pad(3NCURSES) Library calls pad(3NCURSES)
NAME
newpad, subpad, prefresh, pnoutrefresh, pechochar, pecho_wchar - create
and display curses pads
SYNOPSIS
#include <curses.h>
WINDOW *newpad(int nlines, int ncols);
WINDOW *subpad(WINDOW *parent, int nlines, int ncols,
int begin_y, int begin_x);
int prefresh(WINDOW *pad, int pminrow, int pmincol,
int sminrow, int smincol, int smaxrow, int smaxcol);
int pnoutrefresh(WINDOW *pad, int pminrow, int pmincol,
int sminrow, int smincol, int smaxrow, int smaxcol);
int pechochar(WINDOW *pad, chtype ch);
int pecho_wchar(WINDOW *pad, const cchar_t *wch);
DESCRIPTION
A curses 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 re-
freshed by scrolling or input-echoing operations.
Pads cannot be refreshed with wrefresh(3NCURSES); use prefresh or
pnoutrefresh instead.
newpad
newpad creates and returns a pointer to a new pad data structure with
the given number of lines, nlines, and columns, ncols.
subpad
subpad creates and returns a pointer to a subwindow within a pad with
the given number of lines, nlines, and columns, ncols. Unlike
subwin(3NCURSES), which uses screen coordinates, the new pad is placed
at position (begin_y, begin_x) relative to its parent. Thus, changes
made to one pad can affect both. When operating on a subpad, it is of-
ten necessary to call touchwin(3NCURSES) or touchline(3NCURSES) on par-
ent before calling prefresh.
prefresh, pnoutrefresh
prefresh and pnoutrefresh are analogous to wrefresh(3NCURSES) and
wnoutrefresh(3NCURSES) except that they operate on pads rather than win-
dows. They require additional parameters are needed to indicate what
portions of the pad and screen are involved.
• pminrow and pmincol specify the upper left-hand corner of a rectan-
gular view of the pad.
• sminrow, smincol, smaxrow, and smaxcol specify the vertices of the
rectangle to be displayed on the screen.
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. curses treats negative values of any of these
parameters as zero.
pechochar
pechochar is functionally equivalent to calling waddch(3NCURSES) fol-
lowed by prefresh. It suggests to the curses optimizer that only a sin-
gle character is being output; a considerable performance benefit may be
thus enjoyed. The location of the character ch written to the pad is
used to populate the arguments to prefresh.
pecho_wchar
pecho_wchar is functionally equivalent to calling wadd_wch(3NCURSES)
followed by prefresh. It suggests to the curses optimizer that only a
single wide character is being output; a considerable performance bene-
fit may be thus enjoyed. The location of the character wch written to
the pad is used to populate the arguments to prefresh.
RETURN VALUE
Functions that return an integer return ERR upon failure and OK upon
successful completion.
Functions that return pointers return NULL on error, and set errno to
ENOMEM.
In this implementation
prefresh and pnoutrefresh
return 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.
pechochar
returns ERR if the window is not really a pad, and the associ-
ated call to wechochar returns ERR.
pecho_wchar
returns ERR if the window is not really a pad, and the associ-
ated call to wecho_wchar returns ERR.
NOTES
pechochar may be implemented as a macro.
curses documentation is traditionally averse to motivating the term
“pad”. The Apollo Aegis workstation operating system (circa 1981) sup-
ported a graphical pad feature.
• These graphical pads could be much larger than the computer's dis-
play.
• The read-only output from a command could be scrolled back to in-
spect and select text from the pad.
The two uses may be related.
PORTABILITY
X/Open Curses Issue 4 describes these functions. It specifies no error
conditions for them.
SVr4 describes a successful return value only as “an integer value other
than ERR”.
The behavior of subpad if the parent window is not a pad is undocu-
mented, and is not checked by the vendor Unix implementations.
• SVr4 curses's newpad sets a flag in the WINDOW structure indicating
that the window is a pad.
However, it uses this information only in waddch (to decide if it
should call wrefresh) and wscrl (to avoid scrolling a pad); its
wrefresh does not check it to ensure that a pad is properly updated.
• Solaris xcurses checks whether a window is a pad in its
wnoutrefresh, returning ERR in that case.
However, it sets the flag on subwindows only if the parent window is
a pad. Its newpad does not set this information. Consequently, the
check never fails.
It makes no comparable check in pnoutrefresh — though interestingly
enough, a comment in the source code states that the lack of a check
was an MKS extension.
• NetBSD 7 curses sets a flag in the WINDOW structure for newpad and
subpad, aiding itself to distinguish between wnoutrefresh and
pnoutrefresh.
It does not check for the case where a subwindow is created in a pad
using subwin or derwin.
Its dupwin returns a regular window when duplicating a pad. Like-
wise, its getwin always returns a window, even if the saved data was
from a pad.
ncurses:
• sets a flag in the WINDOW structure for newpad and subpad,
• allows a subwin or derwin call to succeed having a pad parent by
forcing the subwindow to be a pad,
• checks in both wnoutrefresh and pnoutrefresh to ensure that pads and
windows are handled distinctly, and
• ensures that dupwin and getwin treat pads versus windows consis-
tently.
HISTORY
SVr2 (1984) introduced newpad, prefresh, and pnoutrefresh, documenting
them in a single line each.
SVr3 (1987) added subpad and pechochar, and provided more extensive doc-
umentation.
The System V Interface Definition, Version 4 (1995), specified a func-
tion named pechowchar. This was a later addition to SVr4.x, not appear-
ing in the first SVr4 (1989). It differs from X/Open's later
pecho_wchar in that its wstr parameter was a chtype instead of a
wchar_t, and was not const-qualified.
SEE ALSO
ncurses(3NCURSES), addch(3NCURSES), refresh(3NCURSES), touch(3NCURSES)
ncurses 6.5 2025-01-18 pad(3NCURSES)
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