[Solved] Same Value Returns Both 0.0 and NULL from Hashtable

[1)ark_NiTe]

The following code returns true for r == 0.0 and r == null. Can anyone tell me why? I would expect that only r==0.0 would return true.

local unit t = GetTriggerUnit()
local real r = 0.0

//Save 0.0 value to hashtable
call SaveRealBJ(0.0, GetHandleIdBJ(t), 1, udg_hashTable)

//Other actions occur

//Load value from hashtable
set r = LoadRealBJ(GetHandleIdBJ(t), 1, udg_hashTable)

//Check value
if r == 0.0 then
    call BJDebugMsg("r = 0.0")
endif

if r == null then
    call BJDebugMsg("r is null")
endif

set t = null

I'm just starting to learn hashtables and I have been away from JASS for the better part of a year now, so I apologize if this is hashtable 101 and I'm just late to the party. Either way, any help would be very much appreciated.

 

[Dr Super Good]

Can anyone tell me why?

I can think of 2 possible reasons.

1. The null value in JASS has an internal value of 0x00000000 and 0.0 represented in a IEEE 32bit float also has a value of 0x00000000.
2. The real equality comparison operator has strange, non-primitive, behaviour. For example it checks if the numbers are approximately equal with a larger machine epsilon than the real type. There exists reals a and b where by a == b and a != b are both true. The null value might be handled by the equality comparison operator as a special case.

 

[Zwiebelchen]

That's why there are natives to check if a hashtable entry exists or not. It gets rid of this problem elegantly.

 

[1)ark_NiTe]

That's why there are natives to check if a hashtable entry exists or not.

Zwie, could you share those natives here so I can confirm they resolve this issue?

 

[TheLordOfChaos201]

there is an easy method to check these values before Booleans.the simplest solution is to convert it into a string and then check the string

if(value=""+null){
Boolean = false;
}

else
{
\\do normal computing
}

 

[Zwiebelchen]

The hashtable natives are: HaveSavedInteger, HaveSavedBoolean, HaveSavedHandle, etc.

If you store a value of "0" to a hashtable slot, HaveSavedInteger will return true.
If you don't store anything or flushed the entry, it will return false.

 

[1)ark_NiTe]

The hashtable natives are: HaveSavedInteger, HaveSavedBoolean, HaveSavedHandle, etc.

That is exactly what I'm looking for. Thanks!