File Stream change its address during writing text contents to the stream

Hi guys,

I wrote a program to write text contents to file stream through fputs, the file stream address was changed
in the middle of writing text content to the stream (11% text content have been put into the file stream),
that cause the file stream pointer can be evaluated problem and raise exception on stream validation code in fputs library function, my question is what things could go wrong to make file stream pointer changed its address to something else or a NULL pointer if the file stream have not been flushed and closed.

Thanks

Jason