curs_pad(3X) Library calls curs_pad(3X)

newpad, subpad, prefresh, pnoutrefresh, pechochar, pecho_wchar - create and display curses pads

#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);

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(3X); use prefresh or pnoutrefresh instead.

newpad creates and returns a pointer to a new pad data structure with the given number of lines, nlines, and columns, ncols.

subpad creates and returns a pointer to a subwindow within a pad with the given number of lines, nlines, and columns, ncols. Unlike subwin(3X), 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(3X) or touchline(3X) on parent before calling prefresh.

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

  • 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 is functionally equivalent to calling waddch(3X) 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 is functionally equivalent to calling wadd_wch(3X) 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.

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 specify any error conditions. In this implementation

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.

pechochar may be a macro.

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.

X/Open Curses, 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
  • ensures that dupwin and getwin treat pads versus windows consistently.

curses(3X), curs_addch(3X), curs_refresh(3X), curs_touch(3X)

2024-04-27 ncurses 6.5