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I write a code in Delphi to initiate the com port that connected to my device and I get an Error access violation at address 0x0000 the code I write is:

unit Test_Cam;

interface

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

type
  TByteArr = array of byte;
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    ComboBox1: TComboBox;



    procedure Button1Click(Sender: TObject);
    procedure Doconnect;
    procedure CamOpen;
    Function StrToByte(const Value: String): TByteArr;
  private
    { Private declarations }


  public
  published
    property ObjectMenuItem;
    { Public declarations }
  end;
  TconfigPort = record
    BaudRate:Integer; // baud rate
    ByteSize:Integer; // number of bits/byte, 4-8
    Parity:Integer; // 0-4=no,odd,even,mark,space
    StopBits:Integer; // 0,1,2 = 1, 1.5, 2
    fOutxCtsFlow:Integer; // CTS Flow Control
  end;

  TPROGRESS_FUNC = procedure (blocks_total,blocks_done:Integer) of Object;

var
  Form1: TForm1;

  Function MetrocomEnterImageUpl(nport:Integer):Boolean; external 'metrocom.dll';
  procedure MetrocomAcquireFullFrame(nport:Integer); external 'metrocom.dll';


  Function MetrocomUploadJpeg(nPort:Integer; PROGRESS_FUNC:Tprogress_func; szFileName:string; nSubsampling:integer):Boolean; external 'metrocom.dll';
  Function MetrocomExitImageUpl(nPort:Integer):Boolean; external 'metrocom.dll';
  Function MetrocomInitCommunication(nPort:Integer; COMMPORTCONFIG:TconfigPort):Boolean; external 'metrocom.dll';
  Function MetrocomEndCommunication(nPort:Integer):Boolean; external 'metrocom.dll';
  Function camSetImageCompression(cam_handle:Integer; quality:Integer; method:Integer):Integer; external 'Camlib.dll';
  Function camSetCenteredWOI(cam_handle:Integer;img_width:Integer;img_height:Integer):Integer; external 'Camlib.dll';
  Function camInit(dev_interface:Integer):Integer; external 'Camlib.dll';
  Function camOpenEx2(device_name:TByteArr;ctl_bus_name:Byte;Var p_dev_type:Integer; ctl_bus_type:integer; camera_type:integer;dev_bus_type:Integer):Integer; external 'Camlib.dll';
  Function camClose(cam_handle:Integer):Integer; external 'Camlib.dll';
  Function camFree:Integer; external 'Camlib.dll';
  Function camGetOperatingMode(cam_handle:Integer; var mode:Integer):Integer; external 'Camlib.dll';

var
  Config_port: TconfigPort;
  m_bConnect:Boolean = false;
  m_nPort,m_nInit,nPort,i,j,m_camHandle:integer;
  nDeviceType:Integer = 0;
  device_name:string;
  szDeviceName:TByteArr;

implementation

{$R *.dfm}

function TForm1.StrToByte(const Value: String): TByteArr;
var
    I: integer;
begin
    SetLength(Result, Length(Value));
    for I := 0 to Length(Value) - 1 do
        Result[I] := ord(Value[I + 1]) ;
end;

procedure Tform1.DoConnect;
begin
 m_nPort := StrToInt(ComboBox1.Text) - 1;
 Config_port.BaudRate := 9600;
 Config_port.ByteSize := 8;
 Config_port.Parity := 0;
 Config_port.StopBits := 0;
 m_bConnect := MetrocomInitCommunication(m_nPort , Config_port);
end;

procedure TForm1.CamOpen;
begin
 m_nInit := camInit(0);
 if m_nInit < 0  then
    ShowMessage('Fail to camInit.');
 nPort := m_nPort + 1;
 device_name := 'COM' + IntToStr(nPort) + ' baud=' + IntToStr(Config_port.BaudRate) + ' parity=' + IntToStr(Config_port.Parity) + ' data=' + IntToStr(Config_port.ByteSize) + ' stop=' + IntToStr(Config_port.StopBits);
 szDeviceName := strtobyte(device_name);
 for i := 0 to 4 do
  begin
   for j := 0 to 4 do
    begin
     m_camHandle := camOpenEx2(szDeviceName, 0 ,  nDeviceType, 0, 1, 0);
     if m_camHandle < 0 then break;
    end;
   if m_camHandle < 0 then break;
  end;

end;


procedure TForm1.Button1Click(Sender: TObject);
begin
 DoConnect;
 CamOpen;
 camSetImageCompression(m_camHandle, 30, 0);
 camSetCenteredWOI(m_camHandle, 500, 220);

end;

end.

and the documentation for the DLL file is:

MetrocomInitCommunication
Purpose:
Open the port for communication and set up the ports parameters. The communication parameters only
matter when a real COM port is used  for either USB or Bluetooth virtual COM ports these settings are
ignored.
C/C++:
BOOL MetrocomInitCommunication(int i_port, COMMPORTCONFIG * p_config);
Visual Basic:
Declare Function MetrocomInitCommunication Lib "metrocom.dll" _ 
    (ByVal i_port As Long, ByRef config As COMMPORTCONFIG) As Long 
Parameters:
i_port - [in] Communication port number (0 for COM1, 1 for COM2, etc.)
p_config - [in] Port configuration structure  this parameter sets baud rate and other port settings to be
used during normal communication (not during image upload)
Return value:
1 if the parameters were set successfully and the port was opened, 0 otherwise.
4

1 回答 1

3

导入函数的调用约定不正确。您没有指定调用约定，因此使用默认的注册约定。请查阅文档以了解使用了什么调用约定。您给出的 VB6 声明使用 stdcall，所以这就是我的钱所在。所有 VB6 导入都是标准调用。翻译标头时，始终确保正确指定调用约定

修复后，互操作会出现更多问题。对象的使用显然是错误的。C++ 库不会实现它。使用 Delphi 字符串也是错误的。字符串很可能作为 C 字符串传递，即指向以空字符结尾的字符数组的指针。并且结构可能会通过引用而不是值传递。

对于有问题的函数，C++ 声明清楚地表明该结构是通过引用传递的。

函数应该这样声明：

function MetrocomInitCommunication(
    nPort: Integer; 
    const config: TConfigPort
): BOOL; stdcall; external 'metrocom.dll';
于 2013-09-23T20:25:18.980 回答