logo

TechCodeview

shared_ptr v C++

std::shared_ptr je eden od pametnih kazalcev, predstavljenih v C++11. Za razliko od preprostega kazalca ima povezan kontrolni blok, ki spremlja štetje referenc za upravljani objekt. To število sklicev je v skupni rabi med vsemi kopijami primerkov shared_ptr, ki kažejo na isti objekt, kar zagotavlja pravilno upravljanje pomnilnika in brisanje.

Predpogoji: Kazalci v C++ , Pametni kazalci v C++ .



skupni_ptr-v-CPP

Skupni kazalec v C++

Sintaksa std::shared_ptr

Shared_ptr tipa T je mogoče deklarirati kot:

  std::shared_ptr      ptr_name;>

Inicializacija objektov shared_ptr

Shared_ptr lahko inicializiramo z naslednjimi metodami:



1. Inicializacija z uporabo novega kazalca 

shared_ptr ptr (new T()); shared_ptr ptr = make_shared (new T());>

2. Inicializacija z uporabo obstoječega kazalca 

shared_ptr ptr(already_existing_pointer); shared_ptr ptr = make_shared(already_existing_pointer);>

Metode članov za shared_ptr

Sledi nekaj članov, povezanih s shared_ptr:



Metoda Opis
ponastaviti() Ponastavi std::shared_ptr na prazno in sprosti lastništvo nad upravljanim objektom.
use_count() Vrne trenutno število referenc, ki kaže, koliko primerkov std::shared_ptr si deli lastništvo.
edinstven() Preverite, ali je samo en std::shared_ptr lastnik objekta (število referenc je 1).
dobiti () Vrne neobdelani kazalec na upravljani objekt. Pri uporabi te metode bodite previdni.
zamenjava (shr_ptr2) zamenja vsebino (lastništvo) dveh primerkov std::shared_ptr.

Primeri std::shared_ptr

Primer 1:

C++




// C++ program to demonstrate shared_ptr> #include> #include> using> namespace> std;> class> A {> public>:> >void> show() { cout << 'A::show()' << endl; }> };> int> main()> {> >// creating a shared pointer and accessing the object> >shared_ptr p1(> new> A);> >// printting the address of the managed object> >cout << p1.get() << endl;> >p1->pokaži();> > >// creating a new shared pointer that shares ownership> >shared_ptr> p2(p1);> >p2->pokaži();> > >// 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;> }> 

>

>

Izhod 

0x1365c20 A::show() A::show() 0x1365c20 0x1365c20 2 2 0 1 0x1365c20>

Primer 2:

C++




// C++ program to illustrate the use of make_shared> #include> #include> 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();> }> 

>

>

Izhod 

Value 1: 42 Value 2: 24 shared pointer 1 and shared pointer 3 point to the same object. Value 2 (after swap): 42 Value 3 (after swap): 24 Both shared pointer 1 and shared pointer 2 are valid.>

Primer 3: Implementacija povezanega seznama z uporabo std::shared_ptr

C++




#include> #include> using> namespace> std;> // Define a singly linked list node> struct> Node {> >int> data;> >shared_ptr 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 newNode = make_shared(val);> >if> (!head) {> >head = newNode;> >}> >else> {> >shared_ptr current = head;> >while> (current->naslednji) {> >current = current->naslednji;> >}> >current->naslednji = novo vozlišče;> >}> >}> >// Delete a node with a given value from the linked list> >void> del(>int> val)> >{> >if> (!head) {> >return>;> >}> >if> (head->podatki == val) {> >head = head->naslednji;> >return>;> >}> >shared_ptr current = head;> >while> (current->naslednji> >&& current->naslednji->podatki != val) {> >current = current->naslednji;> >}> >if> (current->naslednji && trenutni->naslednji->podatki == val) {> >current->naslednji = trenutno->naslednji->naslednji;> >}> >}> >// Traverse and print the linked list> >void> Print()> >{> >shared_ptr current = head;> >while> (current) {> >cout current = current->Naslednji; } cout<< 'NULL' << endl; } private: shared_ptr 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; }> 

>

java naključna matematika naključna 

>

Izhod 

Linked List: 1 ->2 -> 3 -> NULL Povezani seznam po brisanju 2: 1 -> 3 -> NULL>>