But code outside the standard library can’t do that, can it? fopen returns a pointer to a FILE, and you can’t know how a struct FILE should be copied. You can’

But code outside the standard library can’t do that, can it? fopen returns a pointer to a FILE, and you can’t know how a struct FILE should be copied. You can’t just memcpy the bits and then mix calls to fread using pointers to the old and the new FILE struct, for example. I think the standard library need not even support calls using a pointer to a FILE struct it didn’t create.