How to use delphi dll in C#?

Question

I tried to call a dll that is coded in delphi in C#. (delphi 11 64bit) I believe there will be some problems. Therefore, I tried some example in these website: Calling a Delphi method in a dll from c# Calling a Delphi DLL from a C# .NET application

But there is no response, and the applicaiton closes.

These are my codes:

example 1

delphi

function DBConnect1(inputStr,connStr:PWideChar):PWideChar;stdcall;
begin
  try
     result:=PWideChar('Hello from Delphi!');
  except
     result:=PWideChar('Exception');
  end;
end;

C#

[DllImport("Project1.dll",
    CallingConvention = CallingConvention.StdCall,
    CharSet = CharSet.Unicode)]
[return: MarshalAs(UnmanagedType.LPWStr)]
public static extern string DBConnect1(string inputString, string connectionString);

string inputString = "Parker";
string connectionString = "MyComputer";
string dbStrObj1 = DBConnect1(inputString, connectionString);
MessageBox.Show(dbStrObj1);

example 2

delphi

function Test1(sFD,sVD,sINI,sCh,sSD: string): PWideChar;stdcall;
var
  tempStr:string;
  str:WideString;
begin
  tempStr:=sFD+sVD+sINI+sCh+sSD;
  try
   result:= PWideChar(tempStr);
  except
    str:='Error';
    result:=PWideChar(str);
  end;
    result:=PWideChar(str);
end;

C#

[DllImport("Project1.dll", EntryPoint = "LoginLic", CharSet = CharSet.Unicode, CallingConvention = CallingConvention.StdCall)]
[return: MarshalAs(UnmanagedType.LPWStr)]
public static extern string LoginLic(string s1, string s2, string s3, string s4, string s5);

string strId = "PCMS";
string strVersion = "AD19";
string strIni = @"";
string strCheck = "0";
string strSubDate = null;
string aa;
aa = UseDll.LoginLic(strId, strVersion, strIni, strCheck, strSubDate);

Answer 1

You have to marshall function parameters also. Refer this link for passing string with Marshalling https://learn.microsoft.com/en-us/dotnet/framework/interop/default-marshalling-for-strings

[DllImport("Project1.dll",CallingConvention = CallingConvention.StdCall,CharSet = CharSet.Unicode)]
[return: MarshalAs(UnmanagedType.LPWStr)]
public static extern string DBConnect1(MarshalAs(UnmanagedType.LPWStr)]string inputString, MarshalAs(UnmanagedType.LPWStr)] string connectionString);