set_leds (3) - Linux Manuals
set_leds: Sets the state of the keyboard LED indicators. Allegro game programming library.
Command to display set_leds manual in Linux: $ man 3 set_leds
 
NAME
set_leds - Sets the state of the keyboard LED indicators. Allegro game programming library.
SYNOPSIS
#include <allegro.h>
void set_leds(int leds);
DESCRIPTION
Overrides the state of the keyboard LED indicators. The parameter is a 
bitmask containing any of the values KB_SCROLOCK_FLAG, KB_NUMLOCK_FLAG, 
and KB_CAPSLOCK_FLAG, or -1 to restore the default behavior. Example:
   /* Cycle led indicators. */
   set_leds(KB_SCROLOCK_FLAG);
   rest(1000);
   set_leds(KB_CAPSLOCK_FLAG);
   rest(1000);
   set_leds(KB_NUMLOCK_FLAG);
   rest(1000);
   set_leds(-1);
   
Note that the led behaviour cannot be guaranteed on some platforms, some
leds might not react, or none at all. Therefore you shouldn't rely only on
them to communicate information to the user, just in case it doesn't get
through.