Delphi-NULL终止字符

我有一个用于POS系统的极点显示产品，我想在屏幕上显示一些数据。我有一个C代码可以做到这一点，而且它运行良好C代码：

// demo.cpp : Defines the entry point for the console application.
//
#include <stdio.h>
#include <time.h>
#include <iostream>
using namespace std;

#include "windows.h"
int __cdecl main(int argc, char* argv[])
{
char in;
HMODULE hm;
long (*ou)();
long (*cu)();
long (*wp)(char*,long);
long (*ps)();
time_t tm;
char ss[64];
SetLastError( 0);
hm = LoadLibrary( "usbpd.dll");
printf( " hm = %p, %lu n",hm,GetLastError());
if ( hm==NULL ) return 1;
SetLastError( 0);
ou = (long(*)()) GetProcAddress( hm,"OpenUSBpd");
printf( " ou = %p, %lu n",ou,GetLastError());
SetLastError( 0);
cu = (long(*)()) GetProcAddress( hm,"CloseUSBpd");
printf( " cu = %p, %lu n",cu,GetLastError());
SetLastError( 0);
wp = (long(*)(char*,long)) GetProcAddress( hm,"WritePD");
printf( " wp = %p, %lu n",wp,GetLastError());
SetLastError( 0);
ps = (long(*)()) GetProcAddress( hm,"PdState");
printf( " ps = %p, %lu n",ps,GetLastError());
printf( " OpenUSB = %ld n", ou());

wp("Price: 5.00         ", 20);
wp("Total: 33.00        ", 20);
//for (long i=0;i<3;++i)
//  {
//  printf( " ps(1) = %ld n", ps());
//  time( &tm);
//  sprintf( ss,"x1bx40%s",ctime( &tm));
//  wp( ss, strlen( ss));
//  if ( argc>1 ) for (int j=30;j<255;++j) { ss[0] = j; ss[1] = 0; wp( ss,1);}
//  printf( " ps(2) = %ld n", ps());
//  }
printf( " CloseUSB = %ld n", cu());
cin.get();
FreeLibrary( hm);
return 0;
}

我有一个用Borland Delphi编写的代码来做与C代码相同的事情，但在显示我的数据后，它显示了一个垃圾字符。

Delphi代码：

unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TDLLFunc = function(): Integer;
ptr = ^TChar;
TChar = array[1..20] of PChar;
TDLLWriteFunc = function(ps_Text: ptr; pi_Length: Integer): Integer;
TForm1 = class(TForm)
  Button1: TButton;
  Button2: TButton;
  Edit1: TEdit;
  Button3: TButton;
  procedure Button3Click(Sender: TObject);
private
  { Private declarations }
public
  { Public declarations }
  h: THandle;
  OpenUSBpd : TDLLFunc;
  CloseUSBpd: TDLLFunc;
  WritePD   : TDLLWriteFunc;
  PdState   : TDLLFunc;
end;
var
  Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button3Click(Sender: TObject);
var xx: TChar;
  pxx: ptr;
  i: Integer;
begin
  h:= LoadLibrary('D:GlassTechTaboonDevicesPD23_26UUSBPD.DLL');
  if(h <> 0)then
    begin
      @OpenUSBpd := GetProcAddress(h, 'OpenUSBpd');
      @CloseUSBpd:= GetProcAddress(h, 'CloseUSBpd');
      @WritePD   := GetProcAddress(h, 'WritePD');
      @PdState   := GetProcAddress(h, 'PdState');
      OpenUSBpd;
    end;
  xx[1] := 'A';
  xx[2] := 'B';
  xx[3] := 'C';
  xx[4] := 'D';
  xx[5] := 'E';
  xx[6] := 'F';
  xx[7] := 'G';
  xx[8] := 'H';
  xx[9] := 'I';
  xx[10]:= 'J';
  xx[11]:= 'K';
  xx[12]:= 'L';
  xx[13]:= 'M';
  xx[14]:= 'N';
  xx[15]:= 'O';
  xx[16]:= 'P';
  xx[17]:= 'Q';
  xx[18]:= 'R';
  xx[19]:= 'S';
  xx[20]:= 'T';
  pxx:= @xx;
  WritePD(pxx, 0);
  CloseUSBpd;
end;
end.

请帮忙，谢谢