What is guaranteed about the size of a function pointer?

Question

In C, I need to know the size of a struct, which has function pointers in it. Can I be guaranteed that on all platforms and architectures:

• the size of a void*

Answer 1

There is a practical example of differing sizes that used to be common. In the MS-DOS & early Windows C programming, in the "medium" memory model you had 16-bit data pointers but 32-bit function pointers, and the "compact" memory model was the other way round.