Re: Problem in performance of calling a dialog in DLL(Windows programm

"Giovanni Dicanio" <>
Tue, 23 Jun 2009 21:58:39 +0200
"creative22" <> ha scritto nel messaggio


Could I ask you tell me what the problem is with this code?
Any help would be greatly appreciated,

In addition to other answers, I tried rewriting your code to try to show the
use of robust container classes like std::vector and CString class to store
I did some modifications to original code, e.g.:

* The 'buff' struct is not required at DLL interface, so I moved it away
from public DLL header and put it in private DLL implementation file

* I rewrote the 'buff' struct storing an array of CString's inside, instead
of the unique string with \0 termination of substrings plus explicit size
In this way you make the code simpler because you don't need complex and
error-prone parsing code.
Moreover, you make your life easier using robust container and string
classes instead of TCHAR* raw pointers.

* I rewrote the DLL import/export #define

* I tried to indent the code a bit better (I think that code indentation is
a very important point of quality code)

You can find the new project here:

The source (DlgInDLL.cpp) and header (DlgInDLL.h) files of the DLL are also
copied below.



// DlgInDLL.cpp

// Export from DLL
#define DLGINDLL_API __declspec(dllexport)

#include <windows.h> // Win32 SDK
#include <vector> // STL vector
#include <atlstr.h> // CString
#include "DlgInDLL.h" // DLL public header
#include "resource.h"

struct Buff
    // List of strings to fill the combobox with
    std::vector< CString > Strings;

    // The string chosen by the user
    CString UserChoice;

// DLL instance handle
static HINSTANCE g_hModule = NULL;

// DllMain
BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason,LPVOID lpvReserved)
    if (fdwReason == DLL_PROCESS_ATTACH)
        g_hModule = hinstDLL;

    return TRUE;

// Dialog-box procedure - handles messages
BOOL CALLBACK SecondDlgProc(HWND hwndDlg,
                             UINT message,
                             WPARAM wParam,
                             LPARAM lParam)
    // Store 'buf' parameter when WM_INITDIALOG is called.
    // This is used to exchange data with caller function.
    static Buff * buff = NULL;

    switch (message)
        // *** Dialog Initialization ***

        // Save buffer pointer
        buff = reinterpret_cast<Buff *>( lParam );

        // Clear contents of the combobox
  SendDlgItemMessage(hwndDlg, IDC_COMBO1, CB_RESETCONTENT, 0, 0);

        // Add strings to combobox
        for (size_t i = 0; i < buff->Strings.size(); i++)
                (LPARAM) buff->Strings[i].GetString()

        return TRUE;

        if ( LOWORD (wParam) == IDOK )
            // *** OK Button Pressed ***

            // Get current selection
            int index = (int) SendDlgItemMessage(hwndDlg, IDC_COMBO1,
            int length = (int) SendDlgItemMessage(hwndDlg, IDC_COMBO1,
CB_GETLBTEXTLEN, index, 0) + 1 ;
            if (length > 0)
                std::vector<TCHAR> readerName(length);
                SendDlgItemMessage(hwndDlg, IDC_COMBO1, CB_GETLBTEXT, index,
(LPARAM) (&readerName[0]) );

                // Store it in string class
                buff->UserChoice = &readerName[0];
                // Empty string
                buff->UserChoice = _T("");
            EndDialog( hwndDlg, TRUE );
         return TRUE ;
        else if ( LOWORD (wParam) == IDCANCEL )
            // *** Cancel Button Pressed ***

            EndDialog( hwndDlg, FALSE );
            return TRUE;

    return FALSE;

// Function exported by the DLL
DLGINDLL_API void WINAPI SecondFunction(void)
    // Create buff struct on the heap
    Buff * buff = new Buff();

    // Fill the list of strings
    buff->Strings.push_back(TEXT("ACS READER 0"));
    buff->Strings.push_back(TEXT("ACS READER 1"));
    buff->Strings.push_back(TEXT("ACS READER 2"));

    // Show the dialog-box
 if( DialogBoxParam(
        reinterpret_cast<LPARAM>(buff)) )
        // Show the selected string to the user
        CString msg;
        msg.Format(_T("The value of reader is %s."),
     MessageBox( NULL, msg, TEXT("Note"), MB_OK );
        MessageBox( NULL, TEXT("The Second Function Succeeded."), NULL,
     MessageBox( NULL, TEXT("The Second Function Failed."), NULL,

    // Delete Buff structure
    delete buff;
    buff = NULL;



// DlgInDLL.h

#ifndef DLGINDLL_H
#define DLGINDLL_H

#ifdef __cplusplus
extern "C" {

#define DLGINDLL_API __declspec(dllimport)
#endif /* DLGINDLL_API */

DLGINDLL_API void WINAPI SecondFunction(void);

#ifdef __cplusplus
}; /* extern C */

#endif /* DLGINDLL_H */


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