FSX LUA ~=0 versus ==1 - SOLVED

[Robert Benoit]

Solution: http://www.fsdeveloper.com/forum/threads/lua-0-versus-1.438989/#post-760757


Hi,

I used == in a previous LUA and checking bits worked as expected.

  if ipc.readUB(0x9358) ~= nil then
--        No Autoland
    if logic.And(ipc.readUB(0x9358),1) == 1 then
      MipAnnAutoLandLine2 = 2
    end
--        No Land 3
    if logic.And(ipc.readUB(0x9358),2) == 1 then
      MipAnnAutoLandLine2 = 1
    end
--        Land 2
    if logic.And(ipc.readUB(0x9358),4) == 1 then
      MipAnnAutoLandLine1 = 2
    end
--        Land 3
    if logic.And(ipc.readUB(0x9358),8) == 1 then
      MipAnnAutoLandLine1 = 1
    end
  end

I copied that LUA to make a MasterCaution LUA.

  if ipc.readUB(0x92e3) ~= nil then
--        Warning
    if logic.And(ipc.readUB(0x92e3),1) == 1 then
      MipAnnMasterWarning = 1
    end
--        Caution
    if logic.And(ipc.readUB(0x92e3),2) == 1 then
      MipAnnMasterCaution = 1
    end
  end

But == 1 does not work in this new LUA.

(original MasterCaution gauge at far left, making a larger one at right)



I have to use ~= 0 to read the bits.



Any idea what I'm assuming wrong?

Robert

 

[n4gix]

Per the SDK, the only consistently guaranteed valid Boolean value is zero. The non-zero value may be 1 or -1. Therefore to be guaranteed success, always check for a non-zero return.

 

[Robert Benoit]

Thanks.

I searched the SDK Gauge manual and found nothing for LOGIC or BITWISE that mentionned this.

I also looked through the LUA Library Manual (FSUIPC) and saw no reference either.

Robert

 

[n4gix]

Robert, as far as I know that little bit of "received wisdom" isn't actually documented anywhere officially. I learned it directly from Susan Ashlock, who was the last "Chief XML Architect" in the ACES studio when they were closed down.

(A:SomeVariable,bool) ! if{ DoThis if TRUE } els{ DoThat if FALSE }

will always work since it is checking for a non-zero return to become TRUE, and zero return to become FALSE.