Question

I’m tryin to use a custom container, and in that container’s constructor i pass a memory pool allocator.
The whole thing starts like this:

AllocatorFactory alloc_fac;

//Creates a CPool allocator instance with the size of the Object class
IAllocator* object_alloc = alloc_fac.GetAllocator<CPool>(1000,sizeof(Object));
//Creates a CPool allocator instance with the size of the BList<Object> class
IAllocator* list_alloc = alloc_fac.GetAllocator<CPool>(10,sizeof(BList<Object>));
//Same logic in here as well
IAllocator* node_alloc = alloc_fac.GetAllocator<CPool>(1000,sizeof(BListNode<Object>));

The IAllocator class looks like this:

 class IAllocator
{

public:

    virtual void* allocate( size_t bytes ) = 0;
    virtual void deallocate( void* ptr ) = 0;

    template <typename T>
    T* make_new()
    { return new ( allocate( sizeof(T) ) ) T (); }

    template <typename T, typename Arg0>
    T* make_new( Arg0& arg0 )
    { return new ( allocate( sizeof(T) ) ) T ( arg0 ); }

            .......
}

And the container class’s constructor looks like this:

template <class T>
class BList {
......
public:
/**
 *@brief Constructor
 */
BList(Allocators::IAllocator& alloc){
     _alloc = alloc;
    reset();
    }
/**
 *@brief Constructor
 *@param inOther the original list
 */
 BList(const BList<T>& inOther){
    reset();
    append(inOther);
    }
.....
}

And when I do this:

 BList<Object> *list = list_alloc->make_new<BList<Object>>(node_alloc);

The compiler complains about this:

Error 1 error C2664: ‘Containers::BList::BList(Allocators::IAllocator &)’ : cannot convert parameter 1 from ‘Allocators::IAllocator *’ to ‘Allocators::IAllocator &’ c:\licenta\licenta-transfer_ro-02may-430722\licenta\framework\framework\iallocator.h 21 Framework

I think i went over my head with this one….

Answer 1

The existing answers are correct, but a quick note on how to read the error yourself: you just have to split it into pieces …

Error 1 error C2664: 'Containers::BList::BList(Allocators::IAllocator &)' : cannot convert parameter 1 from 'Allocators::IAllocator *' to 'Allocators::IAllocator &'

reads:

• you’re calling Containers::BList::BList(Allocators::IAllocator &), which is a constructor taking one argument, a reference to an IAllocator
• cannot convert parameter 1 means the compiler is having trouble with the type of that first (and only) argument
  • you’ve given it this type: ... from 'Allocators::IAllocator *'
  • and it wanted this type (to match the constructor declaration): ... to 'Allocators::IAllocator &'

so, how do you convert from the pointer you have to the reference the constructor wants?

---

OK, I’ve added the actual answer as well:

Allocators::IAllocator *node_alloc = // ...
Allocators::IAllocator &node_alloc_ref = *node_alloc;
BList<Object> *list = list_alloc->make_new<BList<Object>>(node_alloc_ref);

or just:

BList<Object> *list = list_alloc->make_new<BList<Object>>(*node_alloc);