Call Function off an extern DLL

Question

1.00/5 (1 vote)

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VS2010

I already know how to import a dll into my project but by manually reference im receiving errors like "entry point was not found"

I created the dll file called myDll the class is called myFunctions and a function called showResult() As String just for example:

myDll.dll which is located on C:\ for example

VB

Public Class myFunctions
  Public Function showResult() as string
  Return "HELLO WORLD"
  End Function
End Class

myApplication

VB

Public Class callExternDll
  <dllimport("c:\mydll.dll")>
  Public Shared Function showResult() As String
  End Function
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

MsgBox(showResult)

End Sub

I want to call the function so to receive "hello world"

Posted 15-Oct-12 5:35am

bEGI23

Updated 15-Oct-12 5:47am

Wes Aday

v2

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Comments

Kuthuparakkal 15-Oct-12 11:41am

do you have Sub Main in your program ? like this :
' Allow easy reference to the System namespace classes.
Imports System

' This module houses the application's entry point.
Public Module modmain
' Main is the application's entry point.
Sub Main()
' Write text to the console.
Console.WriteLine ("Hello World using Visual Basic!")
End Sub
End Module

[no name] 15-Oct-12 11:46am

No i havent because its a class library and not a module so i thought i dont have to write it, but as you can see above there is at least one Function which id called showResult() so this must be an entry point too or am i wrong? do i have to rename it into sub showResult???

Sergey Alexandrovich Kryukov 15-Oct-12 13:25pm

The question is: how about the first fragment, which you probably written to export? Is it written as native code, or CLI (using VB.NET)?
--SA

[no name] 15-Oct-12 13:36pm

i dont know i just created it using Class Library and builded it!

Sergey Alexandrovich Kryukov 15-Oct-12 14:06pm

If you don't know what are you using and what is your platform, learn it first, before doing any programming. Or don't program at all, as it's useless. Know what you do.
--SA

[no name] 15-Oct-12 15:58pm

Yes theres is much to learn, i should visite a programming school

Sergey Alexandrovich Kryukov 15-Oct-12 16:01pm

Well, you can school yourself, using books, articles and manuals, but it should really be a school, with a focus on fundamentals. I think this is what most decent developers did, and you can do, too.
--SA

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Sergey Alexandrovich Kryukov · Answer 1 · 2012-10-15T07:34:00

Please see my comment to the question. If myFunctions.showResult is also in the CLI code, written in VB.NET, you don't need P/Invoke to use it. P/Invoke is only used to use unmanaged code in .NET (or other CLI) assembly. If both pieces are .NET assemblies, you simply reference one by another and use it directly:
http://en.wikipedia.org/wiki/.NET_assembly[^],
http://msdn.microsoft.com/en-us/library/ms973231.aspx[^].

If you use unmanaged code in a .NET assembly, you really need to use P/Invoke. One thing you should check up is using right entry point name, calling conventions (which should be the same between different versions of Basic), etc. When you have a DLL, you can see its exports using some binary dump tool like "dumpbin.exe". Please see:
http://msdn.microsoft.com/en-us/library/aa446532.aspx[^].

If you need to learn P/Invoke, please see:
http://en.wikipedia.org/wiki/P/Invoke[^],
http://msdn.microsoft.com/library/en-us/vcmxspec/html/vcmg_PlatformInvocationServices.asp[^].

This CodeProject article can also be useful: Essential P/Invoke[^].

—SA