Making a DLL

[TheMG]

Is there anything special I have to do to a code for it to work as a DLL? (Other than the -dll command line). If you specifically know how to make it work for a thing called Gamemaker then thatd help!

[Fragmeister]

To make a .dll, it's simple. All code must be contained in functions (or subs, but functions make more sense, as you can return values) Put all the sub/function declarations into a .bi file, so that you can #include it into your programs that use it. Here's an example:

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'test.bas (this is the dll and needs to be compiled with -dll)
#include once "test.bi"
function foo(bar) as integer export
    return bar*2
end function

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'test.bi (this is #included in your dll source as well as the program.
declare function foo alias "foo" (bar) as integer

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'tester.bas:  this is just to test the function
#include once "test.bi"
input bar
print foo(bar)
sleep

[TheMG]

Are you sure? Ill show you my code:

Add.bas

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#Include once "Add.bi"

Function AddIt(N1 as double, N2 as double) as double export

    Return N1+N2
 
End Function

Add.bi

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Declare Function AddIt Alias "AddIt" (N1 as double, N2 as double) as double

Is that all right?

EDIT

It compiles fine, but when I try to execute it Im given an 'error defining external function' (basicly it cant run it).

[VirusScanner]

Not sure, but try changing your function line to read

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function AddIt alias "AddIt"(N1 as double, N2 as double) as double export

make sure to compile with -dll.

[Fragmeister]

hmmm. I described it exactly as I remember doing it. I'll double-check. You might try VirusScanner's suggestion, I don't think that extra alias is necessary, but you never know!

[TheMG]

Well it works, but numbers/strings it returns are all scrambled.

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Function HelloWorld Cdecl Alias "HelloWorld" () As String Export
    
    Return "Hello World"
    
End Function

But the return is all scrambled when run?!

[Fragmeister]

maybe remove cdecl?

[TheMG]

Well first I just left it out, but what do I call it as? Becuase I can call as stdcall or cdecl. When i replace both with stdcall it dont work.

[cha0s]

huh, and when i try to compile a dll, i get this:

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D:\FREEBASIC\bin\win32\dlltool.exe: Syntax error in def file proc.def:0

i think i'll try getting cvs later...

[v1ctor]

That happens when no export function is defined, dlltool doesn't like that for some reason.

Dynamic strings (STRING) can't be used when making DLL's for other languages than FB, they know nothing about the FB STRING descriptor, you have to use ZSTRING's + pointers.

[TheMG]

Ahh yes that is a problem I am having. I have to use ZSTRING, but then it says it cant export fixed length strings. How can we fix this?

[tunginobi]

Ahh yes that is a problem I am having. I have to use ZSTRING, but then it says it cant export fixed length strings. How can we fix this?

Try using a ZSTRING PTR instead, and tell us how that pans out.

[TheMG]

So do I just set the function as ZString Pointer Export, ye? And then I use it as normal?

EDIT

I have this:

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Function SayHello Cdecl Alias "SayHello" () As ZString Pointer Export
    
    Dim RV as ZString*5 = "Hello"
    
    Return @RV
    
End Function

But it says my assignment of "Hello" to RV is a type mismatch. Is this even how Im supposed to do it?

EDIT

Also I am implementing peek, poke and varptr into another language (using a dll), but how do I make an argument, isntead of being set to the value of what it is, point to the value of what it is.

Say I had a function called RandomFunc1. It had one argument, a single. I do this:

RandomFunc1(MyVar)

How do I instead of the first argument being the value of MyVar, but be its location. Bear in mind this language Im porting to only has single and string.

[VirusScanner]

The only problem with that is you're returning a stack address that will be invalid after you exit. And you're not letting there be room for the NULL character at the end. Try this:

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function ReturnString cdecl alias "ReturnString" ( ) as zstring ptr export
    dim as zstring ptr sp
    sp = allocate( 6 )
    *sp = "Hello"
    return sp
end function

but that also means that the language you are returning a value from will have to clean that up by calling free (FB calls it deallocate).

I don't see much of a point using a language that has only 2 variable types though. I'd personally tell the author to implement more features.

[TheMG]

I have told the author (link's http://www.gamemaker.nl, its just a simple gamemaker). Ill go try those edits. BTW can the allocate be replaced by *6?