CODEWITHSUNDEEP
c++memory-managementvectormemory-leaksdestructor
usesaar2310116
usesaar2310116

Reputation: 3

C++ Memory Leak using list class and push_back

C++ Memory Leak using list class and push_back

void EMAdd(int n)
{
   list<Employee*> em;
   for (int i = 1; i <= n; i++)
      em.push_back(new Employee());
}

Q1. at the end , the destructor of class list automatically deletes the nodes of em?

Q2. But why this function still has a memory leak?

Thanks, I would appreciate your answer!

Upvotes: 0

Views: 2362

Answers (2)

David G
David G

Reputation: 96835

You should have a list of unique_ptrs so that the memory will be freed upon destruction:

std::list<std::unique_ptr<Employee>> em;

But as David Brown said, you shouldn't be using pointers to begin with.

Upvotes: 2

David Brown
David Brown

Reputation: 13526

The destructor of Employee is not called. You have a list of pointers to Employee objects, not a list of Employee objects. When the list's destructor is called it will destroy the pointers to the Employee object, but not the objects they point to which you created with new Employee(). They will still be in memory but the only references to them are lost when the list is destroyed, leaking that memory.

Remember every call to new must have a matching call to delete somewhere. However, better yet don't use pointers at all and simply use a list of Employee objects directly. 

void EMAdd(int n)
{
   list<Employee> em;
   for (int i = 1; i <= n; i++)
      em.push_back(Employee());
}

Since each element in std::list is already dynamically allocated, a list of pointers is redundant and essentially gives you a set of pointers to pointers.

Upvotes: 6

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