Ubuntu Manpage: newpad, subpad, prefresh, pnoutrefresh, pechochar, pecho_wchar

Provided by: ncurses-doc_6.5+20250216-2_all

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 refreshed 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 often necessary to call touchwin(3NCURSES) or touchline(3NCURSES) on parent
before calling prefresh.

prefresh, pnoutrefresh
prefresh and pnoutrefresh are analogous to wrefresh(3NCURSES) and wnoutrefresh(3NCURSES) 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.

• pminrow and pmincol specify the upper left-hand corner of a rectangular 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) followed by prefresh. It suggests to
the curses optimizer that only a single 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
benefit 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 associated call to wechochar returns ERR.

          pecho_wchar
               returns ERR if the window is not really a pad, and the associated  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) supported a graphical pad feature.

       •   These graphical pads could be much larger than the computer's display.

       •   The read-only output from a command could be scrolled back to inspect 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 undocumented, 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. Likewise, 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 consistently.

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 documentation.

       The System V Interface Definition, Version 4 (1995), specified a function named pechowchar.  This  was  a
       later  addition  to  SVr4.x,  not  appearing  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.