delphi 创建DLL文件 及其调用和注意事项

library ProjectPnr;

{ Important note about DLL memory management: ShareMem must be the
  first unit in your library's USES clause AND your project's (select
  Project-View Source) USES clause if your DLL exports any procedures or
  functions that pass strings as parameters or function results. This
  applies to all strings passed to and from your DLL--even those that
  are nested in records and classes. ShareMem is the interface unit to
  the BORLNDMM.DLL shared memory manager, which must be deployed along
  with your DLL. To avoid using BORLNDMM.DLL, pass string information
  using PChar or ShortString parameters. }

uses
  SysUtils,
  Classes,

//再在Uses下声明一个函数：
function Add(a, b: integer):integer; // 函数功能 实现a，b相加
begin
   result := a + b;   
end

exports add;  // 必须要有这句才能输出

begin 
end.

function apnr(a,b: integer):integer; external 'test.dll';

procedure TForm2.Button1Click(Sender: TObject);
begin
 ShowMessage(add(1, 2));     //3
end;

//dll里函数
function add(a, b: integer): string;
begin
  result := IntToStr(a + b);
end;