Simple DLL 1

[djjd47130]

I need an example to create a basic DLL called from C# with just one function with 4 parameters. The 4 parameters will be 2 string values, one integer, and one boolean, and will return a boolean result. I need just a simple example to code the DLL in Delphi and hopefully also an example how to call it from C#. Please keep it simple.


JD Solutions

 

[majlumbo]

library mydll;

uses
   SysUtils, Classes, etc...

{$R *.res}

function myfunction(s1, s2: PChar; I1: Integer; B1:  BOOL):  BOOL; stdcall;
var
   Sa, Sb:  String;
begin
   RESULT := FALSE;
   Sa := s1; //if you prefer to work with strings internally, simply assign S1 and S2 to strings
   Sb := s2; //if not, continue with S1, S2
   {...}
   IF (..) THEN
      RESULT := TRUE;
end;

exports
   myfunction;

begin

end.

What are the valid range of values for I1?
You may want to change it to:
BYTE: 0 to 255
WORD: 0 to 65535
LONGINT/INTEGER: -2,147,483,648 to 2,147,483,647
INT64: -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

You can try to use the native Delphi Boolean instead of BOOL, but you may have problems using the function from other languages, like C# as you mentioned.

The main problem with dll's created with delphi is passing strings to or from a dll. Since you are passing in two strings, notice the function is expecting two PChars.

As far as how you call it from C#, maybe someone else can assist there.

 

[djjd47130]

Thanks, that helped. DLL is going to be a mediator between my previously built delphi projects and a website built in ASP.NET in C#. I know nothing about C#, and that's another thing I will need to figure out. Most of my projects are in regular string, integer, etc. This would be my first DLL, as is also my first C# project. I will eventually make an API on both ends.

JD Solutions

 

[majlumbo]

When creating the DLL, you can pick a DLL as the type of project you are creating. That will get the structure of the DLL established automatically by delphi.

 

[djjd47130]

I got everything done and plugged in, but I'm getting an error here. Here's the details:

JDEncr.dll built in Delphi 7:

function CompareStrings(PlainText, EncryptedText: String;
  EncType: Integer; CaseSensitive: Bool): Bool; stdcall;

And at the end:

exports
   CompareStrings;

DLL works perfect when I call it from Delphi:

Declaration:

function CompareStrings(PlainText, EncryptedText: String;
  EncType: Integer; CaseSensitive: Bool):  Bool; stdcall;

Implementation:

function CompareStrings(PlainText, EncryptedText: String;
  EncType: Integer; CaseSensitive: Bool):  Bool;  external 'JDEncr';

Now I try to use the same DLL from ASP.NET 4.0 in C#:

    public class JDEncr
    {
        [DllImport("JDEncr.dll", CallingConvention = CallingConvention.StdCall, CharSet = CharSet.Ansi)]

        public static extern bool CompareStrings(String PlainText, String EncryptedText, int EncType, bool CaseSensitive);

    }

Then I use that function:

bool P = JDEncr.CompareStrings(pwd, drAuth["Password"].ToString(), 1, true);

However, I get the following error:


"Unable to load DLL 'JDEncr.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)"


What am I doing wrong here?

JD Solutions

 

[majlumbo]

Remember that the delphi STRING type is not equivalent to what other languages. That's why it needs to be declared as a PChar in the DLL, which is a pointer to a string.

function CompareStrings(PlainText, EncryptedText: PChar;
  EncType: Integer; CaseSensitive: Bool): Bool; stdcall;

That will require that in your delphi program you convert your string to a PChar before passing it in.

Not sure if that is the basis of your problem, but it may be.

 

[djjd47130]

Update: I finally got it working

The DLL had to be in the website's bin folder, not in the root folder.

Everything works perfectly, thank you!


JD Solutions

 

[djjd47130]

I also did have to change Delphi's String to PChar. I'm using it as a regular String in C# however.

JD Solutions

 

[djjd47130]

Ok, I have done quite a bit with making methods in this DLL to use in the C# Web Application, which works just fine. Now, I need to know how to create a simple Object in this DLL and use this object class in the C# Application. In other words, I have created the following object in this DLL:

  TTestObject = class(TObject)
    String1: PChar;
    String2: PChar;
    Int1: Integer;
    Int2: Integer;
    Bool1: Bool;
    Bool2: Bool;
  end;

Now, how do I use this object from the C# Application?

(Perhaps I should be posting this in another forum?)



JD Solutions

 

[whosrdaddy]

You can make an activeX library and that can be imported without any problem in other environments (like C#, C++, VB, ...)

/Daddy

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