Null List

ID:264665
 
Feb 22 2010, 10:27 pm
Code:
world/New()
    if(fexists("Config.sav"))
        var/savefile/S=new("Config.sav")
        S["Ban"]>>Banned    
        
world/Del()
    var/savefile/S=new("Config.sav")
    S["Ban"]<<Banned    

var
    list/Banned=list()
    
mob/verb/Ban(mob/M as mob in world)
    Banned.Add(M)
    
mob/verb/BanList()
    for(var/mob/M in Banned)
        usr<<"[M.key]"


Problem description:
runtime error: Cannot execute null.Add().
proc name: Ban (/mob/verb/Ban)
source file: GM.dm,21
usr: Zorro de las nueve colas (/mob)
src: Zorro de las nueve colas (/mob)
call stack:
Zorro de las nueve colas (/mob): Ban(Zorro de las nueve colas (/mob)), Obv This is a DEMO, not the Real Code.
#1 Feb 22 2010, 10:56 pm
If this isn't the real code then check the real code and look at where banned is defined. If it looks like that does it shouldn't be saying that. If it's just var/list/banned or var/list/banned[] it will cause that.
#2 Feb 22 2010, 11:06 pm
In response to Ulterior Motives (#1)
its var/list/Banned = list()
#3 Feb 22 2010, 11:35 pm
In response to Zorro de las nueve colas (#2)
I've been testing it out and I'm not receiving this runtime error. So, I don't know, it's working perfect for me.
#4 Feb 23 2010, 12:24 am
In response to Ulterior Motives (#3)
I get that runtime everytime i open the BanList
#5 Feb 23 2010, 12:52 am
The savefile contains a null entry for "Ban", which ends up overriding the default of an empty (but non-null) list. You can catch it like so:

S["Ban"]>>Banned
if(!Banned) Banned = list()


Or, if you just delete Config.sav (while the world isn't running) it should fix itself.
#6 Feb 23 2010, 12:59 am
In response to Garthor (#5)
oh Thanks Garthor. and Ulterior.
#7 Feb 23 2010, 10:49 am
In response to Garthor (#5)
Garthor wrote:
The savefile contains a null entry for "Ban", which ends up overriding the default of an empty (but non-null) list. You can catch it like so:

S["Ban"]>>Banned
> if(!Banned) Banned = list()


Or, if you just delete Config.sav (while the world isn't running) it should fix itself.

I'm trying to understand this error. Would this be similar to a dangling pointer?
#8 Feb 23 2010, 12:33 pm
In response to Hulio-G (#7)
Not really, no. It's a null pointer error, which is considerably less severe. A dangling pointer is where you'd have a pointer pointing to a random block of memory. A null pointer is when it's pointing to null, or 0, which is perfectly valid so long as it's recognized as a "do not attempt to dereference this pointer" value.

Again, the issue was simply that the savefile had no entry for the value being read, so it just read out null into the list, overriding it, and then in the future saving the new value of null in the savefile.