The clear and wclear routines are like erase and werase, but they also call clearok, so that the screen is cleared completely on the next call to wrefresh for that window and repainted from scratch.
The clrtobot and wclrtobot routines erase from the cursor to the end of screen. That is, they erase all lines below the cursor in the window. Also, the current line to the right of the cursor, inclusive, is erased.
The clrtoeol and wclrtoeol routines erase the current line to the right of the cursor, inclusive, to the end of the current line.
Blanks created by erasure have the current background rendition (as set by wbkgdset) merged into them.
X/Open defines no error conditions. In this implementation, functions using a window pointer parameter return an error if it is null.
Some historic curses implementations had, as an undocumented feature, the ability to do the equivalent of clearok(..., 1) by saying touchwin(stdscr) or clear(stdscr). This will not work under ncurses.
This implementation, and others such as Solaris, sets the current position to 0,0 after erasing via werase and wclear. That fact is not documented in other implementations, and may not be true of implementations which were not derived from SVr4 source.
Not obvious from the description, most implementations clear the screen after wclear even for a subwindow or derived window. If you do not want to clear the screen during the next wrefresh, use werase instead.