# curs_util 3x 2024-01-05 ncurses 6.4 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 c);
           wchar_t *wunctrl(cchar_t *c);

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

           void filter(void);

           void use_env(bool f);

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

           int delay_output(int ms);
           int flushinp(void);

           /* extensions */
           void nofilter(void);
           void use_tioctl(bool f);

## DESCRIPTION

### unctrl

           The  unctrl  routine  returns  a  character string which is a printable
           representation of the character c:

           o   Printable characters are displayed  as  themselves,  e.g.,  a  one-
               character string containing the key.

           o   Control characters are displayed in the ^X notation.

           o   Printing characters are displayed as is.

           o   DEL (character 127) is displayed as ^?.

           o   Values  above 128 are either meta characters (if the screen has not
               been initialized, or if  meta(3x)  has  been  called  with  a  TRUE
               parameter),  shown  in  the  M-X  notation,  or  are  displayed  as
               themselves.  In the latter case, the values may not  be  printable;
               this follows the X/Open specification.

           The  corresponding  wunctrl  returns  a  printable  representation of a
           complex character c.

           In both unctrl and wunctrl the attributes and color associated with the
           character parameter are ignored.

### 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  w.   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  if 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 which set the screen size.

           The use_env and use_tioctl routines combine as follows.

                  use_env   use_tioctl   Summary
                  -----------------------------------------------------------------
                  TRUE      FALSE        This  is  the  default behavior.  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  which  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,  routines that return an integer return ERR upon
           failure and OK (SVr4 specifies only "an integer value other than  ERR")
           upon successful completion.

           Routines that return pointers return NULL on error.

           X/Open does not define any error conditions.  In this implementation

              flushinp
                   returns an error if the terminal was not initialized.

              putwin
                   returns  an  error  if  the  associated  fwrite calls return an
                   error.

## PORTABILITY

### filter

           The SVr4 documentation describes the  action  of  filter  only  in  the
           vaguest  terms.   The  description  here is adapted from the XSI Curses
           standard (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 which are defined in the terminfo entry via the -x  option
           of tic.  This implementation automatically assigns at run-time keycodes
           to user-defined strings which begin with "k".  The  keycodes  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
           which  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 and PDCurses, as well as
               older ncurses versions.  This implementation (as well as the X/Open
               variant of Solaris curses, dated 1995) uses textual dumps.

               The  implementations  which  use  binary  dumps  use block-I/O (the
               fwrite and fread 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

           The  XSI Curses standard, Issue 4 describes these functions.  It states
           that unctrl and wunctrl will return a null pointer if unsuccessful, but
           does  not  define any error conditions.  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.

## 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 6.4                       2024-01-05                     curs_util(3x)