DllCall

[BlankMind]

I'm trying to make a DLL to use with DllCall. I'm using Dev-cpp. Here is the code:

#define EXPORT __declspec(dllexport)

#include <cstdlib>
#include <cstdio>

extern "C"
{
       EXPORT int teste(int argumento)
       {
              return 23;
       }
}

And a test script calling the function:

$retorno = DllCall ("functions.dll","int","teste","int",10)
If @error <> 0 Then
    MsgBox(0,"","Error:" & @CRLF & @error)
Else
    MsgBox(0,"",$retorno[0])
EndIf

It gives a "This program found a problem..." Windows screen.

If I call the function without any arguments:

$retorno = DllCall ("functions.dll","int","teste")

it works and returns the correct value.

What am I doing wrong when using arguments?

Thanks.

[ProgAndy]

possibly the compiler removes the argument when it is not used. Just try something like:

#define EXPORT __declspec(dllexport)

#include <cstdlib>
#include <cstdio>

extern "C"
{
       EXPORT int teste(int argumento)
       {
              argumento = argumento;
              return 23;
       }
}

Edited January 31, 2010 by ProgAndy

[danielkza]

@ProgAndy:

The programmer of a compiler that removes function parameters at will should be beaten to death.

[BlankMind]

possibly the compiler removes the argument when it is not used.

Nothing has changed. I've already tested the function actually using the argument.

[ProgAndy]

ah, i forgot. you are using extern C. So you have to use 'int:cdecl'. It is just strange that it works when you completely remove the param. That irritated me.

$retorno = DllCall ("functions.dll","int:cdecl","teste","int",10)

[BlankMind]

ah, i forgot. you are using extern C. So you have to use 'int:cdecl'. It is just strange that it works when you completely remove the param. That irritated me.

Worked great, thanks!

It's in the function documentation, I should read it more carefully next time.

[jchd]

It is just strange that it works when you completely remove the param. That irritated me.

Hi ProgAndy,

As I see it, in the case of parameterless functions the stack is essentially empty, hence the cleaning specification (cdecl/stdcall) being about the stack layout and who cleans it is irrelevant.

I won't dig into that, but isn't it the case that some compilers decorate function names differently depending on the calling convention? In whichcase, this wouldn't work with those compilers. Anyway, not declaring the correct calling convention is a perversion.

[monoceres]

ah, i forgot. you are using extern C. So you have to use 'int:cdecl'.

Just a quick correction, extern "C" prevents C++ name mangling, it has nothing to do with calling convention

If you leave out any calling convention from the declaration then the compiler will use the default one, which in most cases is cdecl.

[ProgAndy]

Just a quick correction, extern "C" prevents C++ name mangling, it has nothing to do with calling convention

If you leave out any calling convention from the declaration then the compiler will use the default one, which in most cases is cdecl.

I thought if nothing specified, the convention is stdcall when using c++ names and cdecl when using extern "C", but you can override this.

Hi ProgAndy,

As I see it, in the case of parameterless functions the stack is essentially empty, hence the cleaning specification (cdecl/stdcall) being about the stack layout and who cleans it is irrelevant.

I won't dig into that, but isn't it the case that some compilers decorate function names differently depending on the calling convention? In whichcase, this wouldn't work with those compilers. Anyway, not declaring the correct calling convention is a perversion.

Yeah, but i thought calling a function that has parameters would crash if no parametesr were specified. Ah, I see, when you don't use them it doesn't care whether they are given or not. Edited January 31, 2010 by ProgAndy

[jchd]

Just a little clarification, when I wrote "some compilers decorate function names differently depending on the calling convention" I was refering to the prefix (mostly _), not about name mangling C++ introduced, which is something completely different as Monoceres just pointed out.