Topic: Passing multiple variables from VB.NET to C#

[gablackburn]

Long story short, a guy at my office wrote a complex routine in C++ which does a lot of calculations with 3D coordinates.  Another guy wrote a routine in C# to access the C++ .DLL and return some results.  Since VB.NET cannot use UNSAFE, I can't access the C++ .DLL.  However, C# can.  I'd like to be able to call the C# Class Library from VB.NET but I'm having problems getting C# to return more than one variable.

I've written some simplified code below, but if I can get this to work, then I'll be able to get his code to work.

To start off, I'm not all that familiar with C#, so take it easy on me.  This is the C# code I wrote to do the calculation...

Code: [Select]

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace nsClassLibrary
{
    public class VBSamples
    {
        public double RetOneDouble(double GetDouble)
        {
            double dbl = GetDouble + 11;
            return dbl;
        }
    }
}
In VB.NET, after referencing the C# .DLL, I can use this code to call the C# Class Library to return one variable .

Code: [Select]

Public Class Form1
    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim obj As New nsClassLibrary.VBSamples
        MessageBox.Show(obj.RetOneDouble(22))
        Me.Close()
    End Sub
End Class

The problem comes when I pass two or more doubles/variables, C# it handles it fine, but it cannot return both values back to VB.



So I feel like a STRUCT may work for me, I just can't get it to work I'm obviously doing something wrong when setting this up, again, I'm not familiar with C#.

Code: [Select]

    struct struTwoDoubles
    {
        public double GetDbl1, GetDbl2;
    }
But I haven't had any luck with it...

Code: [Select]

        private struTwoDoubles foo(double dbl1, double dbl2)
        {
            struTwoDoubles abc = new struTwoDoubles();
            abc.GetDbl1 = dbl1 * 2;
            abc.GetDbl2 = dbl2 * 3;
            return (abc.GetDbl1,abc.GetDbl2);
        }
I'm not sure what else to try here and I feel I've done a lot of Googling in the last few days, but this isn't addressed much.

Any input will be helpful, thanks in advance.

GAB

[BlackBox]

Just a guess, but wouldn't an Overload (same Method, different parameters and return) work? 


Pseudo code:

Code - C#: [Select]

1. using System;
2. using System.Collections.Generic;
3. using System.Linq;
4. using System.Text;
5.  
6. namespace Foo
7. {
8.     public class Functions
9.     {
10.         public static double myFunction(double num)
11.         {
12.             double dbl = num + 11;
13.             return dbl;
14.         }
15.  
16.         public static List<double> myFunction(double num1, double num2)
17.         {
18.             double dbl1 = num1 * 2;
19.             double dbl2 = num2 * 2;
20.             List<double> result = new List<double>;
21.             result.Add(dbl1);
22.             result.Add(dbl2);
23.             return result;
24.         }
25.     }
26.  
27.     public class Samples
28.     {
29.         public void Foo()
30.         {
31.             List<double> foo = Functions.myFunction(22, 10);
32.         }
33.     }
34. }
35.  

[Kerry]

< .. >
The problem comes when I pass two or more doubles/variables, C# it handles it fine, but it cannot return both values back to VB.

< .. >

c# and VB.Net will only return one output value.
Some options to handle multiple values include ;

 •Use resultbuffer
 •Use output parameters (using the out or ref keywords)
 •Return an array
 •Return a structure that contains multiple members
 •Return an instance of a class
 •Use a dictionary or key-value pair or tuple as output

[It's Alive!]

how about pasing the arguments by reference?

[Kerry]

how about pasing the arguments by reference?

Yep

•Use output parameters (using the out or ref keywords)

[Jeff H]

But I haven't had any luck with it...

Code: [Select]

        private struTwoDoubles foo(double dbl1, double dbl2)
        {
            struTwoDoubles abc = new struTwoDoubles();
            abc.GetDbl1 = dbl1 * 2;
            abc.GetDbl2 = dbl2 * 3;
            return (abc.GetDbl1,abc.GetDbl2);
        }

You probably will not have much luck trying to return 2 doubles when the function signature defines returning a struTwoDoubles type.
 
Also if your trying to call the function from another assembly it will need to be visible. Your function is marked as private.
 
 
A little console app how to return your struct

Code - C#: [Select]

1.  
2.      class Program
3.     {
4.         static void Main(string[] args)
5.         {
6.             struTwoDoubles stw = foo(56.5, 45.6);
7.             Console.WriteLine(stw.GetDbl1);
8.             Console.WriteLine(stw.GetDbl2);
9.             Console.ReadLine();
10.         }
11.  
12.         private static struTwoDoubles foo(double dbl1, double dbl2)
13.         {
14.             struTwoDoubles abc = new struTwoDoubles();
15.             abc.GetDbl1 = dbl1 * 2;
16.             abc.GetDbl2 = dbl2 * 3;
17.             return abc;
18.         }
19.     }
20.     struct struTwoDoubles
21.     {
22.         public double GetDbl1, GetDbl2;
23.     }
24. }
25.  

[gablackburn]

Thanks everyone who commented.  I got some help from the C# guy and he was able to modify his code. 

[It's Alive!]

how about pasing the arguments by reference?

Yep

•Use output parameters (using the out or ref keywords)

DOH! 

[Kerry]

It's cool Daniel

My rule say we're allowed 5 oopsies a day ( accumulative).

ie

Code - C#: [Select]

1. var days     = 51;
2. var oopsies  = 254;
3. var proceed  = oopsies % (days * 5) > 0;
4.  
5. print (proceed);
6.  

[Keith™]

The proper ways to return multiple values from any function were covered in Kerry's first post.

If you examine exported functions, for example in the windows API, reference variables and structs tend to be the most common method to get alot of information from a single function, although there are many functions that return bitwise values allowing more than one bit of information (predefined information) to be transmitted between functions.

[gile]

Hi,

Another way if you target the Framework 4, is to return a Tuple.

[Jeff H]

Hi,

Another way if you target the Framework 4, is to return a Tuple.

•Use a dictionary or key-value pair or tuple as output

DOH! #2