curs_slk(3X)

🎀 curs_slk — library calls 🎀

hiii bestie 💖 so this page is curs_slk(3X) from the library calls chapter of the ncurses manual, and it's literally all about the soft label keys — the little function-key labels chillin' at the bottom of your screen. it's giving group chat energy but for terminal labels. let's go ✨

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✨ NAME ✨

slk_init, slk_set, slk_wset, slk_refresh, slk_noutrefresh, slk_label, slk_clear, slk_restore, slk_touch, slk_attron, slk_attrset, slk_attroff, slk_attr_on, slk_attr_set, slk_attr_off, slk_attr, slk_color, extended_slk_color — the curses soft label key routines 🏷️

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🦋 SYNOPSIS 🦋

#include <curses.h>

int slk_init(int fmt);

int slk_set(int labnum, const char *label, int align);
int slk_wset(int labnum, const wchar_t *label, int align);

char *slk_label(int labnum);

int slk_refresh(void);
int slk_noutrefresh(void);
int slk_clear(void);
int slk_restore(void);
int slk_touch(void);

int slk_attron(const chtype attrs);
int slk_attroff(const chtype attrs);
int slk_attrset(const chtype attrs);
int slk_attr_on(attr_t attrs, void *opts);
int slk_attr_off(const attr_t attrs, void *opts);
int slk_attr_set(const attr_t attrs, short pair, void*opts);
/* extension */
attr_t slk_attr(void);

int slk_color(short pair);
/* extension */
int extended_slk_color(int pair);

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🌸 DESCRIPTION 🌸

okay so these functions are the whole girlboss squad that manipulates the soft function key labels that some hardware terminals support. not every terminal has them tho — and for the ones that don't, curses just takes over the bottom line of stdscr for itself, reducing its vertical size and the value of LINES by one. rude but necessary 💅

by default, curses uses eight labels of up to eight characters each.

ncurses also supports a whole other mode — twelve labels of up to five characters each — following a convention associated with the IBM PC/AT keyboard. ncurses simulates this mode by taking over up to two lines at the bottom of the screen; it does not try to use any hardware support for this mode. no cap.

🔧 Initialization

slk_init must be called before initscr or newterm — like, non-negotiable, bestie. if initscr eventually uses a line from stdscr to emulate the soft labels, then fmt decides how the labels are arranged on the screen:

• 0 — indicates a 3-2-3 arrangement of the labels.
• 1 — indicates a 4-4 arrangement.
• 2 — indicates the PC-like 4-4-4 mode.
• 3 — is again the PC-like 4-4-4 mode, but in addition an index line is generated, helping the user to associate each label with its numbered function key. LINES and the vertical size of stdscr are further reduced.

🏷️ Labels

you populate the labels with normal strings (slk_set) or wide-character strings (slk_wset). each function takes three parameters:

• labnum — is the label number, from 1 to 8 (12 if fmt in slk_init is 2 or 3);
• label — is be the string to put on the label, up to eight (five if fmt in slk_init is 2 or 3) characters in length. an empty string or a null pointer sets up a blank label.
• align — is 0, 1, or 2, aligning label to the left, center, or right, respectively, within the 8 (5) character cells housing it.

slk_label obtains the string assigned to label number labnum, with any leading and trailing blanks stripped. so fresh ✨

🖥️ Screen Updates

slk_refresh and slk_noutrefresh affect the soft key label lines the same way wrefresh and wnoutrefresh do the curses window.

the slk_clear routine clears the soft labels from the screen.

the slk_restore routine restores the soft labels to the screen after a slk_clear has been performed. it's giving comeback era 🫶

the slk_touch routine forces all the soft labels to be output the next time a slk_noutrefresh is performed.

