[cdl-studenti] [OOP] Eliberare automata de memorie.

[Andrei Soare]

Se elibereaza, intr-adevar, dar dupa ce se copiaza in z. Se va apela apoi destructorul lui y si in final si pe cel al lui z si intr-adevar o sa faca free de 2 ori pe aceeasi zona de memorie.

Ca sa nu faca free de 2 ori pe aceeasi zona de memorie, trebuie neaparat implementat copy constructor si copy assignment operator sa aloce o zona noua de memorie pentru toate datele alocate dinamic din clasa.

Mereu cand o clasa are membri alocati dinamic trebuie implementat de mana copy constructor si copy assignment operator.

-----Original Message-----
From: marius Dragus

Eu am testat si se cam elibereaza. Se apeleaza destructorul pentru variabila
locala y.

2010/3/6 Dan-George Filimon <dangeorge.filimon at gmail.com>

> Nu se elibereaza y cand zici tu la pasul 2 din cate inteleg eu.
>
>
> On Mar 6, 2010, at 4:41 PM, marius Dragus wrote:
>
> Nu e ok. Varianta asta e gresita din mai multe motive (produce double free,
> copiaza memorie inexistenta).
>
> z= x+y;
>
> 0. Se apeleaza operatorul + pentru x
> 1. Se aloca y  in operator+.
> 2. Se apeleaza destructorul pentru y
> 3. Se apeleaza operatorul de asignare pentru z ( dar partea dreapta a fost
> eliberata deja la pasul 2 -- deci e gresit)
> 4. Se apelte ca fiecare obiect aloca dinamic un array, iar o operatie
>>> de genul x =a +b+c ar cauza memory leak-uri.
>>> >
>>> > Cum s-ar putea face asta?
>>> >
>>> > Mai jos este codul. Mentin un contor al constructorilor/destructorilor,
>>> si se vede evident ca se obtin memory leakuri.
>>> >
>>> > Mersi,
>>> > Marius
>>> >
>>> > /*************************CODE*********************/
>>> >
>>> > #include <iostream>
>>> >
>>> > int count = 0;
>>> > using namespace std;
>>> >
>>> > struct mine
>>> > {
>>> >     int * u;
>>> >     mine()
>>> >     {
>>> >     u = new int[10000];
>>> >     count++;
>>> >     }
>>> >
>>> >     ~mine()
>>> >     {
>>> >     delete[] u;
>>> >     count--;
>>> >     }
>>> >
>>> >     mine & operator=(const mine & x)
>>> >     {
>>> >     //cout << "assign" << endl;
>>> >     u = x.u;
>>> >     }
>>> >
>>> >
>>> > };
>>> >
>>> > mine& operator+(const mine & x, const mine &y)
>>> > {
>>> >     mine * ret = new mine;
>>> >     return *ret;
>>> > }
>>> >
>>> > int main()
>>> > {
>>> >
>>> >     mine a, b, c, d;
>>> >     mine e;
>>> >
>>> >
>>> >     for (int i = 0; i<10; i++)
>>> >     {
>>> >     e = a + b + c + d;
>>> >
>>> >     }
>>> >
>>> >     cout << count << "\n"; // afiseaza 35 desi ar trebui sa fie 5
>>> >
>>> >     return 0;
>>> > }
>>> >
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