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curs_util(3)                    Library calls                   curs_util(3)


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);

       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 ch:

       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 wch.

       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 Curses does not specify 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 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 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
       X/Open Curses, 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 6.5                       2024-04-20                     curs_util(3)

ncurses 6.5 - Generated Wed May 1 18:46:50 CDT 2024
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