.NET Interop: Delphi for .NET Unmanaged Exports

There are times when you want to interop with .NET by write something in managed code and want to use it in native code but don't want to use COM Interop. A simple feature of Delphi for .NET is Unmanaged Exports. This allows you to export a function from an Assembly for use from native land. I know there have been a lot of articles about this over the years since Delphi for .NET was released but you can't have too many examples. So here is a simple example of creating an Unmanaged Export:

File | New | Delphi for .NET Projects | Library

Note: There are very few cases you want to use Library. Most of the time you want to use Package. Unmanaged Exports is one of the few reasons to use Library

Paste the following code into the .dpr file.

library netlib;

{$UNSAFECODE ON}

uses
  SysUtils,
  libunit in 'libunit.pas';

procedure Foo;
begin
  WriteLn('Foo');
end;

exports
  Foo;

end.

File | New | Delphi Projects | VCL Forms Application

Paste the following code into the .dpr file.

program app;

{$APPTYPE CONSOLE}

uses
  Windows;

type
  TFooProc = procedure; stdcall;

var
  FooProc: TFooProc;
  LibHandle: THandle;
begin
  LibHandle := LoadLibrary(PChar('netlib.dll'));
  if LibHandle <> 0 then
  begin
    try
      @FooProc := GetProcAddress(LibHandle, 'Foo');
      if @FooProc <> nil then
        FooProc;
    finally
      FreeLibrary(LibHandle);
    end;
  end;
end.

When you run app.exe it will load the assembly netlib.dll, get the address of the exported function Foo and invoke it where Foo will print out the string 'Foo'.