Question

This is kind of basic but I can’t seem to get a hold on this one. Reference here

Are void *p and const void *p sufficiently different? Why would a function use const void * instead of void *?

Answer 1

The reason to use void* at all (whether const or not) is the kind of genericity it provides. It’s like a base class: All pointers are void* and can implicitly cast into it, but casts from void* to typed pointers have to be done explicitly and manually.

Usually, C++ has better ways to offer to do this (namely OO and templates), so it doesn’t make much sense to use void* at all, except when you’re interfacing C. However, if you use it, then const offers just what it offers elsewhere: you need an (additional) const_cast to be able to change the object referred to, so you are less likely to change it accidentally.

Of course, this relies on you not employing C-style casts, but explicit C++ casts. The cast from void* to any T* requires a static_cast, and this doesn’t allow removing of const. So you can cast const void* to const char* using static_cast, but not to char*. This would need an additional const_cast.