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<H1><A NAME="delphenc0">Calling delphi DLL from MS Visual C++</A></H1>
<p><i>From: raike@swdev.co.nz (Bill Raike)</i></p>
<p>First, you need to declare all the functions exported by your
Delphi DLL with the keywords export; stdcall;</p>
<p>Secondly, your VC++ header file should declare all the
functions as of type __declspec(dllexport) __stdcall (double
leading underscores, and should enclose the function prototypes
within extern "C" { ... } . (You can also use
__declspec(dllimport) instead...) For example:</p>
<hr>
<pre>extern "C" {
int __declspec(dllexport) __stdcall plusone(int);
}
</pre>
<hr>
<p>Thirdly, in VC++ the compiler does insist on decorating
__stcall function names, so your Delphi DLL has to export these
functions accordingly. The way to do it is to modify the Delphi
2.0 .DPR file for your DLL by modifying the names of all
functions as they appear in the exports clause. For example, if
you are exporting a function plusone(intval : Integer) you need
to include it in the .DPR file's exports clause as:</p>
<hr>
<pre> plusone name 'plusone@4'</pre>
<hr>
<p>The number following the @ symbol is the total length in bytes
of all the function's arguments. The simplest way to find out the
correct values is to try to link your VC++ program and inspect
the "unresolved external" linker errors that result.</p>
<p>FINALLY, you can easily create an import library using the LIB
utility supplied with VC++. To do it, you need to manually (!!)
create a .DEF file for your DLL, with an exports clause listing
the names and/or ordinals of all the functions the DLL exports.
The format of the .DEF file is simple:</p>
<hr>
<pre>library MYLIB
description 'My very own DLL'
exports
plusone@4
</pre>
<hr>
<p>Then you execute LIB from the DOS/Win95 command line,
supplying your .DEF file as a command-line parameter. For
example, LIB /DEF:MYDLL.DEF . You tell VC++ about your .LIB file
in the Build|Settings|Linker dialog.</p>
<p>Sample code follows:</p>
<hr>
<pre>*******MYDLLMU.PAS
unit MyDLLMU;
interface
function plusone(val : Integer) : Integer; export; stdcall;
procedure ChangeString(AString : PChar); export; stdcall;
implementation
uses
Dialogs,
SysUtils;
function plusone(val : Integer) : Integer;
begin
Result := val + 1;
end;
procedure ChangeString(AString : PChar);
begin
if AString = 'Hello' then
StrPCopy(AString, 'World');
end;
end.
</pre>
<hr>
<hr>
<pre>***********MYDLL.DPR
library mydll;
{ Important note about DLL memory management: ShareMem must be the
first unit in your library's USES clause AND your project's (select
View-Project 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 DELPHIMM.DLL shared memory manager, which must be deployed along
with your DLL. To avoid using DELPHIMM.DLL, pass string information
using PChar or ShortString parameters. }
uses
SysUtils,
Classes,
MyDLLMU in 'MyDLLMU.pas';
exports
plusone name 'plusone@4',
ChangeString name 'ChangeString@4';
begin
end.
