advice on how to free memory leak

[chuchi]

Hi everyone!


I have to deal with a memory leak in a code that is not mine, and I want to ask for advice on what is an elegant way to free the memory leak. The code looks like this:






#include <iostream>
#include <vector>
using namespace std;


class A
{
public:


int a;


A(int a_) : a(a_)
{}
};


class B
{
public:


B(A * a) : a_(a)
{
}
private:
A *a_;


};


class Example
{
public:


void createElements(int count)
{
vectorB.clear();
for (int i = 0; i < count; i++)
{
A * a = new A(i);
B b(a);
vectorB.push_back(b);
}
}


private:
std::vector <B> vectorB;
};




int main()
{
Example example;
example.createElements(3);
}













The memory leak comes from the line :




A * a = new A(i);



I thought that maybe I could maintain a vector<A*> and add the objects to this vector. Then, when deleting Example (or when calling createElements again) I would iterate through that vector, free its elements and clear the vector.


What do you think about this approach?


Thanks a lot!

[norobro]

... advice on what is an elegant way to free the memory leak. ...Use std::shared_ptr http://en.cppreference.com/w/cpp/memory/shared_ptr
Like this:
//A * a = new A(i);
std::shared_ptr<A> a(new A(i));


You'll need to make changes in class B also.

[chuchi]

Hi norobro, thank you for your response!




If I use a shared pointer, once the method is done all the pointers are freed, and I need to maintain such pointers for later use. This is an example :




#include <iostream>
#include <vector>
#include <memory>
using namespace std;


class A
{
public:


int a;


A(int a_) : a(a_)
{
}
};


class B
{
public:


A *a_;


B(A * a) : a_(a)
{
}
};


class Example
{
public:


void createElements(int count)
{
vectorB.clear();
for (int i = 0; i < count; i++)
{
//A * a = new A(i);
std::shared_ptr<A> a(new A(i));
B b(a.get());
vectorB.push_back(b);
}
}


void printElements()
{
for (int i = 0; i < vectorB.size(); i++)
{
printf("value = %d\n", vectorB[i].a_->a);
}
}


private:
std::vector <B> vectorB;
};


int main()
{
Example example;
example.createElements(3);
example.printElements();
}



Besides, I can't make changes in class B, because there is another client code which uses this class in this way :






A *a = new A;


B b(a);
//do some stuff with b
delete a;







So I can not delete a_ within B destructor...

[dwhitney67]

Besides, I can't make changes in class B, because there is another client code which uses this class in this way :


You can't make changes, or you just don't want to??? Are the coding police preventing you from making code changes?

My advice is to use a shared pointer (per the advice that was given to you earlier), or redesign your project in a different way. If you do not want to use a shared pointer, then class B should own the A object, and should be responsible for deleting it. The client code that you supposedly can't change should be changed. It is that simple.

[james222]

Shared pointer will be the best approach in this case.