Are there practical uses for dynamic-casting to void pointer?

Casting pointers to void* has its importance since way back in C days. Most suitable place is inside the memory manager of Operating System. It has to store all the pointer and the object of what you create. By storing it in void* they generalize it to store any object on to the memory manager data structure which could be heap/B+Tree or simple arraylist.

For simplicity take example of creating a list of generic items(List contains items of completely different classes). That would be possible only using void*.

standard says that dynamic_cast should return null for illegal type casting and standard also guarantees that any pointer should be able to type cast it to void* and back from it with only exception of function pointers.

Normal application level practical usage is very less for void* typecasting but it is used extensively in low level/embedded systems.

Normally you would want to use reinterpret_cast for low level stuff, like in 8086 it is used to offset pointer of same base to get the address but not restricted to this.

Edit: Standard says that you can convert any pointer to void* even with dynamic_cast<> but it no where states that you can not convert the void* back to the object.

For most usage, its a one way street but there are some unavoidable usage.

It just says that dynamic_cast<> needs type information for converting it back to the requested type.

There are many API's that require you to pass void* to some object eg. java/Jni Code passes the object as void*.
Without type info you cannot do the casting.If you are confident enough that type requested is correct you can ask compiler to do the dynmaic_cast<> with a trick.

Look at this code: