Microsoft KB Archive/193099

= FIX: The CDialog::Create function returns an incorrect value when a dialog box is created in Visual C++ =

Article ID: 193099

Article Last Modified on 8/7/2007

-

APPLIES TO

 Microsoft Foundation Class Library 4.2, when used with:  Microsoft Visual C++ 5.0 Professional Edition

 Microsoft Visual C++ 5.0 Enterprise Edition

 Microsoft Visual C++ 5.0 Learning Edition

 Microsoft Visual C++ 6.0 Enterprise Edition</li></ul>

 Microsoft Visual C++ 6.0 Professional Edition</li></ul>

 Microsoft Visual C++ 6.0 Standard Edition</li></ul> </li></ul>

-

<div class="notice_section">

This article was previously published under Q193099

<div class="symptoms_section">

SYMPTOMS
If a dialog box is created via the CDialog::Create call, and the dialog box's OnInitDialog (in response to WM_INITDIALOG message) ends the dialog box via EndDialog, the CDialog::Create function returns a non-zero value. The CDialog::Create in this case should return zero.

Because the dialog box was destroyed due to an EndDialog call in the dialog's OnInitDialog, CDialog::m_hWnd is NULL in this case.

<div class="cause_section">

CAUSE
An additional test was made in the WM_INITDIALOG code (at line 365 of Dlgcore.cpp), which leads to Create succeeding even if the window handle is NULL.

MFC code for Visual C++ 5.0:

BOOL CWnd::CreateDlgIndirect(LPCDLGTEMPLATE lpDialogTemplate,

CWnd* pParentWnd, HINSTANCE hInst)

{

// ...

if (hWnd == NULL) {        // ...         // .. dump some debug information return FALSE; }

ASSERT(hWnd == m_hWnd); return TRUE; } MFC code for Visual C++ 6.0: BOOL CWnd::CreateDlgIndirect(LPCDLGTEMPLATE lpDialogTemplate,

CWnd* pParentWnd, HINSTANCE hInst)

{

// ...     // Help with error diagnosis (only if WM_INITDIALOG didn't      // EndDialog) if (hWnd == NULL && (m_nFlags & WF_CONTINUEMODAL)) // <--- PROBLEM!!!

{        // ... dump some debug information. return FALSE; }

ASSERT(hWnd == m_hWnd); return TRUE;

}

<div class="resolution_section">

RESOLUTION
When calling CDialog::Create check both the return value of CDialog::Create, and the value of CDialog::m_hWnd. If CDialog::m_hWnd is NULL, then the dialog-box creation is unsuccessful.

<div class="status_section">

STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been fixed in the Visual Studio 6.0 Service Pack 1.

To obtain this service pack, please see:

http://msdn2.microsoft.com/en-us/vstudio/Aa718362.aspx

For more information on the Visual Studio 6.0 Service Pack 1, please see the following articles in the Microsoft Knowledge Base:

193009 INFO: Visual Studio 6.0 Service Pack 1 Readme

194022 Visual Studio 6.0 service packs, what, where, why

194295 How To Tell That a Visual Studio Service Pack Is Installed

<div class="moreinformation_section">

MORE INFORMATION
Modify the code for displaying the dialog box so it also checks against the CDialog::m_hWnd variable. For instance: // Create a modeless dialog box. In this example, m_pModeless is a  // member variable of type CModeless where CModeless is a CDialog- // derived class. IDD_MODELESS is the ID number of a dialog-box template // resource. m_pModeless = new CModeless; if (m_pModeless->Create(IDD_MODELESS, this) &&     ::IsWindow(m_pModeless->m_hWnd)) {     // ... succeeded in dialog-box creation. }  else {     // ... failed in dialog-box creation. }

Steps to Reproduce Behavior
<ol> Copy the MFC sample MODELESS from the MSDN CDs.</li> Use ClassWizard to add an OnInitDialog message handler (in response to WM_INITDIALOG message) to the CAdderDialog class. CAdderDialog is a CDialog-derived class.</li>  Call EndDialog in the CAdderDialog::OnInitDialog as follows: BOOL CAdderDialog::OnInitDialog {     CDialog::OnInitDialog;

// TODO: Add extra initialization here EndDialog(-1); return TRUE; // return TRUE unless you set the focus to a control // EXCEPTION: OCX Property Pages should return FALSE }                   </li> Select Win32 Release build from VC++'s Build\Set Active Configuration menu command.</li> Build and then run the MODELESS sample.</li> Click Add in the dialog box. The m_pModeless->Create call in Modeldlg.cpp file (at line 178) returns TRUE, in this case causing the Add button (for displaying the CAdderDialog modeless dialog box) to be disabled.</li></ol>

(c) Microsoft Corporation 1999, All Rights Reserved. Contributions by Yeong-Kah Tam, Microsoft Corporation.

Keywords: kbfunctions kbqfe kbbug kbdlg kbfix kbnoupdate kbvc600sp1fix kbvs600sp1fix KB193099

-

[mailto:TECHNET@MICROSOFT.COM Send feedback to Microsoft]

© Microsoft Corporation. All rights reserved.