ncurses/man/curs_pad.3x

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.\" $Id: curs_pad.3x,v 1.81 2025/08/23 22:50:00 tom Exp $
.TH curs_pad 3X 2025-08-23 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
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.SH NAME
\fB\%newpad\fP,
\fB\%subpad\fP,
\fB\%prefresh\fP,
\fB\%pnoutrefresh\fP,
\fB\%pechochar\fP,
\fB\%pecho_wchar\fP \-
create and display \fIcurses\fR pads
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBWINDOW *newpad(int \fInlines\fP, int \fIncols\fP);
\fBWINDOW *subpad(WINDOW *\fIparent\fP, int \fInlines\fP, int \fIncols\fP,
      \fBint \fIbegin_y\fB, int \fIbegin_x\fB);\fR
.PP
\fBint prefresh(WINDOW *\fIpad\fB, int \fIpminrow\fB, int \fIpmincol\fB,\fR
      \fBint \fIsminrow\fB, int \fIsmincol\fB, int \fIsmaxrow\fB, int \fIsmaxcol\fB);\fR
\fBint pnoutrefresh(WINDOW *\fIpad\fB, int \fIpminrow\fB, int \fIpmincol\fB,\fR
      \fBint \fIsminrow\fB, int \fIsmincol\fB, int \fIsmaxrow\fB, int \fIsmaxcol\fB);\fR
.PP
\fBint pechochar(WINDOW *\fIpad\fB, chtype \fIch\fB);\fR
\fBint pecho_wchar(WINDOW *\fIpad\fB, const cchar_t *\fIwch\fB);\fR
.fi
.SH DESCRIPTION
A
.I curses
.I pad
is like a window,
except that it is not restricted by the screen size,
and is not necessarily associated with a particular part of the screen.
Pads can be used when a large window is needed,
only part of which is to be visible on the screen.
Pads are not automatically refreshed by scrolling or input-echoing
operations.
.PP
Pads cannot be refreshed with \fB\%wrefresh\fP(3X);
use
.B \%prefresh
or
.B \%pnoutrefresh
instead.
.SS newpad
.B \%newpad
creates and returns a pointer to a new pad data structure
with the given number of lines,
.IR nlines ,
and columns,
.IR ncols .
.SS subpad
.B \%subpad
creates and returns a pointer to a subwindow within a pad
with the given number of lines,
.IR nlines ,
and columns,
.IR ncols .
Unlike \fB\%subwin\fP(3X),
which uses screen coordinates,
the new pad is placed at position
.RI ( begin_y ,
.IR begin_x )
relative to its parent.
Thus,
changes made to one pad can affect both.
When operating on a subpad,
it is often necessary to call \fB\%touchwin\fP(3X) or
\fB\%touchline\fP(3X) on
.I parent
before calling
.BR \%prefresh .
.SS "prefresh, pnoutrefresh"
.B \%prefresh
and
.B \%pnoutrefresh
are analogous to \fB\%wrefresh\fP(3X) and \fB\%wnoutrefresh\fP(3X)
except that they operate on pads rather than windows.
They require additional parameters are needed to indicate what portions
of the pad and screen are involved.
.bP
.I pminrow
and
.I pmincol
specify the upper left-hand corner of a rectangular view of the pad.
.bP
.IR sminrow ,
.IR smincol ,
.IR smaxrow ,
and
.I smaxcol
specify the vertices of the rectangle to be displayed on the screen.
.PP
The lower right-hand corner
of the rectangle to be displayed in the pad
is calculated from the screen coordinates,
since the rectangles must be the same size.
Both rectangles must be entirely contained
within their respective structures.
.I curses
treats
negative values of any of these parameters as zero.
.SS pechochar
.B \%pechochar
is functionally equivalent to calling \fB\%waddch\fP(3X) followed by
.BR \%prefresh .
It suggests to the
.I curses
optimizer that only a single character is being output;
a considerable performance benefit may be thus enjoyed.
The location of the character
.I ch
written to the pad is used to populate the arguments to
.BR \%prefresh .
.SS pecho_wchar
.B \%pecho_wchar
is functionally equivalent to calling \fB\%wadd_wch\fP(3X) followed by
.BR \%prefresh .
It suggests to the
.I curses
optimizer that only a single wide character is being output;
a considerable performance benefit may be thus enjoyed.
The location of the character
.I wch
written to the pad is used to populate the arguments to
.BR \%prefresh .
