Why is char** (or any T**) to void** cast invalid?

Question

In the first comment to Python C Module - Malloc fails in specific version of Python, @user694733 mentions that casting char** to void** is not val

Answer 1

If that was allowed, it would create a loop hole in the type system:

T* ptr;
void **vptr = &ptr; // &ptr is of type T**
int value;
*vptr = &value;     // &value is int*, can be converted to void*

At this point, ptr, which is according to the type system a pointer to T, is pointing to value that is an int. While the language allows you to circumvent the type system, you have to explicitly request it. Implicit conversions are designed to avoid this type of issues.