V554. Incorrect use of smart pointer

31.03.2011

Analyzer located an issue then the usage of smart pointer could lead to undefined behavior, in particular to the heap damage, abnormal program termination or incomplete objects destruction. The error here is that different methods will be used to allocate and free memory.

Consider a sample:

void Foo()
{
  struct A
  {
    A() { cout << "A()" << endl; }
    ~A() { cout << "~A()" << endl; }
  };

  std::unique_ptr<A> p(new A[3]);
}

By default, the unique_ptr class uses the 'delete' operator to release memory. That is why only one object of the 'A' class will be destroyed and the following text will be displayed:

A()
A()
A()
~A()

To fix this error, we must specify that the class must use the 'delete []' operator. Here is the correct code:

std::unique_ptr<A[]> p(new A[3]);

Now the same number of constructors and destructors will be called and we will see this text:

A()
A()
A()
~A()
~A()
~A()

Consider another sample:

std::unique_ptr<int []> p((int *)malloc(sizeof(int) * 5));

The function 'malloc()' is used to allocate memory while the 'delete []' operator is used to release it. It is incorrect and we must specify that the 'free()' function must be used to release memory. This is the correct code:

int *d =(int *)std::malloc(sizeof(int) * 5);
unique_ptr<int, void (*)(void*)> p(d, std::free);

Additional materials on this topic:

You can look at examples of errors from real projects which were detected by this diagnostic message.