shr_ptr2 = make_shared<int>(24);
    // Accessing the values using the dereference operator
    // (*)
    cout << "Value 1: " << *shr_ptr1 << endl;
    cout << "Value 2: " << *shr_ptr2 << endl;
    // Using the assignment operator (=) to share ownership
    shared_ptr<int> shr_ptr3 = shr_ptr1;
    // Checking if shared pointer 1 and shared pointer 3
    // point to the same object
    if (shr_ptr1 == shr_ptr3) {
        cout << "shared pointer 1 and shared pointer 3 "
                "point to the same object."
             << endl;
    }
    // Swapping the contents of shared pointer 2 and shared
    // pointer 3
    shr_ptr2.swap(shr_ptr3);
    // Checking the values after the swap
    cout << "Value 2 (after swap): " << *shr_ptr2 << endl;
    cout << "Value 3 (after swap): " << *shr_ptr3 << endl;
    // Using logical operators to check if shared pointers
    // are valid
    if (shr_ptr1 && shr_ptr2) {
        cout << "Both shared pointer 1 and shared pointer "
                "2 are valid."
             << endl;
    }
    // Resetting a shared pointer
    shr_ptr1.reset();
}

#include <iostream>
#include <memory>
using namespace std;
// Define a singly linked list node
struct Node {
    int data;
    shared_ptr<Node> next;
    Node(int val)
        : data(val)
        , next(NULL)
    {
    }
};
class LinkedList {
public:
    LinkedList()
        : head(NULL)
    {
    }
    // Insert a new node at the end of the linked list
    void insert(int val)
    {
        shared_ptr<Node> newNode = make_shared<Node>(val);
        if (!head) {
            head = newNode;
        }
        else {
            shared_ptr<Node> current = head;
            while (current->next) {
                current = current->next;
            }
            current->next = newNode;
        }
    }
    // Delete a node with a given value from the linked list
    void del(int val)
    {
        if (!head) {
            return;
        }
        if (head->data == val) {
            head = head->next;
            return;
        }
        shared_ptr<Node> current = head;
        while (current->next
               && current->next->data != val) {
            current = current->next;
        }
        if (current->next && current->next->data == val) {
            current->next = current->next->next;
        }
    }
    // Traverse and print the linked list
    void Print()
    {
        shared_ptr<Node> current = head;
        while (current) {
            cout << current->data << " -> ";
            current = current->next;
        }
        cout << "NULL" << endl;
    }
private:
    shared_ptr<Node> head;
};
int main()
{
    LinkedList linkedList;
    // Insert nodes into the linked list
    linkedList.insert(1);
    linkedList.insert(2);
    linkedList.insert(3);
    // Print the linked list
    cout << "Linked List: ";
    linkedList.Print();
    // Delete a node and print the updated linked list
    linkedList.del(2);
    cout << "Linked List after deleting 2: ";
    linkedList.Print();
    return 0;
}