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

Provided by: ncurses-doc_6.4+20240113-1ubuntu2_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 *orig, 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

newpad
newpad creates and returns a pointer to a new pad data structure with the given number of lines, nlines,
and columns, ncols. A 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, and only a part of the window will be on the screen at one time. Automatic refreshes of pads (as
from scrolling or echoing of input) do not occur.

It is not valid to call wrefresh with a pad argument; call prefresh or pnoutrefresh instead. They
require additional parameters to specify the part of the pad to be displayed and the location on the
screen to be used for the display.

subpad
The subpad routine creates and returns a pointer to a subwindow within a pad with the given number of
lines, nlines, and columns, ncols. Unlike subwin, which uses screen coordinates, the window is at
position (begin_x, begin_y) on the pad. The window is made in the middle of the window orig, so that
changes made to one window affect both windows. During the use of this routine, it will often be
necessary to call touchwin or touchline on orig before calling prefresh.

prefresh, pnoutrefresh
The prefresh and pnoutrefresh routines are analogous to wrefresh and wnoutrefresh except that they relate
to pads instead of windows. The additional parameters are needed to indicate what part of the pad and
screen are involved.

• The pminrow and pmincol parameters specify the upper left-hand corner of the rectangle to be
displayed in the pad.

• The sminrow, smincol, smaxrow, and smaxcol parameters specify the edges 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. Negative values of pminrow, pmincol, sminrow, or smincol are treated
as if they were zero.

pechochar
The pechochar routine is functionally equivalent to a call to addch followed by a call to
refresh(3NCURSES), a call to waddch followed by a call to wrefresh, or a call to waddch followed by a
call to prefresh. The knowledge that only a single character is being output is taken into consideration
and, for non-control characters, a considerable performance gain might be seen by using these routines
instead of their equivalents. In the case of pechochar, the last location of the pad on the screen is
reused for the arguments to prefresh.

pecho_wchar
The pecho_wchar function is the analogous wide-character form of pechochar. It outputs one character to
a pad and immediately refreshes the pad. It does this by a call to wadd_wch followed by a call to
prefresh.

RETURN VALUE

       Functions  that  return  an integer return ERR upon failure and OK (SVr4 specifies only “an integer value
       other than ERR”) upon successful completion.

       Functions that return pointers return NULL on error, and set errno to ENOMEM.

       X/Open Curses does not define any error conditions.  In this implementation

          prefresh and pnoutrefresh
               return an error 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  an error if the window is not really a pad, and the associated call to wechochar returns
               an error.

          pecho_wchar
               returns an error if the window is not really a  pad,  and  the  associated  call  to  wecho_wchar
               returns an error.

NOTES

       pechochar may be a macro.

PORTABILITY

BSD curses has no pad feature.

SVr2 curses (1986) provided the newpad and related functions, documenting them in a single line each.
SVr3 (1987) provided more extensive documentation.

The documentation does not explain the term pad. However, the Apollo Aegis workstation operating system
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.

The XSI Curses standard, Issue 4 describes these functions, without significant change from the SVr3
documentation. It describes no error conditions. 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 sets a flag in the WINDOW structure in newpad which tells if 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), and does not check in wrefresh to ensure that the pad is refreshed properly.

• Solaris xcurses checks whether a window is a pad in wnoutrefresh, returning ERR in that case.

However, it only sets the flag for subwindows if the parent window is a pad. Its newpad function
does not set this information. Consequently, the check will never fail.

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, using this to help with
the distinction between wnoutrefresh and pnoutrefresh.

It does not check for the case where a subwindow is created in a pad using subwin or derwin.

The dupwin function returns a regular window when duplicating a pad. Likewise, getwin always returns
a window, even if the saved data was from a pad.

This implementation

• 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