c++ - Casting to void* and Back to Original_Data_Type*

Question

I have seen and used this many times is C++, specially in various thread implementations. What I wonder is if there are any pitfalls/ issues of doing this? Is there any way that we could run in to an error or undefined condition when we are casting to void* and back again? How should we resolve such issues if there are any?

Thank you.

Answer 1

This is perfectly valid. Here is what standard has to say about it:

§4.10 Pointer conversions

2 An rvalue of type "pointer to cv T," where T is an object type, can be converted to an rvalue of type "pointer to cv void." The result of converting a "pointer to cv T" to a "pointer to cv void" points to the start of the storage location where the object of type T resides, as if the object is a most derived object (1.8) of type T (that is, not a base class subobject).

which means you can convert your pointer to class to a void pointer. And ...

§5.2.9 Static cast

10 An rvalue of type "pointer to cv void" can be explicitly converted to a pointer to object type. A value of type pointer to object converted to "pointer to cv void" and back to the original pointer type will have its original value.

which means you can use static_cast to convert a void pointer back to an original class pointer.

Hope it helps. Good Luck!