有没有办法将共享 ptr 转换为 void 指针，然后将 void 指针转换回共享指针？

Question

I have a shared pointer of objects throughout my application. Here is one example:

std::shared_ptr<MyTexture> texture = loadImageFromFile("someFile.png");

I am using a UI library called ImGui and this library has a concept of a texture ID, which is a void pointer. I am currently passing the data to this library by doing the following:

ImGui::Image(texture.get());

And my backend stores these textures in a map that points to the Graphics API related data type (it is a Vulkan descriptor set but ) to be able to render the texture. Now, I have one particular issue about this. I want to manage this with a smart pointer. However, I am passing it as a raw pointer; so, I am not able to just wrap it in a shared pointer because the original shared pointer will be destroyed by this. Internally, I am using shared pointers everywhere except for this one particular case. Is there some way that I can pass a shared pointer object itself as raw void pointer and then cast it back to shared pointer; so, I do not lose the shared pointer counter when passing the pointer to this function?

Answer 1

No , not with std::shared_ptr , I mean, you can get raw-pointer from smart-pointer, but you simply can't get SAME-INSTANCE of smart-pointer from raw-pointer.

But you can:

• Simply ensure your " void * " usage NEVER outlives the smart-pointer (else expect undefined-behaviour).
• Or implement your own smart-pointer class, which has internal hash-map, that stores instances as value and (with raw-pointer as key), then later in a method finds and returns smart-pointer by " void * " input (like: static MySmartPtr fromRaw(void *) ).
• Or manually store std::shared_ptr in a hash-map (like above but without custom smart-pointer implemention).