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I was given an API for some library (nng to be exact) it has a C-like interface for allocating and deallocating a message object:

int nng_msg_alloc(nng_msg **, size_t);
void nng_msg_free(nng_msg *);

I'm trying to create a C++ interface for the library. I would like to create a shared_ptr of a nng_msg object, but I'm struggling with the implementation. How do i pass the allocator and deallocator to the shared object?

user17732522
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Omer Kawaz
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    maybe this you're looking for https://stackoverflow.com/questions/41748542/shared-ptr-custom-allocator-together-with-custom-deleter – Ferenc Deak Mar 07 '22 at 09:01
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    You probably don't want a custom allocator, just create a `shared_ptr` from the pointer returned by `nng_msg_alloc`. Then the deleter is pretty straight forward. – super Mar 07 '22 at 09:04

1 Answers1

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You only have to pass the allocated pointer and the custom deleter to std::shared_ptr, for example:

std::shared_ptr<nng_msg> new_nng_msg(std::size_t size) {
    nng_msg* ptr;
    auto res = nng_msg_alloc(&ptr, size);

    // example error handling, adjust as appropriate
    if(res != 0)
        throw std::bad_alloc{};

    return {ptr, nng_msg_free};
}
user17732522
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