I wonder if this is technically a bug. The stream is not opened for reading and yet you do an fread. I quickly glanced through the
C-Standard and I did not find an _explicit_ paragraph that this is
undefined behavior, but personally I'd expect it to be.

Regarding the last C example. Also here, you do not open using "w+".
Now, even if you used "w+", by the standard you'd have to do an fflush,
fseek, fsetpos or rewind before reading. I don't see a libc bug.