use a function in a dll

[granbapt]

Hello,

I'm french so I apologize in advance for my English...

I have made a dll which contain a function in C. This function takes four parameters and returns three results, this is done with pointers :

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I tested it with an application and it works.

And now I want to use it in Excel (the aim is that the user enters the four parameters in four cells and see the three results in three other cells) but I have never used VBA before. I tried several things but none of them works.

My last failed try looked like this :

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My main problems are :
-to know how to chose between a Function and a Sub (i think that a Function returns a result and a Sub don't)
-to know how to manage with the pointers
-to understand how to get back the three results (I tried to get back at least one in the previous example but ideally I would like to have the three "Aff_***")


If anybody can explain to me how to solve my problem or can give me some advice, that would help me a lot !

Thank you very much in advance

[tkowal]

I do not believe I can help you but possibly I can point you in the right direction.

A function can only return one variable. One way of returning multiple items is by defining a User Define Type.
eg.

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This type then could be pass to your function Myfunction (mycar)
The function would be defined

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In a sense this is a pseudo class... the other way would be changing your function to a class or object and the params would be properties and methods...

Hopefully this will encourage some new thoughts on your problem.

[granbapt]

Ok, thank you for this helpfull hint about how to return multiple values.

But I still have not solve the main problem which is :

How can I call my Sub (or Function) Aff_Gaz declared from the C-function A2_Aff_lineique ? I can't call it without an exit value !


eg, in :

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my problem is the line

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for several reasons :


1. in C the function is definied by

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so I can't have

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can I ?

2. in C, I have pointers on Aff_tot, Aff_02 and Aff_H20 but no value because the three of them are the results

Please, help me if you can or tell me if my question is not clear...

Thank you all

[tkowal]

Shows how to handle C structures passed as pointers

http://msdn.microsoft.com/en-us/library/bb687915.aspx

[granbapt]

Hello !

I have had some answers and progressed a little.

I tried another way to define my C-function :

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became

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and return 1 (only in order to make it easier to call in VBA, I don't know if it's a good idea but it's a try...)

My VBA code is now :

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But when I enter the four parameters in four cells and I make =Affaiblissement_Gaz(B2;B3;B4;B5) in the cell destinated to the result, Excel gives me #VALEUR! (#VALUE! in english I guess).


I have no error message, so I can't find what is wrong...can you ?
Thank you very much in advance for your help !

[romperstomper]

Can you try calling the function in VBA rather than from a cell as that would allow you to step through and perhaps get an error message.

[tkowal]

Thanks romperstomper for the support -- this is a bit out of my arena!

Granbapt, here is another link http://www.excelforum.com/excel-prog...ba-to-dll.html

It references wrapping your dll call in a function and as romper indicated would allow you to step and test your calls through the debugger....

[granbapt]

Thank you all, I've found the problem which was (as usual) not where I was looking, and now it works !!

Indeed, my export of the function from C-code to DLL was wrong.

To close the subject, and if you are interested, here is the way I've done for the VBA part of my question :
(I took back my C-function in the initial form : with the void type)

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