curs_util(3X) Library calls curs_util(3X)

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

#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);

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

  • Printable characters are displayed as themselves, e.g., a one-character string containing the key.
  • Control characters are displayed in the ^X notation.
  • Printing characters are displayed as is.
  • DEL (character 127) is displayed as ^?.
  • 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.

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 w. 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.

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.

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,

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 if 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 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.

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 which have not been created in the application using init_pair, they will not be colored when the window is refreshed.

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.

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

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

returns an error if the terminal was not initialized.
returns an error if the associated fwrite calls return an error.

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).

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.

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.

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.

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 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.

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:

  • 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(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.
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.

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.

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)

2024-04-20 ncurses 6.5