Delphi製DLLをC#から呼び出す

How to call Delphi DLL from C# Function with String on args

ここでは、String型を使うためのツッコミどころを紹介します。
参考URL
https://stackoverflow.com/questions/9349530/why-can-a-widestring-not-be-used-as-a-function-return-value-for-interop
https://stackoverflow.com/questions/16601423/calling-a-delphi-method-in-a-dll-from-c-sharp

【DELPHI】

library sample;
uses
  System.SysUtils,
  System.Hash,
  System.Classes;
 
{$R *.res}
function tosha2(val : WideString ): WideString; stdcall;
begin
 
Pointer(Result) := nil;
//Result := val;
  with  THashSHA2.Create(SHA384) do
    begin
      Update(val);
      Result := HashasString;
    end;
 
 
end;
exports
 tosha2;
begin
end.

文字列型の引数と戻り値はWideString型で定義します。
Resultは、一度nilを代入しておきます。

　»さらっと参考URLを読んでください。

【C#】

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
 
namespace learning
{
    public partial class Form1 : Form
    {
 
        [DllImport("sample.dll")]
        public static extern void tosha2([MarshalAs(UnmanagedType.BStr)] out string Result, [MarshalAs(UnmanagedType.BStr)] string val);
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            string str;
            tosha2(out str, textBox1.Text);
 
            textBox2.Text = str;
        }
    }
}