curs_getstr(3X)

Library calls

curs_getstr(3X)

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(3X), 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 prefixed with “mv” first perform cursor movement and fail if the position (y, x) is outside the window boundaries.

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(3X) 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.

•: Starting in 2021 (ncurses 6.3), getnstr sets raw, rather than noraw and cbreak for better compatibility with SVr4-curses, e.g., allowing one to enter a ^C into the buffer.