C++ Still Bites Back
I don’t know how many times I’ve thought to myself that I knew it all. Many times I’ve coded something that I was absolutely sure was correct only to find out I was drastically wrong.
What’s wrong with this code?
class Object
{
public:
Object()
: m_pdata( new BYTE[100] )
{
}
~Object()
{
delete[] m_pdata;
}
private:
BYTE *m_pdata;
};
class Interface
{
public:
static Object* AllocateObject() { return new Object(); }
static void DeleteObject( void* pObject )
{ delete pObject; }
};
...
void Function()
{
Object* pObject = Interface::AllocateObject();
// do something
Interface::DeleteObject( pObject );
}
Answer
It will leak memory. DeleteObject takes in a void* which when deleted will not call the destructor for the Object class and m_pdata leaks.
I made this mistake when I added a new type of object that needed to be allocated from an interface. Then I tried to consolidate the “Delete” functions into a single one (read: "make better"). I didn’t see it when I coded because the classes I tested it with had trivial destructors and freeing the memory was enough. It wasn’t until testers tried more complicated scenarios did the bug manifest itself (read: "made totally worse").
