How to delete whole object by knowing only its base-pointer [duplicate] - c++

Question

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When to use virtual destructors?
(20 answers)
Closed 5 years ago.
I'm trying to implement autorelease pool in c++, and have trouble with deallocating.
So we have root-class object:
class object {
public:
object() {
retainCount_ = 0;
}
~object() {
std::cout << "object " << Description() << " is dealocated" << std::endl;
}
/* code with retain/release here */
int retainCount() {
return retainCount_;
}
std::string Description() {
std::stringstream ss;
ss << this;
return ss.str();
}
private:
int retainCount_;
};
And some realization:
class Integer : public object {
public:
int i;
Integer(int ii) : i(ii) {}
~Integer() {
std::cout << "Integer " << Description() << " is dealocated" << std::endl;
}
};
And of course release pool class, which works with root-class pointers:
class release_pool {
public:
void insert(object* obj) {
pointers_.insert(obj);
}
void flush() {
std::set<object*>::iterator it = pointers_.begin();
std::set<object*>::iterator tmp;
const int N = pointers_.size();
for (int i = 0; i < N; i++) {
tmp = it;
it++;
if ((*tmp)->retainCount() == 0 ) {
object* obj = *tmp;
std::cout << "delete obj: " << obj->Description() << std::endl;
pointers_.erase(tmp);
delete obj;
}
}
}
private:
std::set<object*> pointers_;
};
main.cpp code for test:
int main () {
release_pool pool;
Integer* obj = new Integer(5);
pool.insert(obj);
std::cout << "before flush: " << obj->i << "\n";
pool.flush();
std::cout << "after flush: " << obj->i << "\n";
return 0;
}
After build, I get next:
before flush: 5
delete obj: 0x7f9a84c025d0
object 0x7f9a84c025d0 is dealocated
after flush: 5
At the end: destructor of root-class is invoked, but of Integer not. Hence, we have leaked memory, which is allocated for Integer object. Have you any ideas to fix it? How i can delete whole object, not root-part of it.

Answer 1

You need to make your object destructor virtual.