derwin — relative window creation function
WINDOW *derwin(WINDOW *orig, int nlines, int ncols, int begin_y,
function creates a new window with nlines lines and ncols columns,
positioned so that the origin is at (begin_y, begin_x)
relative to the origin of the window orig.
If any part of the new window is outside orig,
the function fails and the window is not created.
Upon successful completion, these functions
return a pointer to the new window. Otherwise, they return a null pointer.
No errors are defined.
Before performing the first refresh of a subwindow, portable applications
on the parent window.
Each window maintains internal descriptions of the screen image and status.
The screen image is shared among all windows in the window hierarchy. Refresh
operations rely on information on what has changed within a window, which is
private to each window. Refreshing a window, when updates were made to a
different window, may fail to perform needed updates because the windows do
not share this information.
First released in X/Open Curses, Issue 4.