</pre>
<hr>
<hr>
<pre> *************** MYDLL.DEF
; -----------------------------------------------------------------
; File name: MYDLL.DEF
; -----------------------------------------------------------------
LIBRARY MYDLL
DESCRIPTION 'Test Delphi DLL, static loading into VC++ app'
EXPORTS
plusone@4
</pre>
<hr>
<hr>
<pre>************** DLLTSTADlg.H
// DLLTSTADlg.h : header file
//
#define USELIB
#ifdef USELIB
extern "C" {
int __declspec(dllimport) __stdcall plusone(int);
}
#endif //USELIB
/////////////////////////////////////////////////////////////////////////////
// CDLLTSTADlg dialog
class CDLLTSTADlg : public CDialog
{
// Construction
public:
CDLLTSTADlg(CWnd* pParent = NULL); // standard constructor
~CDLLTSTADlg();
// Dialog Data
//{{AFX_DATA(CDLLTSTADlg)
enum { IDD = IDD_DLLTSTA_DIALOG };
CString m_sVal;
CString m_sStr;
//}}AFX_DATA
// ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CDLLTSTADlg)
protected:
virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support
//}}AFX_VIRTUAL
// Implementation
protected:
#ifndef USELIB
HINSTANCE hMyDLL;
FARPROC lpfnplusone;
typedef int (*pIIFUNC)(int);
pIIFUNC plusone;
#endif //USELIB
HICON m_hIcon;
// Generated message map functions
//{{AFX_MSG(CDLLTSTADlg)
virtual BOOL OnInitDialog();
afx_msg void OnPaint();
afx_msg HCURSOR OnQueryDragIcon();
afx_msg void OnBtnplusone();
afx_msg void OnBtnplusoneClick();
afx_msg void OnBtndostringClick();
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};
</pre>
<hr>
<hr>
<pre>************ DLLTSTADlg.CPP
// DLLTSTADlg.cpp : implementation file
//
#include "stdafx.h"
#include "DLLTSTA.h"
#include "DLLTSTADlg.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif
extern CDLLTSTAApp theApp;
/////////////////////////////////////////////////////////////////////////////
// CDLLTSTADlg dialog
CDLLTSTADlg::CDLLTSTADlg(CWnd* pParent /*=NULL*/)
: CDialog(CDLLTSTADlg::IDD, pParent)
{
//{{AFX_DATA_INIT(CDLLTSTADlg)
m_sVal = _T("1");
m_sStr = _T("Hello");
//}}AFX_DATA_INIT
// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
#ifndef USELIB
hMyDLL = LoadLibrary("C:\\delpwork\\MYDLL.DLL");
if(hMyDLL == NULL)
PostQuitMessage(1);
lpfnplusone = GetProcAddress(HMODULE(hMyDLL), "_plusone");
if(lpfnplusone == NULL)
PostQuitMessage(2);
plusone = pIIFUNC(lpfnplusone);
#endif //USELIB
}
CDLLTSTADlg::~CDLLTSTADlg()
{
#ifndef USELIB
if (hMyDLL != NULL)
FreeLibrary(hMyDLL);
#endif //USELIB
}
void CDLLTSTADlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
//{{AFX_DATA_MAP(CDLLTSTADlg)
DDX_Text(pDX, IDC_LBLINT, m_sVal);
DDX_Text(pDX, IDC_LBLSTRING, m_sStr);
//}}AFX_DATA_MAP
}
BEGIN_MESSAGE_MAP(CDLLTSTADlg, CDialog)
//{{AFX_MSG_MAP(CDLLTSTADlg)
ON_WM_PAINT()
ON_WM_QUERYDRAGICON()
ON_BN_CLICKED(IDC_BTNPLUSONE, OnBtnplusoneClick)
ON_BN_CLICKED(IDC_BTNDOSTRING, OnBtndostringClick)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()
/////////////////////////////////////////////////////////////////////////////
// CDLLTSTADlg message handlers
BOOL CDLLTSTADlg::OnInitDialog()
{
CDialog::OnInitDialog();
// Set the icon for this dialog. The framework does this automatically
// when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon
// TODO: Add extra initialization here
return TRUE; // return TRUE unless you set the focus to a control
}
// If you add a minimize button to your dialog, you will need the code below
// to draw the icon. For MFC applications using the document/view model,
// this is automatically done for you by the framework.
void CDLLTSTADlg::OnPaint()
{
if (IsIconic())
{
CPaintDC dc(this); // device context for painting
SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0);
// Center icon in client rectangle
int cxIcon = GetSystemMetrics(SM_CXICON);
int cyIcon = GetSystemMetrics(SM_CYICON);
CRect rect;
GetClientRect(&rect);
int x = (rect.Width() - cxIcon + 1) / 2;
int y = (rect.Height() - cyIcon + 1) / 2;
// Draw the icon
dc.DrawIcon(x, y, m_hIcon);
}
else
{
CDialog::OnPaint();
}
}
// The system calls this to obtain the cursor to display while the user drags
// the minimized window.
HCURSOR CDLLTSTADlg::OnQueryDragIcon()
{
return (HCURSOR) m_hIcon;
}
void CDLLTSTADlg::OnBtnplusoneClick()
{
int iTemp;
char sTemp[10];
iTemp = atoi(m_sVal);
iTemp = plusone(iTemp);
m_sVal = itoa(iTemp, sTemp, 10);
UpdateData(FALSE);
}
void CDLLTSTADlg::OnBtndostringClick()
{
UpdateData(FALSE);
}
</pre>
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