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shared_ptr i C++

std::delt_ptr er en af ​​de smarte pointer introduceret i C++11. I modsætning til en simpel pointer har den en tilknyttet kontrolblok, der holder styr på referenceantallet for det administrerede objekt. Dette referenceantal deles mellem alle kopierne af shared_ptr-forekomsterne, der peger på det samme objekt, hvilket sikrer korrekt hukommelsesstyring og sletning.

Forudsætninger: Pointere i C++ , Smarte pointere i C++ .



shared_ptr-in-CPP

Delt pointer i C++

Syntaks for std::shared_ptr

Shared_ptr af type T kan erklæres som:

  std::shared_ptr      ptr_name;>

Initialisering af shared_ptr-objekter

Vi kan initialisere shared_ptr ved hjælp af følgende metoder:



1. Initialisering ved hjælp af en ny pointer 

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

2. Initialisering ved hjælp af eksisterende Pointer 

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

Medlem Metoder til shared_ptr

Følgende er nogle medlemmer forbundet med shared_ptr:



Metode Beskrivelse
Nulstil() Nulstiller std::shared_ptr til tom, og frigiver ejerskabet af det administrerede objekt.
use_count() Returnerer det aktuelle referenceantal, der angiver, hvor mange std::shared_ptr-forekomster, der deler ejerskab.
enestående() Tjek, om der kun er én std::shared_ptr, der ejer objektet (referenceantal er 1).
få() Returnerer en rå pointer til det administrerede objekt. Vær forsigtig, når du bruger denne metode.
swap(shr_ptr2) bytter indholdet (ejerskabet) af to std::shared_ptr-forekomster.

Eksempler på std::shared_ptr

Eksempel 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->vis();> > >// creating a new shared pointer that shares ownership> >shared_ptr> p2(p1);> >p2->vis();> > >// 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;> }> 

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Produktion 

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

Eksempel 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();> }> 

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Produktion 

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.>

Eksempel 3: Implementering af en linket liste ved hjælp af 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->næste) {> >current = current->næste;> >}> >current->næste = 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->næste;> >return>;> >}> >shared_ptr current = head;> >while> (current->næste> >&& current->næste->data != val) {> >current = current->næste;> >}> >if> (current->næste && aktuel->næste->data == val) {> >current->næste = nuværende->næste->næste;> >}> >}> >// Traverse and print the linked list> >void> Print()> >{> >shared_ptr current = head;> >while> (current) {> >cout current = current->Næste; } 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; }> 

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python ny linje 

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Produktion 

Linked List: 1 ->2 -> 3 -> NULL Linked List efter sletning 2: 1 -> 3 -> NULL>