- 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.
+ The function wgetnstr is equivalent to a series of calls to wgetch(3x),
+ until a newline or carriage return terminates the series:
+
+ o The terminating character is not included in the returned string.
+
+ o In all instances, the end of the string is terminated by a NUL.
+
+ o The function stores the result in the area pointed to by the str
+ parameter.
+
+ o The function reads at most n characters, thus preventing a possible
+ overflow of the input buffer.
- The getnstr function reads from the stdscr default window. The other
- functions, such as wgetnstr, read from the window given as a parameter.
+ Any attempt to enter more characters (other than the terminating
+ newline or carriage return) causes a beep.
- getnstr 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.
+ Function keys also cause a beep and are ignored.
The user's erase and kill characters are interpreted:
- o The erase character (e.g., ^H) erases the character at the end of
+ o 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.
+ both considered equivalent to the user's erase character.
o 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 (typi-
- cally a left motion).
+ 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.
- All routines return the integer ERR upon failure and an OK (SVr4 speci-
- fies only "an integer value other than ERR") upon successful comple-
- tion.
+ 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, or if its timeout expires without having any data.
+ In this implementation, these functions return an error
+
+ o if the window pointer is null,
+
+ o if its timeout expires without having any data, or
+
+ o if the associated call to wgetch failed.
- This implementation provides an extension as well. If a SIGWINCH in-
- terrupts the function, it will return KEY_RESIZE rather than OK or ERR.
+ 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.
+ Functions prefixed with "mv" first perform cursor movement and fail if
+ the position (y, x) is outside the window boundaries.
- Note that getstr, mvgetstr, and mvwgetstr may be macros.
+ 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.
- 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", with-
- out 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).
+ 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.
@@ -140,74 +159,90 @@
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:
+ some implementations count it, some do not:
- o ncurses 6.1 and PDCurses do not count the NUL in the given limit,
+ oncurses 6.1 and PDCurses do not count the NUL in the given limit,
while
o Solaris SVr4 and NetBSD curses count the NUL as part of the limit.
- o Solaris xcurses provides both: its wide-character wget_nstr re-
- serves a NUL, but its wgetnstr does not count the NUL consistently.
+ o 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
+ 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:
- o Solaris SVr4 curses and PDCurses limit the result to 255 bytes.
+ o Solaris SVr4 curses and PDCurses limit the result to 255 bytes.
Other Unix systems than Solaris are likely to use the same limit.
o Solaris xcurses limits the result to LINE_MAX bytes.
- o NetBSD 7 assumes no particular limit for the result from wgetstr.
- However, it limits the wgetnstr parameter n to ensure that it is
+ o 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
+ A comment in NetBSD's source code states that this is specified in
SUSv2.
- o ncurses (before 6.2) assumes no particular limit for the result
- from wgetstr, and treats the n parameter of wgetnstr like SVr4
+ oncurses (before 6.2) assumes no particular limit for the result
+ from wgetstr, and treats the n parameter of wgetnstr like SVr4
curses.
- o 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 ter-
- minating NUL.
+ oncurses 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
+ 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:
- ogetnstr saves the current value of the nl, echo, raw and cbreak
+ ogetnstr 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
+ getnstr handles the echoing of characters, rather than relying on
the caller to set an appropriate mode.
- o It also obtains the erase and kill characters from erasechar and
+ o It also obtains the erase and kill characters from erasechar and
killchar, respectively.
o On return, getnstr restores the modes to their previous values.
- Other implementations differ. While they may set the echo mode, they
- do not modify the raw mode, and 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. Because ncurses sets
- these modes, its signal handlers for INTR and QUIT (e.g., ^C or ^\) may
- catch a signal and stop the program, where other implementations allow
- one to enter those characters in the buffer.
+ Other implementations differ in their treatment of special characters:
+
+ o 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.
+
+ o 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.
+
+ o 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.