I am trying to use std::unique_ptr<T[]>
with custom memory allocators. Basically, I have custom allocators that are subclasses of IAllocator
, which provides the following methods:
void* Alloc( size_t size )
template<typename T> T* AllocArray( size_t count )
void Free( void* mem )
template<typename T> void FreeArray( T* arr, size_t count )
Since the underlying memory might come from a pre-allocated block, I need the special ...Array()
-methods to allocate and free arrays, they allocate/free memory and call T()
/ ~T()
on every element in the range. Now, as far as I know, custom deleters for std::unique_ptr
use the signature:
void operator()(T* ptr) const
In the case of unique_ptr<T[]>
, normally you would call delete[]
and be done with it, but I have to call FreeArray<T>
, for which I need the number of elements in the range. Given only the raw pointer, I think there is no way of obtaining the size of the range, hence the only thing I could come up with is this:
std::unique_ptr<T[], MyArrDeleter> somePtr( allocator.AllocArray<T>( 20 ), MyArrDeleter( allocator, 20 ) );
Where essentially the size of the array has to be passed into the deleter object manually. Is there a better way to do this? This seems quite error-prone to me...
Yes, there most certainly is a better way:
Use a maker-function.
template<class T, class A> std::unique_ptr<T[], MyArrDeleter>
my_maker(size_t count, A&& allocator) {
return {somePtr(allocator.AllocArray<T>(count), MyArrDeleter(allocator, count)};
}
auto p = my_maker<T>(42, allocator);
T*
doesn't contain such information, neither unique_ptr knows about the size of the array (since it uses directly a delete []
as you stated). You could let the T
be a unique_ptr<T>
to manage the destruction automatically but this could not be possible if the whole contiguous T*
is managed by a memory allocator (and not a single T*
object). Eg:
unique_ptr<unique_ptr<Foo>[]> data;
data.reset(new unique_ptr<Foo>[50]);
data[0].reset(new Foo());
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.