Ubuntu Manpage: getstr, getnstr, wgetstr, wgetnstr, mvgetstr, mvgetnstr, mvwgetstr, mvwgetnstr

Provided by: ncurses-doc_6.4+20240113-1ubuntu2_all

NAME

       getstr,  getnstr,  wgetstr,  wgetnstr, mvgetstr, mvgetnstr, mvwgetstr, mvwgetnstr - accept
       character strings from curses terminal keyboard

SYNOPSIS

       #include <curses.h>

       int getstr(char *str);
       int getnstr(char *str, int n);
       int wgetstr(WINDOW *win, char *str);
       int wgetnstr(WINDOW *win, char *str, int n);

       int mvgetstr(int y, int x, char *str);
       int mvwgetstr(WINDOW *win, int y, int x, char *str);
       int mvgetnstr(int y, int x, char *str, int n);
       int mvwgetnstr(WINDOW *win, int y, int x, char *str, int n);

DESCRIPTION

       The function wgetnstr is equivalent to a series of  calls  to  wgetch(3NCURSES),  until  a
       newline or carriage return terminates the series:

       •   The terminating character is not included in the returned string.

       •   In all instances, the end of the string is terminated by a NUL.

       •   The function stores the result in the area pointed to by the str parameter.

       •   The  function  reads  at most n characters, thus preventing a possible overflow of the
           input buffer.

           Any attempt to enter more characters (other than the terminating newline  or  carriage
           return) causes a beep.

           Function keys also cause a beep and are ignored.

       The user's erase and kill characters are interpreted:

       •   The  erase  character (e.g., ^H) erases the character at the end of the buffer, moving
           the cursor to the left.

           If keypad mode is on for the window, KEY_LEFT and KEY_BACKSPACE  are  both  considered
           equivalent to the user's erase character.

       •   The  kill  character  (e.g.,  ^U)  erases the entire buffer, leaving the cursor at the
           beginning of the buffer.

       Characters input are echoed only if echo is currently on.   In  that  case,  backspace  is
       echoed as deletion of the previous character (typically a left motion).

       The  getnstr,  mvgetnstr,  mvwgetnstr, and wgetnstr functions are identical to the getstr,
       mvgetstr, mvwgetstr, and wgetstr functions, respectively, except  that  the  *n*  versions
       read at most n characters, letting the application prevent overflow of the input buffer.

RETURN VALUE

       All  of these functions return the integer OK upon successful completion.  (SVr4 specifies
       only “an integer value other than ERR”) If unsuccessful, they return ERR.

       X/Open defines no error conditions.

       In this implementation, these functions return an error

       •   if the window pointer is null,

       •   if its timeout expires without having any data, or

       •   if the associated call to wgetch failed.

       This implementation provides an extension as well.  If a SIGWINCH interrupts the function,
       it will return KEY_RESIZE rather than OK or ERR.

       Functions  with  a  “mv” prefix first perform a cursor movement using wmove, and return an
       error if the position is outside the window, or if the window pointer is null.

NOTES

       Any of these functions other than wgetnstr may be macros.

       Using getstr, mvgetstr, mvwgetstr, or wgetstr to read a  line  that  overflows  the  array
       pointed to by str causes undefined results.  The use of getnstr, mvgetnstr, mvwgetnstr, or
       wgetnstr, respectively, is recommended.

PORTABILITY

These functions are described in The Single Unix Specification, Version 2. No error
conditions are defined.

This implementation returns ERR if the window pointer is null, or if the lower-level
wgetch(3NCURSES) call returns an ERR.

SVr3 and early SVr4 curses implementations did not reject function keys; the SVr4.0
documentation claimed that “special keys” (such as function keys, “home” key, “clear” key,
etc.) are “interpreted”, without giving details. It lied. In fact, the “character” value
appended to the string by those implementations was predictable but not useful (being, in
fact, the low-order eight bits of the key's KEY_ value).

The functions getnstr, mvgetnstr, and mvwgetnstr were present but not documented in SVr4.

X/Open Curses, Issue 5 (2007) stated that these functions “read at most n bytes” but did
not state whether the terminating NUL is counted in that limit. X/Open Curses, Issue 7
(2009) changed that to say they “read at most n-1 bytes” to allow for the terminating NUL.
As of 2018, some implementations count it, some do not:

• ncurses 6.1 and PDCurses do not count the NUL in the given limit, while

• Solaris SVr4 and NetBSD curses count the NUL as part of the limit.

• Solaris xcurses provides both: its wide-character wget_nstr reserves a NUL, but its
wgetnstr does not count the NUL consistently.

In SVr4 curses, a negative value of n tells wgetnstr to assume that the caller's buffer is
large enough to hold the result, i.e., to act like wgetstr. X/Open Curses does not
mention this (or anything related to negative or zero values of n), however most
implementations use the feature, with different limits:

• Solaris SVr4 curses and PDCurses limit the result to 255 bytes. Other Unix systems
than Solaris are likely to use the same limit.

• Solaris xcurses limits the result to LINE_MAX bytes.

• NetBSD 7 assumes no particular limit for the result from wgetstr. However, it limits
the wgetnstr parameter n to ensure that it is greater than zero.

A comment in NetBSD's source code states that this is specified in SUSv2.

• ncurses (before 6.2) assumes no particular limit for the result from wgetstr, and
treats the n parameter of wgetnstr like SVr4 curses.

• ncurses 6.2 uses LINE_MAX, or a larger (system-dependent) value which the sysconf
function may provide. If neither LINE_MAX or sysconf is available, ncurses uses the
POSIX value for LINE_MAX (a 2048 byte limit). In either case, it reserves a byte for
the terminating NUL.

Although getnstr is equivalent to a series of calls to getch, it also makes changes to the
curses modes to allow simple editing of the input buffer:

• getnstr saves the current value of the nl, echo, raw and cbreak modes, and sets nl,
noecho, noraw, and cbreak.

getnstr handles the echoing of characters, rather than relying on the caller to set an
appropriate mode.

• It also obtains the erase and kill characters from erasechar and killchar,
respectively.

• On return, getnstr restores the modes to their previous values.

Other implementations differ in their treatment of special characters:

• While they may set the echo mode, other implementations do not modify the raw mode,
They may take the cbreak mode set by the caller into account when deciding whether to
handle echoing within getnstr or as a side-effect of the getch calls.

• The original ncurses (as pcurses in 1986) set noraw and cbreak when accepting input
for getnstr. That may have been done to make function- and cursor-keys work; it is
not necessary with ncurses.

Since 1995, ncurses has provided signal handlers for INTR and QUIT (e.g., ^C or ^\).
With the noraw and cbreak settings, those may catch a signal and stop the program,
where other implementations allow one to enter those characters in the buffer.