curs_pad

Section: Miscellaneous Library Functions (3X)
Updated:
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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

The newpad routine 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 (e.g., from scrolling or echoing of input) do not occur.

It is not legal to call wrefresh with a pad as an argument; the routines prefresh or pnoutrefresh should be called instead. Note that these routines 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.
.IP • 4 The pminrow and pmincol parameters specify the upper left-hand corner of the rectangle to be displayed in the pad.
.IP • 4 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(3X), 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

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

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

X/Open 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

Note that 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:
.IP • 4 These graphical pads could be much larger than the computer's display.
.IP • 4 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:
.IP • 4 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.
.IP • 4 Solaris X/Open Curses checks if 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.
.IP • 4 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
.IP • 4 sets a flag in the WINDOW structure for newpad and subpad,
.IP • 4 allows a subwin or derwin call to succeed having a pad parent by forcing the subwindow to be a pad,
.IP • 4 checks in both wnoutrefresh and pnoutrefresh to ensure that pads and windows are handled distinctly, and
.IP • 4 ensures that dupwin and getwin treat pads versus windows consistently.