Set shared_ptr with new_pointer that is old_pointer + offset

Yes this is possible. You can use constructor 8, the aliasing constructor from this reference: https://en.cppreference.com/w/cpp/memory/shared_ptr/shared_ptr

// make sure you use an array deleter std::shared_ptr<char> osp(new char[1024], std::default_delete<char[]>()); // load the data into your buffer at osp.get() // Find the offset in the data by parsing auto const offset = parse_buffer_for_offset(osp.get()); // Now set a new offset into the data std::shared_ptr<char> nsp(osp, osp.get() + offset); 

Now nsp.get() returns the offset address but the original array will get deleted properly.

Note: The offset is a property of each shared_ptr so if you copy the shared_ptr nsp you get another shared_ptr with the same offset. This works whether you construct a new copy or assign a copy to an existing shared_ptr.

This means you can have different shared_ptr with different offsets that all manage the same, underlying resource which will only be cleaned up after all shared_ptr are destroyed.

To see this in operation consider the following code:

std::shared_ptr<char> original_sp(new char[1024], std::default_delete<char[]>()); std::shared_ptr<char> offset_100_sp1(original_sp, original_sp.get() + 100); std::shared_ptr<char> offset_100_sp2 = offset_100_sp1; std::shared_ptr<char> offset_200_sp1(original_sp, original_sp.get() + 200); std::shared_ptr<char> offset_200_sp2 = offset_200_sp1; std::cout << "\nPointers managing the array: " << original_sp.use_count() << '\n'; std::cout << "\nOffset 100 pointers:" << '\n'; std::cout << std::distance(original_sp.get(), offset_100_sp1.get()) << '\n'; std::cout << std::distance(original_sp.get(), offset_100_sp2.get()) << '\n'; std::cout << "\nOffset 200 pointers:" << '\n'; std::cout << std::distance(original_sp.get(), offset_200_sp1.get()) << '\n'; std::cout << std::distance(original_sp.get(), offset_200_sp2.get()) << '\n'; 

Output:

Pointers managing the array: 5 Offset 100 pointers: 100 100 Offset 200 pointers: 200 200