AutoHotkey Community

The message box in the function displays the correct values, but i try to do the same thing outside the function and its coming up empty. Not sure what im doing wrong. Thanks

I changed the function to MakeNode(Left,Right,value, ByRef temp2) and that worked, though I don't understand why it doesn't work as a return value. If any one can explain why it would satisfy my curiosity

Are you familiar with AHK's rules for global variables?

You use the variable Len inside the function and outside the function. But these are two separate and different variables.

Since you do not define the variable inside the function as "Global", it is a local variable when used in the function and a global variable when used outside the function.

I'm not sure if this is your problem or not. But if you don't know the rules concerning global variables, you really should read the section in the Help file on "Functions" and read about Global and Static and ByRef. They are all very important concepts.

I definitely understand variable scopes or I never would have tried the byref idea.

It seems to me that, if inside of a function I execute a "return x" statement, and then in a function call do y:= foo() , then y should equal x.

Can anyone just paste this code into an autohotkey script and run it and verify that parent is not equaling temp2 from the function? I've tried on two PCs and get the same results. I even tried using dereference operator on the return statement thinking maybe using varsetcapcity on temp2 forced it into a pointer or something. There has to be something simple i'm missing here.

You should get the following results (addresses of course wont be the same) (the only parts we care about are the shouldbe variables)

*** First MessageBox from inside function
This is what the temp2 variable looks like RAW:

Left:0x1d22e60 Right:0x1d22ea0 Value:this string will be stored in the parent node Len: 0x2d
ShouldbeLeft: 0x1d22e60 Shouldberight: 0x1d22ea0 ShouldbeLen: 0x2d

*** Second MessageBox in auto exec section, after function call
This is what the parent variable looks like RAW:

Left: Right: Value: Len:
ShouldbeLeft: Shouldberight: ShouldbeLen:

In fact, lets simplify the problem, and try the code below. same thing happening.

Functions can only return strings; they cannot handle binary values. Specifically, return temp2 will only return the portion of temp2 up to the first zero-byte. You could instead return the address of the variable (&temp2), but since it is a non-static local variable it will not be valid after the function returns. One way to work around this is to manually allocate memory:
Memory allocated by GlobalAlloc cannot be reclaimed until the application exits or you call GlobalFree:
There are alternatives to GlobalAlloc / GlobalFree:

• msvcrt\malloc / msvcrt\free
• HeapAlloc / HeapFree - used with HeapCreate or GetProcessHeap.
• VirtualAlloc / VirtualFree (these work with multiples of the system's page size, usually 4KB).