# curs_util 3x 2025-08-23 ncurses 6.5 Library calls

    curs_util(3x)                    Library calls                   curs_util(3x)

## NAME

           delay_output,  filter,  flushinp,  getwin, key_name, keyname, nofilter,
           putwin, unctrl, use_env, use_tioctl,  wunctrl  -  miscellaneous  curses
           utility routines

## SYNOPSIS

           #include <curses.h>

           const char * unctrl(chtype ch);
           wchar_t * wunctrl(cchar_t * wch);

           const char * keyname(int c);
           const char * key_name(wchar_t wc);

           void filter(void);
           /* extension */
           void nofilter(void);

           void use_env(bool bf);
           /* extension */
           void use_tioctl(bool bf);

           int putwin(WINDOW * win, FILE * filep);
           WINDOW * getwin(FILE * filep);

           int delay_output(int ms);

           int flushinp(void);

## DESCRIPTION

### unctrl, wunctrl

           unctrl   returns   a   null-terminated   character   string   printably
           representing the curses character ch,  often  one  that  originated  in
           keyboard input; see getch(3x).

           o   Printable   characters  represent  themselves  as  a  one-character
               string.

           o   Control characters are expressed in ^X notation,  where  X  is  the
               printable  symbol  of  the  control  code's  value  plus  32 in the
               ISO 646/"ASCII" character set.

           o   DEL (character code 127) is represented as ^?.

           o   A character code greater than 127 is  represented  in  one  of  two
               ways.

               If  the  screen  has  not  been initialized or is in meta mode (see
               meta(3x)), it  is  expressed  in  M-X  notation,  where  X  is  the
               representation of the code's value minus 128, as described above.

               If the screen is not in meta mode, the character code is assumed to
               represent itself.  It nevertheless may not be  printable;  this  is
               the case for character codes 128-159 in ISO 8859 encodings.

               ncurses's   use_legacy_coding(3x)   function   configures  unctrl's
               handling of these character codes.

           wunctrl  returns  a  null-terminated  wide-character  string  printably
           representing the curses complex character wch.

           Both  functions ignore the attributes and color pair selection of their
           argument.

### keyname, key_name

           The keyname routine returns a character string corresponding to the key
           c.  Key codes are different from character codes.

           o   Key  codes  below  256  are  characters.   They are displayed using
               unctrl.

           o   Values above 256 may be the codes for function keys.  The  function
               key name is displayed.

           o   Otherwise  (if  there is no corresponding name and the key is not a
               character) the function returns null, to denote an  error.   X/Open
               also   lists   an   "UNKNOWN   KEY"   return   value,   which  some
               implementations return rather than null.

           The  corresponding  key_name  returns  a  multibyte  character   string
           corresponding  to  the  wide-character  value  wc.   The  two functions
           (keyname and key_name) do not return the same set of strings:

           o   keyname returns null where key_name would display a meta character.

           o   key_name does not return the name of a function key.

### filter, nofilter

           The filter routine, if used, must be called before initscr  or  newterm
           are called.  Calling filter causes these changes in initialization:

           o   LINES is set to 1;

           o   the  capabilities  clear,  cud1,  cud,  cup,  cuu1,  cuu,  vpa  are
               disabled;

           o   the capability ed is disabled if bce is set;

           o   and the home string is set to the value of cr.

           The nofilter routine cancels the effect of  a  preceding  filter  call.
           That  allows  the  caller to initialize a screen on a different device,
           using a different value of $TERM.  The limitation  arises  because  the
           filter routine modifies the in-memory copy of the terminal information.

### use_env

           The  use_env  routine,  if  used,  should  be  called before initscr or
           newterm are  called  (because  those  compute  the  screen  size).   It
           modifies  the way ncurses treats environment variables when determining
           the screen size.

           o   Normally ncurses looks first  at  the  terminal  database  for  the
               screen size.

               If  use_env  was  called  with  FALSE  for parameter, it stops here
               unless use_tioctl was also called with TRUE for parameter.

           o   Then it asks for the screen size via operating  system  calls.   If
               successful, it overrides the values from the terminal database.

           o   Finally  (unless  use_env was called with FALSE parameter), ncurses
               examines the LINES or COLUMNS environment variables, using a  value
               in  those  to  override  the  results  from the operating system or
               terminal database.

               curses also updates the screen size in response to SIGWINCH, unless
               overridden by the LINES or COLUMNS environment variables,

### use_tioctl

           The  use_tioctl  routine,  if  used, should be called before initscr or
           newterm are called (because those  compute  the  screen  size).   After
           use_tioctl  is  called  with  TRUE as an argument, ncurses modifies the
           last step in its computation of screen size as follows:

           o   checks whether the LINES and COLUMNS environment variables are  set
               to a number greater than zero.

           o   for  each,  ncurses  updates the corresponding environment variable
               with the value that it has obtained via operating  system  call  or
               from the terminal database.

           o   ncurses  re-fetches  the value of the environment variables so that
               it is still the environment variables that set the screen size.

