"Stealing" Local Variables from other functions

[Amineri]

As was accidentally discovered by johnnylump recently, it is possible to use a local variable reference in a function that it was not originally defined in.

 

I've played around with this a bit more, and it works generally, not just with local variables that are the same name.

 

That is :: A local variable reference defined / used in one function can be used in another function

 

So far I've only used this for local variables that are defined in a different function but within the same class. Even with that limitation, this will be very useful.

 

Here is the function (new version) decompiled.

 

function InitAlienLoadoutInfos()
{
local int PlayerIndex, iAlienPods;

PlayerIndex = 0;
J0x0B:
// End:0x42E [Loop If]
if(PlayerIndex < 4)
{
// End:0x51
if(m_arrTeamLoadoutInfos[PlayerIndex].m_eTeam == 16)
{
return;
}
// End:0x420
else
{
// End:0x420
if(m_arrTeamLoadoutInfos[PlayerIndex].m_eTeam == 0)
{
m_arrTeamLoadoutInfos[PlayerIndex].m_eTeam = 16;
// End:0x324
if(!m_bUseAlienInfo)
{
iAlienPods = 0;
J0xC5:
// End:0x321 [Loop If]
if(iAlienPods < m_kAlienSquad.arrPods.Length)
{
Index = 0;
J0xFB:
// End:0x313 [Loop If]
if(Index < 5)
{
// End:0x160
if(Index == 0)
{
m_iLowestDifficulty = m_kAlienSquad.arrPods[iAlienPods].eMain;
}
// End:0x1B5
if(Index == 1)
{
m_iLowestDifficulty = m_kAlienSquad.arrPods[iAlienPods].eSupport1;
}
// End:0x20A
if(Index == 2)
{
m_iLowestDifficulty = m_kAlienSquad.arrPods[iAlienPods].eSupport2;
}
// End:0x25F
if(Index == 3)
{
m_iLowestDifficulty = m_kAlienSquad.arrPods[iAlienPods].eMainAltWeapon;
}
// End:0x2B4
if(Index == 4)
{
m_iLowestDifficulty = m_kAlienSquad.arrPods[iAlienPods].eSupport1AltWeapon;
}
// End:0x305
if(m_iLowestDifficulty != 0)
{
m_arrTeamLoadoutInfos[PlayerIndex].m_arrUnits.AddItem(BuildAlienContent(byte(m_iLowestDifficulty), 0));
}
++ Index;
// [Loop Continue]
goto J0xFB;
}
++ iAlienPods;
// [Loop Continue]
goto J0xC5;
}
}
// End:0x41D
else
{
m_arrTeamLoadoutInfos[PlayerIndex].m_arrUnits.AddItem(BuildAlienContent(byte(m_kAlienInfo.iPodLeaderType)));
m_arrTeamLoadoutInfos[PlayerIndex].m_arrUnits.AddItem(BuildAlienContent(byte(m_kAlienInfo.iPodSupporterType)));
m_arrTeamLoadoutInfos[PlayerIndex].m_arrUnits.AddItem(BuildAlienContent(byte(m_kAlienInfo.iRoamingType)));
}
// [Explicit Break]
goto J0x42E;
}
}
++ PlayerIndex;
J0x42E:
// [Loop Continue]
goto J0x0B;
}
return;
}

 

The Index variable is a local variable that was defined in another function (in the same class as this, XGMissionDesc).

 

I suspect that this could get a person into trouble if the local variable used was from a function in the call sequence to the current one.

 

That is, if LocalVar is defined in FunctionA, and FunctionA calls FunctionB, and FunctionB calls FunctionC, and I re-use LocalVar in FunctionC, I suspect it might result in some aberrant behavior when the code returns back to FunctionA.

 

Still, this may be pretty useful to people.

[anUser]

so you just call it using the same hex code it had in it's function? Anyway it's indeed a great finding, I remember discarding a project because I didn't have a counter variable to iterate an array

[johnnylump]

johnnylump, idiot savant of x-com modding :)

[Amineri]

so you just call it using the same hex code it had in it's function? Anyway it's indeed a great finding, I remember discarding a project because I didn't have a counter variable to iterate an array

 

Yes, you use the same reference as used in the defining function. Including the 00 local variable token.

 

johnnylump, idiot savant of x-com modding :smile:

 

Many (maybe most) great discoveries were made via accidents! Take your place amongst the greats :D

[anUser]

I've just thought that this trick can be used as a way to fake extra arguments for custom function calls, like firaxis did in BuildItems with that category variable... call me dumb, but I didn't thought of this at first and now it seems so great to me :)