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.