Dll 使用 PChar 参数的小例子

当用delphi开发的dll中有参数或返回值是字符串时，需要调用sharemem单元，且需要borlnmm.dll一起发布程序。用Pchar代替string是一个解决方案，只不过对pchar的使用要复杂一些：

Dll 文件:
--------------------------------------------------------------------------------
 
library Lib;

uses
  SysUtils, Classes;

{$R *.res}

procedure Test(p: PChar);
const
  Title = 'Title ';
var
  str: string;
begin
  str := p;
  StrCopy(p, Title);
  StrCat(p, PChar(str));
end;

exports Test;

begin
end.
--------------------------------------------------------------------------------
调用的代码文件:
--------------------------------------------------------------------------------
 
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  end;

var
 Form1: TForm1;

implementation

{$R *.dfm}

procedure Test(p: PChar); external 'Lib.dll';

var num: Integer;

procedure TForm1.Button1Click(Sender: TObject);
var
  p: PChar;
begin
  Inc(num);
  p := StrAlloc(255);
  StrCopy(p, PChar(IntToStr(num)));
  Test(p);
  Text := p;
  StrDispose(p);
end;

end.
--------------------------------------------------------------------------------
调用的窗体文件:
--------------------------------------------------------------------------------
 
object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 103
  ClientWidth = 173
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 48
    Top = 40
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 0
    OnClick = Button1Click
  end
end