VERY basic help with DLL needed

Hello.
I'm absolutely new to C++ and having some problems to create even the most somple program.
As I still write a kindoff big project in VB and there is no way for me to do this in C++ I thought it would be cool indeed to have a .dll written in C++ and cal it in VB.
(By the way I use Visual C++ 6)


So what I actually ask for, is as detailed help as possible whith that.

I thought about to start with a .dll (just so I can concentrate on the basics) that gets a number from VB, adds, lets say, the number 2 to this number and returns the new number.

Also I would be happy I someone would show how to call that dll from VB.
I know that is pretty much demanded (in fact it must seem that I ask you to write my programs) but I having a hard time with C++, and the tutorials I read so far left me wondering where actually to type the code... (well, it's not that bad but you get the point)

Your help is very much appreciated.

This is actually not that hard to do. There are many, many ways to acheive it though. Here (http://www.developerfusion.com/show/1973/)'s an example of one of the easiest.

Actually I found that tutorial too!
And it even works for me.
Just one problem. I think the code is dealing with to much stuff, I mean as I know nothing about C++ i found it hard to even edit the code. You know what i mean?

Anyway I wrote this in a *.cpp


#include "AddNumber.h"

long __stdcall Calculate (int &Number, int &Result)

{

Result = Number * Number;


return 0;

}

And I compiled it and there is no error.
When I call it whith VB though, the program just ends.
If I leave out the "Result = Number * Number;" part
there is no error.

Could you show what I have to do to actually return the result value to VB.
I think that I know how to give the number to the dll, at least i hope so.

(I ask for c++ code here)

Thank you!

What is the VB declaration you used for this function, and the VB
code you used to call it?

Private Declare Function Calculate Lib "c:\temp\addnumber.dll" (ByVal PutV As Integer, ByVal GetV As Integer) As Long



Private Sub Form_Load()

Dim RetVal As Long
Dim Number As Integer
Dim Result As Integer

Number = 20

RetVal = Calculate(Number, Result)
MsgBox (Result)

End Sub


I think that this is not the problem. I suspect that the error is in the C++ code. As I said, if I do not calculate anything in the dll. everything works (accept that nothing happens and the mssgbox shows 0)...
Thanks

The problem is the ByVal passing of parameters. There is no
way to pass the value back.

Oh, so the problem is the ByVal-thing. I understand.

...Or rather not.
Come on, I really appreciate a helping hand here.
Well...

When a variable is passed byval, the value is passed. When the
normal byref (default), the address of the variable is passed. Your
C function parameters are int &Number, int &Result, which would
be references to the variables, so it seems like you should be
passing byref. I am not at all sure about this though, but I am
sure if you want to modify the passed parameters, they have to
be passed byref.

Ha!
I wrote Byref in the VB-code and changed a small detail in the C++-code and now it works. thanks.

You also have to remember that an Integer in C++ is not the same as one in VB.
And Int in C++ is a Long in VB.
A Short in C++ is an Integer in VB.
So your also calling it with the wrong data types.
Why not just call it like this:

int _stdcall Calculate (int Number)
{
Return Number * Number;
}

This way, when you call Result= Calculate (Number) the result from the dll function will be returned in the variable Result.

#include "AddNumber.h"

long __stdcall Calculate (int &Number)

{

Number = Number * Number;


return 0;

}


My code is like this, and it works.
I don't know what the "&" in front of Number is good for though.
Also I don't know what return means...
I thought return 0 would just close the programm or so.
.... anyway. thanks

Pookie is correct, your VB declaration needs to be As Long.

Originally posted by B_old
I don't know what the "&" in front of Number is good for though.
Also I don't know what return means...
I thought return 0 would just close the programm or so.
.... anyway. thanks

The & in front of a Variable means the memory address of the variable which is being referenced to it. Which basically means the same as byref in VB, so whatever number the &number becomes, it will change the original VB variable which it was referenced with too as well.

The return command is a way to exit from the function, and putting a value allows you to return some data from the function.
So:

int _stdcall (int Number) {
if ( Number < 0) {
Number = -Number;
}
Return Number; // Absolute value of number
} // int means the variable type being returned from the function

If you don't wish to return anything from a function

void _stdcall (int Number) {
Return 0;
} // function returns nothing, or void.

btw, A faster method of making a negative int to positive is:
Number=( Number and 0x7FFFFFFF ); :)

Doing a search on the internet, I found this site for you which has some tutorials and articles aimed at beginners.

http://www.codeproject.com/cpp/#Beginners

Well, OK.
Thanks for the link to the beginners tutorial!.
Can you also return more then one value from a funtion?
Thanks for the help!

If you pass params ByRef, sure.