Scroll to navigation



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 - curses soft label routines


#include <curses.h>

int slk_init(int fmt);

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

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);


The slk* functions manipulate the set of soft function-key labels that exist on many terminals. For those terminals that do not have soft labels, curses takes over the bottom line of stdscr, reducing the size of stdscr and the variable LINES. curses standardizes on eight labels of up to eight characters each. In addition to this, the ncurses implementation supports a mode where it simulates 12 labels of up to five characters each. This is useful for PC-like enduser devices. 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.


The slk_init routine must be called before initscr or newterm is called. If initscr eventually uses a line from stdscr to emulate the soft labels, then fmt determines how the labels are arranged on the screen:

indicates a 3-2-3 arrangement of the labels.
indicates a 4-4 arrangement
indicates the PC-like 4-4-4 mode.
is again the PC-like 4-4-4 mode, but in addition an index line is generated, helping the user to identify the key numbers easily.


The slk_set routine (and the slk_wset routine for the wide-character library) has three parameters:

is the label number, from 1 to 8 (12 if fmt in slk_init is 2 or 3);
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. A null string or a null pointer sets up a blank label.
is either 0, 1, or 2, indicating whether the label is to be left-justified, centered, or right-justified, respectively, within the label.

The slk_label routine returns the current label for label number labnum, with leading and trailing blanks stripped.

Screen updates

The slk_refresh and slk_noutrefresh routines correspond to the wrefresh and wnoutrefresh routines.

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.

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 keys is A_STANDOUT (as in System V curses, which does not document this fact).


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 integer value, e.g., 32-bits.


These routines return ERR upon failure and OK (SVr4 specifies only "an integer value other than ERR") upon successful completion.

X/Open defines no error conditions. In this implementation

returns the attribute used for the soft keys.
return an error if the terminal or the softkeys were not initialized.
returns an error if the terminal or the softkeys were not initialized.
returns an error if the terminal or the softkeys were not initialized, or the color pair is outside the range 0..COLOR_PAIRS-1.
returns an error if the terminal or the softkeys were not initialized, or the color pair is outside the range 0..COLOR_PAIRS-1.
returns an error if the format parameter is outside the range 0..3.
returns NULL on error.
returns an error 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.


SVr3 introduced these functions:

SVr4 added these functions:

X/Open Curses added these:


X/Open Curses documents the opts argument as reserved for future use, saying that it must be null. This implementation uses that parameter in ABI 6 for the functions which have 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.


Most applications would use slk_noutrefresh because a wrefresh is likely to follow soon.


The XSI Curses standard, Issue 4, described the soft-key functions, with some differences from SVr4 curses:

It added functions like the SVr4 attribute-manipulation functions slk_attron, slk_attroff, 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 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 an error.
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.


ncurses(3NCURSES), attr(3NCURSES), initscr(3NCURSES), refresh(3NCURSES), curses_variables(3NCURSES).