plucky (3) delay_output.3ncurses.gz

Provided by: ncurses-doc_6.5+20250216-1_all bug

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(3NCURSES).

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

       •   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.

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

       •   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(3NCURSES)), 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(3NCURSES) 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.

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

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

       •   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:

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

       •   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:

       •   LINES is set to 1;

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

       •   the capability ed is disabled if bce is set;

       •   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.

       •   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.

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

       •   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:

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

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

       •   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:

       •   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.

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

       •   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:

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

       •   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 NULL on error.

       In ncurses,

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

       •   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 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.

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

       •   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(3NCURSES) 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:

       •   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.

       •   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 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:

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

       •   the parameter is in the range 128-159, i.e., a C1 control code.  If  use_legacy_coding(3NCURSES)  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.

       •   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(3NCURSES) function allows the caller to change the output of unctrl.

       Likewise,  the  meta(3NCURSES)  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(3NCURSES)  and  meta(3NCURSES) 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  (sp_funcs(3NCURSES)).   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) supplied 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

       ncurses(3NCURSES), initscr(3NCURSES), inopts(3NCURSES), kernel(3NCURSES), scr_dump(3NCURSES),
       sp_funcs(3NCURSES), curses_variables(3NCURSES), legacy_coding(3NCURSES)