The return bug

[soulreaping]

I've seen in many sites and system that people say "the return bug".

I didn't really understand, what is the bug?

Thanks

 

[~GaLs~]

function H2I takes handle h returns integer
return h
return 0
endfunction

function func takes nothing returns nothing
local unit u
call BJDebugMsg(I2S(H2I(u)))
endfunction

 

[TheDamien]

function H2I takes handle h returns integer
    return h
    return 0
endfunction

There is a bug that allows you to return data of one type as though it were another. H2I is the most widely used example of the return bug - since a handle variable is actually a reference to an object, when you return it as an integer you get the object's location on the handle stack.

 

[Tom Jones]

The return bug is simply just that a function will return on the first return it meets. However it's more commonly used to describe this function:

function H2I takes handle h returns integer
    return h
    return 0
endfunction

As you see the function is actually not returning a integer, but a handle. Luckily handles are simply integer ids, so this doesn't crash the map due to bad type casting. It also work the other way around:

globals
    integer id
endglobals

function I2T takes integer id returns timer
    return id
    return null
endfunction

function ...
    local timer t = I2T(id)

    call TimerStart(t,1,false,null)
endfunction

function ...
    local timer t = CreateTimer()
    set id = H2I(t)
endfunction

This however will crash the map if you use a bad typecast, etc. unit to timer, or at least corrupt the handle stack.

Typecasting from handle to integer and the other way around, has been made obsolete when structs were introduced.