.\" $OpenBSD: curs_clear.3,v 1.8 2023/10/17 09:52:08 nicm Exp $
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.\" $Id: curs_clear.3,v 1.8 2023/10/17 09:52:08 nicm Exp $
.TH curs_clear 3 2023-07-01 "ncurses 6.4" "Library calls"
.na
.hy 0
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fBerase\fP,
\fBwerase\fP,
\fBclear\fP,
\fBwclear\fP,
\fBclrtobot\fP,
\fBwclrtobot\fP,
\fBclrtoeol\fP,
\fBwclrtoeol\fP \- clear all or part of a \fBcurses\fP window
.ad
.hy
.SH SYNOPSIS
\fB#include <curses.h>\fP
.sp
\fBint erase(void);\fP
.br
\fBint werase(WINDOW *\fIwin\fB);\fR
.sp
\fBint clear(void);\fP
.br
\fBint wclear(WINDOW *\fIwin\fB);\fR
.sp
\fBint clrtobot(void);\fP
.br
\fBint wclrtobot(WINDOW *\fIwin\fB);\fR
.sp
\fBint clrtoeol(void);\fP
.br
\fBint wclrtoeol(WINDOW *\fIwin\fB);\fR
.SH DESCRIPTION
.SS erase/werase
The \fBerase\fP and \fBwerase\fP routines copy blanks to every
position in the window, clearing the screen.
.PP
Blanks created by erasure have the current background rendition (as set
by \fBwbkgdset\fP(3)) merged into them.
.SS clear/wclear
The \fBclear\fP and \fBwclear\fP routines are like \fBerase\fP and
\fBwerase\fP, but they also call \fBclearok\fP(3), so that the screen is
cleared completely on the next call to \fBwrefresh\fP for that window
and repainted from scratch.
.SS clrtobot/wclrtobot
The \fBclrtobot\fP and \fBwclrtobot\fP 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.
.SS clrtoeol/wclrtoeol
The \fBclrtoeol\fP and \fBwclrtoeol\fP routines erase the current line
to the right of the cursor, inclusive, to the end of the current line.
.SH RETURN VALUE
All routines return the integer \fBOK\fP on success and \fBERR\fP on failure.
.PP
X/Open defines no error conditions.
In this implementation,
.bP
functions using a window pointer parameter return an error if it is null
.bP
\fBwclrtoeol\fP returns an error
if the cursor position is about to wrap.
.SH NOTES
Note that \fBerase\fP, \fBwerase\fP, \fBclear\fP, \fBwclear\fP,
\fBclrtobot\fP, and \fBclrtoeol\fP may be macros.
.SH PORTABILITY
These functions are described in the XSI Curses standard, Issue 4.
The
standard specifies that they return \fBERR\fP on failure, but specifies no
error conditions.
.PP
The SVr4.0 manual says that these functions could
return "a non-negative integer if \fBimmedok\fP(3) is set",
referring to the return-value of \fBwrefresh\fP.
In that implementation, \fBwrefresh\fP would return a count of
the number of characters written to the terminal.
.PP
Some historic curses implementations had, as an undocumented feature, the
ability to do the equivalent of \fBclearok(..., 1)\fP by saying
\fBtouchwin(stdscr)\fP or \fBclear(stdscr)\fP.
This will not work under
ncurses.
.PP
This implementation, and others such as Solaris,
sets the current position to 0,0 after erasing
via \fBwerase\fP and \fBwclear\fP.
That fact is not documented in other implementations,
and may not be true of implementations
which were not derived from SVr4 source.
.PP
Not obvious from the description,
most implementations clear the screen after \fBwclear\fP
even for a subwindow or derived window.
If you do not want to clear the screen during the next \fBwrefresh\fP,
use \fBwerase\fP instead.
.SH SEE ALSO
\fBcurses\fP(3),
\fBcurs_outopts\fP(3),
\fBcurs_refresh\fP(3),
\fBcurs_variables\fP(3)