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getstr(3NCURSES) getstr(3NCURSES)

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 *, int y, int x, char *str, int n);

DESCRIPTION

The function getstr is equivalent to a series of calls to getch, until a newline or carriage return is received (the terminating character is not included in the returned string). The resulting value is placed in the area pointed to by the character pointer str, followed by a NUL.

wgetnstr 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 getnstr function reads from the stdscr default window.

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

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).

RETURN VALUE

All routines return the integer ERR upon failure and an OK (SVr4 specifies only “an integer value other than ERR”) upon successful completion.

X/Open defines no error conditions.

In this implementation, these functions return an error if the window pointer is null, or if its timeout expires without having any data.

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

Note that getstr, mvgetstr, and mvwgetstr may be macros.

PORTABILITY

These functions are described in the XSI Curses standard, Issue 4. They read single-byte characters only. The standard does not define any error conditions. 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 do, some do not count it:

  • 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.

SEE ALSO

ncurses(3NCURSES), getch(3NCURSES), curses_variables(3NCURSES).