🎨 Video Attributes

the slk_attron, slk_attrset, slk_attroff, and slk_attr routines correspond to attron, attrset, attroff, and attr_get, respectively. they have an effect only if soft labels are simulated on the bottom line of the screen. the default highlight for soft key labels is A_STANDOUT (as in System V curses, which does not document this fact). iykyk 😌

🌈 Colors

the slk_color routine corresponds to color_set. it has an effect only if soft labels are simulated on the bottom line of the screen.

because slk_color accepts only short (signed 16-bit integer) values, this implementation provides extended_slk_color, which accepts an int value of at least 32 bits. glow-up behavior fr fr 💅

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💀 RETURN VALUE 💀

functions that return integers return ERR upon failure and OK upon success.

in ncurses:

• slk_attr — returns the attribute used for the soft keys.
• slk_attroff, slk_attron, slk_clear, slk_noutrefresh, slk_refresh, slk_touch — return ERR if the terminal or the softkeys were not initialized.
• slk_attrset — returns ERR if the terminal or the softkeys were not initialized.
• slk_attr_set — returns ERR if the terminal or the softkeys were not initialized, or the color pair is outside the range 0..COLOR_PAIRS-1.
• slk_color — returns ERR if the terminal or the softkeys were not initialized, or the color pair is outside the range 0..COLOR_PAIRS-1.
• slk_init — returns ERR if the format parameter is outside the range 0..3.
• slk_label — returns NULL on error.
• slk_set — returns ERR if the terminal or the softkeys were not initialized, or the labnum parameter is outside the range of label counts, or if the format parameter is outside the range 0..2, or if memory for the labels cannot be allocated.

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📝 NOTES 📝

most applications would use slk_noutrefresh because a wrefresh is likely to follow soon. efficient queen behavior 👑

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🌟 EXTENSIONS 🌟

X/Open Curses documents the opts argument as reserved for future use, saying that it must be a null pointer. the ncurses 6 ABI uses it for the functions that accept a color pair parameter to support extended color pairs.

for functions which modify the color, e.g., slk_attr_set, if opts is set it is treated as a pointer to int, and used to set the color pair instead of the short pair parameter. sneaky but iconic 💜

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🌍 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”.

• X/Open added functions like the SVr4 attribute-manipulation functions slk_attron, slk_attroff, and slk_attrset, but which use attr_t parameters (rather than chtype), along with a reserved opts parameter.
  • two of these new functions (unlike the SVr4 functions) have no provision for color: slk_attr_on and slk_attr_off.
  • the third function (slk_attr_set) has a color pair parameter.
• it added const qualifiers to parameters (unnecessarily), and
• it added slk_color.

although slk_start is declared in the curses header file, it was not documented by SVr4 other than its presence in a list of libtermlib.so.1 symbols. reading the source code (i.e., Illumos):

• slk_start has two parameters:
  • ng (number of groups) and
  • gp (group pointer).
• soft-key groups are an array of ng integers.
• in SVr4, slk_init calls slk_start passing a null for gp. for this case, slk_start uses the number of groups ng (3 for the 3-2-3 layout, 2 for the 4-4 layout) which slk_init provided. if ng is neither 2 or 3, slk_start checks the terminfo fln (label_format) capability, interpreting that as a comma-separated list of numbers, e.g., “3,2,3” for the 3-2-3 layout. finally, if there is no fln capability, slk_start returns ERR.
• if slk_start is given a non-null gp, it copies the ng elements of the group of soft-keys, up to 16. if there are more than 16 elements, slk_start returns ERR.
• the format codes 2 and 3 for slk_init were added by ncurses in 1996. PDCurses 2.4 added this feature in 2001.

the function slk_attr was added by ncurses in 1996.

X/Open Curses does not specify a limit for the number of colors and color pairs which a terminal can support. however, in its use of short for the parameters, it carries over SVr4's implementation detail for the compiled terminfo database, which uses signed 16-bit numbers. this implementation provides extended versions of those functions which use int parameters, allowing applications to use larger color- and pair-numbers. growth mindset ✨

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📜 HISTORY 📜

SVr3 introduced these functions:

• slk_clear
• slk_init
• slk_label
• slk_noutrefresh
• slk_refresh
• slk_restore
• slk_set
• slk_touch

SVr4 added these functions:

• slk_attroff
• slk_attron
• slk_attrset
• slk_start

X/Open Curses added these:

• slk_attr_off
• slk_attr_on
• slk_attr_set
• slk_color
• slk_wset

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👀 SEE ALSO 👀

curses(3X), curs_attr(3X), curs_initscr(3X), curs_refresh(3X), curs_variables(3X)

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and that's the whole page bestie, no notes, we ate 🍓 this was written against ncurses 6.6 and dated 2025-01-18 — go forth and label those soft keys, mwah 💖🎀🦋