On 27/06/2019 13:52, Bagaskoro Kang wrote:

the creator apis have two out params: Interface** pointer and unsigned* size and the destroyer functions must be called with pointer and the size.

Interface** obj; unsigned size; int ret = Create(... ... ... &obj, &size);

and then we need to call a Release(obj, size) if the ret is success.

I do not think I can use the out_ptr with these APIs ???

I assume that's a typo and should be "Interface* obj". You wouldn't be able to use it out of the box with that interface, but if you define a custom smart pointer (which just wraps std::unique_ptr with a deleter that passes the size, for example) then you could probably get it to work. Spreading the responsibilities over two parameters does make things more tricky, though. If it's at all possible to remove the requirement to pass size around, you should do that instead. (It's not normally needed for array allocation, for example.)

also we call the Linux kernel C API posix_memalign() and we assign to unique_ptr. is not possible to use out_ptr with ?

std::unique_ptr upNumf; void * pNumf; int ret = posix_memalign(&pNumf, 64, nNumf); if (!ret) upNumf.reset((Numf*)pNumf);

Why not use std::aligned_storage or put alignas on the class instead?

Dear Bagaskoro Kang, I apologize, I thought my previous message got the example through to you, but it seems like it did not. Here is the example using out_ptr to do what you describe: struct SizedDeleter { size_t size = 0; void operator()(Interface* obj) const { DeleteBusInterface(obj, size); } }; using bop = boost::out_ptr; size_t& size_ref = p_obj.get_deleter().size; std::unique_ptr obj;int ret = CreateBusInterface(..., bop::out_ptr(obj), &size_ref);if (ret != 0) { throw std::runtime_error("deep sadness"); }/* use obj ...*/ Similarly, for posix_memalign: using bop = boost::out_ptr; std::unique_ptr upNumf;/* some work... */int ret = posix_memalign(bop::out_ptr(upNumf), 64, nNumf);if (ret != 0) { throw std::runtime_error("something went wrong and posix_memalign failed!"); } I hope that helps. Sincerely, JeanHeyd

On Wed, Jun 26, 2019, 11:12 PM JeanHeyd Meneide via Boost < boost@lists.boost.org> wrote:

On Wed, Jun 26, 2019 at 11:05 PM Gavin Lambert via Boost < boost@lists.boost.org> wrote:

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On 27/06/2019 13:52, Bagaskoro Kang wrote:

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the creator apis have two out params: Interface** pointer and unsigned* size and the destroyer functions must be called with pointer and the size.

Interface** obj; unsigned size; int ret = Create(... ... ... &obj, &size);

and then we need to call a Release(obj, size) if the ret is success.

I do not think I can use the out_ptr with these APIs ???

struct sized_deleter { unsigned size; ... };

using bop = boost::out_ptr;

std::unique_ptr p_obj; int ret = Create(..., bop::out_ptr(p_obj), &p_obj.get_deleter().size) if (LIBNAME_HAS_FAILED(ret)) { throw std::runtime_error("deep sadness"); }

This example is less pretty because I'm putting the size in the deleter, but it works.

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also we call the Linux kernel C API posix_memalign() and we assign to unique_ptr. is not possible to use out_ptr with ?

std::unique_ptr upNumf; void * pNumf; int ret = posix_memalign(&pNumf, 64, nNumf); if (!ret) upNumf.reset((Numf*)pNumf);

using bop = boost::out_ptr;

std::unique_ptr upNumf; int ret = posix_memalign(bop::out_ptr(upNumf), 64, nNumf); if (ret != 0) { throw std::runtime_error("something went wrong, but at least we're not leaking memory here."); }

Casting support is built in to the API: you can go from strongly typed pointers to void**, or other related pointers by passing the type as a template argument.

These seem like they would make good examples for the docs. Zach