.SH RETURN VALUE
Functions that return an integer return
.B ERR
upon failure and
.B OK
upon successful completion.
.PP
Functions that return pointers return a null pointer on failure,
and set
.I \%errno
to
.BR \%ENOMEM "."
.PP
In this implementation
.RS 3
.TP 5
.BR prefresh\  and\  pnoutrefresh
return
.B ERR
if the window pointer is null, or
if the window is not really a pad or
if the area to refresh extends off-screen or
if the minimum coordinates are greater than the maximum.
.TP 5
.B pechochar
returns
.B ERR
if the window is not really a pad,
and the associated call to
.B \%wechochar
returns
.BR ERR "."
.TP 5
.B pecho_wchar
returns
.B ERR
if the window is not really a pad,
and the associated call to
.B \%wecho_wchar
returns
.BR ERR "."
.RE
.SH NOTES
.B \%pechochar
may be implemented as a macro.
.PP
.I curses
documentation is traditionally averse to motivating the term
\*(``pad\*(''.
The Apollo Aegis workstation operating system
.RI ( circa
1981)
supported a graphical pad feature.
.bP
These graphical pads could be much larger than the computer's display.
.bP
The read-only output from a command could be scrolled back to inspect
and select text from the pad.
.PP
The two uses may be related.
.SH PORTABILITY
X/Open Curses Issue\ 4 describes these functions.
It specifies no error conditions for them.
.PP
SVr4 describes a successful return value only as
\*(``an integer value other than
.IR ERR \*(''. \" Courier roman in source; SVID 4, vol. 3, p. 524
.PP
The behavior of
.I \%subpad
if the parent window is not a pad is undocumented,
and is not checked by the vendor Unix implementations.
.bP
SVr4
.IR curses 's
.I \%newpad
sets a flag in the
.I \%WINDOW
structure indicating that the window is a pad.
.IP
However,
it uses this information only in
.I \%waddch
(to decide if it should call
.IR \%wrefresh ")"
and
.I \%wscrl
(to avoid scrolling a pad);
its
.I \%wrefresh
does not check it to ensure that a pad is properly updated.
.bP
Solaris
.I \%xcurses
checks whether a window is a pad in its
.IR \%wnoutrefresh ","
returning
.I ERR
in that case.
.IP
However,
it sets the flag on subwindows only if the parent window is a pad.
Its
.I \%newpad
does not set this information.
Consequently,
the check never fails.
.IP
It makes no comparable check in
.I \%pnoutrefresh
\(em though interestingly enough,
a comment in the source code states that the lack of a check
was an MKS extension.
.bP
NetBSD\ 7
.I curses
sets a flag in the
.I \%WINDOW
structure for
.I \%newpad
and
.IR \%subpad ","
aiding itself to distinguish between
.I \%wnoutrefresh
and
.IR \%pnoutrefresh "."
.IP
It does not check for the case where a subwindow is created in
a pad using
.I \%subwin
or
.IR \%derwin "."
.IP
Its
.I \%dupwin
returns a regular window when duplicating a pad.
Likewise,
its
.I \%getwin
always returns a window,
even if the saved data was from a pad.
.PP
.IR \%ncurses ":"
.bP
sets a flag in the
.I \%WINDOW
structure for
.I \%newpad
and
.IR \%subpad ","
.bP
allows a
.I \%subwin
or
.I \%derwin
call to succeed having a pad parent
by forcing the subwindow to be a pad,
.bP
checks in both
.I \%wnoutrefresh
and
.I \%pnoutrefresh
to ensure that pads and windows are handled distinctly,
and
.bP
ensures that
.I \%dupwin
and
.I \%getwin
treat pads versus windows consistently.
.SH HISTORY
SVr2 (1984) introduced
.IR \%newpad ","
.IR \%prefresh ","
and
.IR \%pnoutrefresh ","
documenting them in a single line each.
.PP
SVr3 (1987) added
.I \%subpad
and
.IR \%pechochar ","
and provided more extensive documentation.
.PP
The System\ V Interface Definition,
Version 4 (1995),
specified a function named
.IR \%pechowchar "."
This was a later addition to
.RI SVr4. x ,
not appearing in the first SVr4 (1989).
It differs from X/Open's later
.I \%pecho_wchar
in that its
.I wstr
parameter was a
.I \%chtype
instead of a
.IR \%wchar_t ","
and was not
.IR const "-qualified."
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_addch\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_touch\fP(3X)