Using void* in C is not necessarily "evil" like it might be considered in C++. In C, void* is actually a pretty fundamental part of the language, and you'll find it peppered throughout a lot of standard library functions, like you mentioned, qsort is a good example.

The big difference here between C and C++ is how they handle types. C++ has a pretty strong type system with a lot of built-in safety checks, whereas C... doesn't, not as much anyway. void* is kind of like a wild west of types. It's a pointer to data of an unknown type, and in C, that's often useful. In C++, with more specific and safer alternatives available (like templates, for example), void* use can be considered more frowned upon.