Yeah, zedit.c
Search for the static function zedit_disp_menu, scroll down to where you see the items displayed, and add your stuff in there.
Then you're going to have to add a new variable, OLC_ZONE(d)->planet_name, in order for the send_to_char to work, which is going to require you to make an addition for the zone_data in db.c struct zone_data, possibly something to the effect of char *planetname; in the struct.
Now, in order for the mud to not hang when you're doing this, you're going to have to add a connectedness state to oasis.h, in the zedit connectedness defined macro list something like
#define ZEDIT_ZONE_PLANETNAME <next number> (dont forget to update the MAX_ZEDIT_ZONE if there is one, i'm doing this from memory so I apologize.
What else... OH yeah, the saving and loading:
in genzon.c in the create_new_zone function, you're going to add a new struct member for planetname so it reserves a spot for the new property.
also in genzon.c in the save_zone function, add some code to make sure the zone gets written to file properly, something like this should do:
/* Print zone header to file. */
fprintf(zfile, "#%d\n"
"%s~\n"
"%s~\n"
++ "%s~\n"
"%hd %hd %d %d %d %d\n",
zone_table[zone_num].number,
(zone_table[zone_num].name && *zone_table[zone_num].name) ? zone_table [zone_num].name : "undefined",
(zone_table[zone_num].builders && *zone_table[zone_num].builders) ? zone_table[zone_num].builders : "None."
++ (zone_table[zone_num].builder && *zone_table[zon_num].planetname) ? zone_table[zone_num].planetname : "None."
genolc_zone_bottom(zone_num),
zone_table[zone_num].top,
zone_table[zone_num].lifespan,
zone_table[zone_num].reset_mode,
zone_table[zone_num].min_level,
zone_table[zone_num].max_level
);
Update the 2nd part of the function as well, the one that checks for types of zone files
to LOAD go to db.c and go to the load_zones function, you will see something like:
line_num += get_line(fl, buf);
if ((ptr = strchr(buf, '~')) != NULL) /* take off the '~' if it's there */
*ptr = '\0';
Z.builders = strdup(buf);
Duplicate this for your planetname info.
To be able to edit this from zedit, you're going to have to add a new part to ZEDIT_MAIN_MENU for the new setting, and a new ZEDIT_ZONE_PLANETNAME case to display your new mini-menu for inputting the name of the zone to zedit_parse function.
Its a relatively complicated task for people not too familiar with modifying OLC. Let me know if you run into trouble
Hope this helps