The overlay and overwrite routines overlay srcwin on top of dstwin. scrwin and dstwin are not required to be the same size; only text where the two windows overlap is copied. The difference is that overlay is non-destructive (blanks are not copied) whereas overwrite is destructive.
The copywin routine provides a finer granularity of control over the overlay and overwrite routines. Like in the prefresh routine, a rectangle is specified in the destination window, (dminrow, dmincol) and (dmaxrow, dmaxcol), and the upper-left-corner coordinates of the source window, (sminrow, smincol). If the argument overlay is true, then copying is non-destructive, as in overlay.
Routines that return an integer return ERR upon failure, and OK (SVr4 only specifies "an integer value other than ERR") upon successful completion.
Note that overlay and overwrite may be macros.
The XSI Curses standard, Issue 4 describes these functions (adding the const qualifiers). It further specifies their behavior in the presence of characters with multibyte renditions (not yet supported in this implementation).
curses(3), curs_pad(3), curs_refresh(3)