ganked & updated from https://gist.github.com/bluetech/6061368

kb.c

/*
 * gcc ./tmp.c -lxcb -lxcb-xkb -lxkbcommon -lxkbcommon-x11 -g -fsanitize=address -fno-omit-frame-pointer 
 */

#include <assert.h>
#include <err.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <xcb/xcb.h>
#include <xcb/xkb.h>

#include <xkbcommon/xkbcommon.h>
#include <xkbcommon/xkbcommon-x11.h>

struct ctx {
    xcb_connection_t *conn;
};

static const char *
get_atom_name(struct ctx *ctx, xcb_atom_t atom) {
    xcb_get_atom_name_reply_t *reply = NULL;
    char *name;
    int length;
    static char buf[16]; /* fixme */

    if (atom == 0)
        return "<empty>";

		xcb_get_atom_name_cookie_t cookie;
		xcb_generic_error_t *error = NULL;

		cookie = xcb_get_atom_name(ctx->conn, atom);

		reply = xcb_get_atom_name_reply(ctx->conn, cookie, &error);
		if (!reply || error)
				return "<invalid>";

    length = xcb_get_atom_name_name_length(reply);
    name = xcb_get_atom_name_name(reply);

    snprintf(buf, sizeof(buf), "%.*s", length, name);
		free(error);
		free(reply);
    return buf;
}

#define all_name_details                                 \
    (XCB_XKB_NAME_DETAIL_KEYCODES |                      \
     XCB_XKB_NAME_DETAIL_GEOMETRY |                      \
     XCB_XKB_NAME_DETAIL_SYMBOLS |                       \
     XCB_XKB_NAME_DETAIL_PHYS_SYMBOLS |                  \
     XCB_XKB_NAME_DETAIL_TYPES |                         \
     XCB_XKB_NAME_DETAIL_COMPAT |                        \
     XCB_XKB_NAME_DETAIL_KEY_TYPE_NAMES |                \
     XCB_XKB_NAME_DETAIL_KT_LEVEL_NAMES |                \
     XCB_XKB_NAME_DETAIL_INDICATOR_NAMES |               \
     XCB_XKB_NAME_DETAIL_KEY_NAMES |                     \
     XCB_XKB_NAME_DETAIL_KEY_ALIASES |                   \
     XCB_XKB_NAME_DETAIL_VIRTUAL_MOD_NAMES |             \
     XCB_XKB_NAME_DETAIL_GROUP_NAMES |                   \
     XCB_XKB_NAME_DETAIL_RG_NAMES)

static void
get_names(struct ctx *ctx) {
		uint8_t xkb_base_event;
		uint8_t xkb_base_error;
		if (xkb_x11_setup_xkb_extension(ctx->conn,
														XKB_X11_MIN_MAJOR_XKB_VERSION,
														XKB_X11_MIN_MINOR_XKB_VERSION,
														0,
														NULL,
														NULL,
														&xkb_base_event,
														&xkb_base_error) != 1)
        errx(EXIT_FAILURE, "Could not setup XKB extension.");


    xcb_xkb_get_names_reply_t *reply = NULL;

    
		xcb_generic_error_t *error = NULL;
		xcb_xkb_get_names_cookie_t cookie;

		cookie = xcb_xkb_get_names(ctx->conn,
															 XCB_XKB_ID_USE_CORE_KBD,
															 all_name_details);

		reply = xcb_xkb_get_names_reply(ctx->conn, cookie, &error);
		if (!reply || error)
				errx(1, "couldn't get reply for get_names");

    xcb_xkb_get_names_value_list_t list;
    
		void *buffer;

		buffer = xcb_xkb_get_names_value_list(reply);
		xcb_xkb_get_names_value_list_unpack(buffer,
																				reply->nTypes,
																				reply->indicators,
																				reply->virtualMods,
																				reply->groupNames,
																				reply->nKeys,
																				reply->nKeyAliases,
																				reply->nRadioGroups,
																				reply->which,
																				&list);
    
    /* dump group names. */
    
		int length;
		xcb_atom_t *iter;

		length = xcb_xkb_get_names_value_list_groups_length(reply, &list);
		iter = xcb_xkb_get_names_value_list_groups(&list);

		for (int i = 0; i < length; i++) {
				xcb_atom_t group_name = *iter;

				printf("group_name %d: %s\n", i, get_atom_name(ctx, group_name));

				iter++;
		}
		free(reply);
		free(error);
}

int main(void) {
    struct ctx ctx;

    ctx.conn = xcb_connect(NULL, NULL);
    if (!ctx.conn)
        errx(1, "couldn't connect to display");

    get_names(&ctx);

    xcb_disconnect(ctx.conn);
    return 0;
}