           The use_env and use_tioctl routines combine as follows.

                  use_env   use_tioctl   Summary
                  -----------------------------------------------------------------
                  TRUE      FALSE        ncurses  uses  operating   system   calls
                                         unless  overridden  by  LINES  or COLUMNS
                                         environment variables; default.
                  TRUE      TRUE         ncurses updates LINES and  COLUMNS  based
                                         on operating system calls.
                  FALSE     TRUE         ncurses  ignores LINES and COLUMNS, using
                                         operating system calls to obtain size.

### putwin, getwin

           The putwin routine writes all data associated with window (or pad)  win
           into  the  file  to  which filep points.  This information can be later
           retrieved using the getwin function.

           The getwin routine reads window related data  stored  in  the  file  by
           putwin.   The  routine  then creates and initializes a new window using
           that data.  It returns a pointer to the new window.  There  are  a  few
           caveats:

           o   the  data  written  is  a  copy  of  the  WINDOW structure, and its
               associated character cells.  The format differs between  the  wide-
               character  (ncursesw)  and  non-wide  (ncurses) libraries.  You can
               transfer data between the two, however.

           o   the retrieved window is always created as a  top-level  window  (or
               pad), rather than a subwindow.

           o   the  window's character cells contain the color pair value, but not
               the actual color numbers.  If cells in  the  retrieved  window  use
               color  pairs  that  have  not been created in the application using
               init_pair, they will not be colored when the window is refreshed.

### delay_output

           The delay_output routine inserts an ms  millisecond  pause  in  output.
           Employ  this  function  judiciously  when terminal output uses padding,
           because ncurses  transmits  null  characters  (consuming  CPU  and  I/O
           resources)  instead  of  sleeping  and  requesting  resumption from the
           operating system.  Padding is used unless:

           o   the terminal description has npc (no_pad_char) capability, or

           o   the environment variable NCURSES_NO_PADDING is set.

           If padding is not in use, ncurses uses napms to perform the delay.   If
           the  value  of ms exceeds 30,000 (thirty seconds), it is capped at that
           value.

### flushinp

           The flushinp routine throws away any typeahead that has been  typed  by
           the user and has not yet been read by the program.

## RETURN VALUE

           Except  for  flushinp,  functions  that return integers return ERR upon
           failure and OK upon success.

           Functions that return pointers return a null pointer on failure.

           In ncurses,

           o   flushinp returns ERR if the terminal was not initialized, and

           o   putwin returns ERR if its associated write(2) calls return ERR.

## NOTES

           wunctrl is part of ncurses's wide-character API, and is  not  available
           in its non-wide-character configuration.

## PORTABILITY

           X/Open Curses Issue 4 describes these functions.  It specifies no error
           conditions for them.

           SVr4 describes a successful return value  only  as  "an  integer  value
           other than ERR".

### filter

           The  SVr4  documentation  describes  the  action  of filter only in the
           vaguest terms.  The description here  is  adapted  from  X/Open  Curses
           (which erroneously fails to describe the disabling of cuu).

### delay_output padding

           The  limitation  to  30  seconds and the use of napms differ from other
           implementations.

           o   SVr4 curses does not delay if no padding character is available.

           o   NetBSD curses uses napms when no padding  character  is  available,
               but  does  not  take  timing  into  account  when using the padding
               character.

           Neither limits the delay.

### keyname

           The keyname function  may  return  the  names  of  user-defined  string
           capabilities  that  are defined in the terminfo entry via the -x option
           of tic.  This implementation  automatically  assigns  at  run-time  key
           codes to user-defined strings that begin with "k".  The key codes start
           at KEY_MAX, but are not guaranteed to be the same value  for  different
           runs   because   user-defined   codes  are  merged  from  all  terminal
           descriptions  that  have  been  loaded.    The   use_extended_names(3x)
           function  controls  whether  this  data  is  loaded  when  the terminal
           description is read by the library.

### nofilter, use_tioctl

           The nofilter and use_tioctl routines are  specific  to  ncurses.   They
           were  not  supported on Version 7, BSD or System V implementations.  It
           is recommended  that  any  code  depending  on  ncurses  extensions  be
           conditioned using NCURSES_VERSION.

