C++ mechanism of constructing, deconstructing and pointer to class object -

C++ mechanism of constructing, deconstructing and pointer to class object -

#include <iostream> using namespace std; class { private: int m_i; friend int main(int argc, char const *argv[]); public: (int = 0):m_i(i){}; void display() { cout << m_i << endl; } int result() {return m_i;} }; void createa(a *pa) { pa = new a(1); } a* createa() { a(2); homecoming &a; } void createaonstack() { a(3); } int main(int argc, char const *argv[]) { a; * pa = &a; pa->display(); createa(pa); pa->display(); * a2 = createa(); cout << a2->m_i << endl; createaonstack(); cout << a2->m_i << endl; homecoming 0; }

the results of programme above is

0 0 2 3

how explain result 2 , 3? understanding, object created in function createa() should deconstructed, , pointer returns should point null, why a2->m_i can 2. , 3 more confusing, seems function createaonstack() has nil a2.

you said

from understanding, object created in function createa() should deconstructed, , pointer returns should point null, why a2->m_i can 2.

it true

the object created in function createa() should deconstructed

it not true that

and pointer returns should point null

the pointer returned createa non-null though invalid pointer utilize in calling function.

but why a2->m_i can 2.

it's pure coincidence. undefined behavior. can happen when dereference a2.

c++