Availability:built-in
- Unix
 - If the system provides ioctl calls for this, these are used and tty_size/2 
properly reflects the actual size after a user resize of the window. The ioctl 
is issued on teh file descriptor associated with the 
user_inputstream. As a fallback, the system uses tty_get_capability/3 usingliandcocapabilities. In this case the reported size reflects the size at the first call and is not updated after a user-initiated resize of the terminal. - Windows
 - Getting the size of the terminal is provided for swipl-win.exe. 
The requested value reflects the current size. For the multithreaded 
version the console that is associated with the
user_inputstream is used.