### putwin/getwin file-format

           The putwin and getwin functions have several issues with portability:

           o   The   files   written   and   read   by   these  functions  use  an
               implementation-specific format.  Although the format is an  obvious
               target for standardization, it has been overlooked.

               Interestingly  enough,  according to the copyright dates in Solaris
               source, the functions (along with scr_init, etc.)  originated  with
               the University of California, Berkeley (in 1982) and were later (in
               1988) incorporated into SVr4.  Oddly, there are no  such  functions
               in the 4.3BSD curses sources.

           o   Most implementations simply dump the binary WINDOW structure to the
               file.  These include SVr4 curses, NetBSD curses, and  PDCurses,  as
               well  as  older  ncurses versions.  This implementation (as well as
               xcurses, the X/Open variant of Solaris  curses,  dated  1995)  uses
               textual dumps.

               The  implementations  that use binary dumps use block I/O (write(2)
               and read(2) functions).  Those that use textual dumps use  buffered
               I/O.  A few applications may happen to write extra data in the file
               using these functions.  Doing that can  run  into  problems  mixing
               block and buffered I/O.  This implementation reduces the problem on
               writes by flushing  the  output.   However,  reading  from  a  file
               written using mixed schemes may not be successful.

### unctrl, wunctrl

           X/Open Curses Issue 4 describes these functions.  It specifies no error
           conditions for them.  It states that unctrl and wunctrl will  return  a
           null  pointer  if  unsuccessful.   This implementation checks for three
           cases:

           o   the parameter is a 7-bit US-ASCII code.   This  is  the  case  that
               X/Open Curses documented.

           o   the parameter is in the range 128-159, i.e., a C1 control code.  If
               use_legacy_coding(3x) has been called with a  2  parameter,  unctrl
               returns  the  parameter,  i.e.,  a  one-character  string  with the
               parameter as the first  character.   Otherwise,  it  returns  "~@",
               "~A", etc., analogous to "^@", "^A", C0 controls.

               X/Open Curses does not document whether unctrl can be called before
               initializing curses.  This implementation permits that, and returns
               the "~@", etc., values in that case.

           o   parameter values outside the 0 to 255 range.  unctrl returns a null
               pointer.

           The strings returned by unctrl in this implementation are determined at
           compile  time,  showing C1 controls from the upper-128 codes with a "~"
           prefix  rather  than  "^".   Other   implementations   have   different
           conventions.    For  example,  they  may  show  both  sets  of  control
           characters with "^", and strip the parameter to 7 bits.   Or  they  may
           ignore  C1  controls and treat all of the upper-128 codes as printable.
           This implementation uses 8 bits but  does  not  modify  the  string  to
           reflect  locale.   The use_legacy_coding(3x) function allows the caller
           to change the output of unctrl.

           Likewise, the meta(3x) function allows the caller to change the  output
           of  keyname,  i.e.,  it  determines  whether to use the "M-" prefix for
           "meta"   keys   (codes   in   the   range   128    to    255).     Both
           use_legacy_coding(3x)   and  meta(3x)  succeed  only  after  curses  is
           initialized.  X/Open Curses does not document the  treatment  of  codes
           128 to 159.  When treating them as "meta" keys (or if keyname is called
           before  initializing  curses),  this  implementation  returns   strings
           "M-^@", "M-^A", etc.

           X/Open Curses documents unctrl as declared in <unctrl.h>, which ncurses
           does.  However, ncurses' <curses.h> includes <unctrl.h>,  matching  the
           behavior of SVr4 curses.  Other implementations may not do that.

### use_env, use_tioctl

           If  ncurses  is  configured  to provide the sp-functions extension, the
           state of use_env and use_tioctl may be  updated  before  creating  each
           screen  rather  than  once  only  (curs_sp_funcs(3x)).  This feature of
           use_env is not provided by other implementations of curses.

## HISTORY

           4BSD (1980) introduced unctrl, defining it as a macro in unctrl.h.

           SVr2 (1984) added delay_output, flushinp, and keyname.

           SVr3 (1987) supplied filter.  Later that year,  SVr3.1  brought  getwin
           and  putwin,  reading  and  writing  window  dumps  with  fread(3)  and
           fwrite(3), respectively.

           SVr4 (1989) furnished use_env.

           X/Open Curses Issue 4 (1995) specified key_name and wunctrl.

           ncurses 5.6 (2006) added nofilter, and 6.0 (2015) use_tioctl.

## SEE ALSO

           curses(3x), curs_initscr(3x), curs_inopts(3x), curs_kernel(3x),
           curs_scr_dump(3x), curs_sp_funcs(3x), curs_variables(3x),
           legacy_coding(3x)

    ncurses 6.5                       2025-08-23                     curs_util(3x)