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Login Dialog Box 
 
Members Login

Introduction

A login dialog box is an object that is presented to a user to be authenticated in order to have access to a file, to a file, to a web page, to a web site, or to an application, etc. As always, there are various techniques this can be implemented and each programming or development environment provides its own set of options. Most of the time, regardless of the environment you are using, you would need a list that holds the members or users credentials. This list would contain usernames and passwords against which the user's credentials would be compared.

To implement the possibility of login, you should first decide how the list of credentials would be created or maintained. You can create a scenario in which the user would enter a username and a password before clicking a button to validate the values. If the user cannot be authenticated, you may present an option to send an email for a new account to be created. You can also allow the user to create a new account to update the list.
 

Visual C++ and Login

Like most other programming environments, to create a login process in an MFC application, you can use one of the approaches used for file processing. Optionally, and as we will do here, you can use the C' FILE class to open or save the list.

 

Practical Learning: Creating XML Attributes
  1. If you want to follow, create a new MFC Application named Corporate and accept all options, that is, click Finish on the wizard
  2. Using the Add Resource (Project -> Add Resource...) dialog box, add a new Dialog
  3. Change its ID to IDD_LOGIN_DLG and its Caption to Members Login
  4. Design the dialog as follows:
     
    Login Dialog Box Design
    Control ID Caption Other Properties
    Static Text   Username  
    Edit Control IDC_USERNAME    
    Static Text   Password  
    Edit Control IDC_PASSWORD   Password: True
    Button IDC_NEWACCOUNT_BTN Create New Account Multiline: True
  5. Add a new class for the dialog box and save it as CLoginDlg. Make sure the class is based on CDialog
     
  6. Add the following variables associated to the controls:
     
    ID Control Variable Value Variable
      Type Name Type Name
    IDC_USERNAME CEdit m_EditUsername    
    IDC_USERNAME     CString m_Username
    IDC_PASSWORD     CString m_Password
  7. Using the Add Resource dialog box, add a new Dialog
  8. Change its ID to IDD_NEWACCOUNT_DLG and its Caption to New Account Creation
  9. Design the dialog as follows:
     
    Login Dialog Box - Design
    Control ID Caption Other Properties
    Static Text   Username  
    Edit Control IDC_USERNAME    
    Static Text   Password  
    Edit Control IDC_PASSWORD   Password: True
    Static Text   Confirm Password  
    Edit Control IDC_CONFIRM_PASSWORD   Password: True
    Button IDOK Submit  
  10. Add a new class for the dialog box and save it as CNewAccountDlg. Make sure the class is based on CDialog
  11. Add the following variables associated to the controls:
     
    ID Control Variable Value Variable
      Type Name Type Name
    IDC_USERNAME CEdit m_EditUsername    
    IDC_USERNAME     CString m_Username
    IDC_PASSWORD CEdit m_EditPassword    
    IDC_PASSWORD     CString m_Password
    IDC_CONFIRM_PASSWORD     CString m_ConfirmPassword
  12. While still in the second dialog box, double-click the Submit button and implement its event as follows:
      
    void CNewAccountDlg::OnBnClickedOk()
{
	// TODO: Add your control notification handler code here
	UpdateData();

	// Make sure the user provided a username
	if( m_Username == "" )
	{
		AfxMessageBox("You must provide a username");
		m_EditUsername.SetFocus();
		return;
	}

	// Don't allow a blank password
	if( m_Password == "" )
	{
		AfxMessageBox("Blank passwords are not allowed\n"
					  "Please provide a password");
		m_EditPassword.SetFocus();
		return;
	}

	// The password and the blank password must be the same
	if( m_ConfirmPassword != m_Password )
	{
		AfxMessageBox("The passwords you provided are not the same");
		m_EditPassword.SetFocus();
		return;
	}

	FILE *fleCredentials;

	try {
		// Create a new file or open the existing one
		fleCredentials = fopen("credentials.crd", "a+");
		// Add the username to the file
		fprintf(fleCredentials, "%s ",  (LPCTSTR)m_Username);
		// Add the password to the file
		fprintf(fleCredentials, "%s\n", (LPCTSTR)m_Password);

		// After using it, close the file
		fclose(fleCredentials);
	}
	catch(...)
	{
		// Did something go wrong???
		AfxMessageBox("Could not validate the credentials");
	}

	UpdateData(FALSE);
	OnOK();
}
  13. Display the first dialog box, double-click its Create New Account button and implement its event as follows:
      
    // LoginDlg.cpp : implementation file
//

#include "stdafx.h"
#include "Corporate.h"
#include "LoginDlg.h"
#include ".\logindlg.h"

#include "NewAccountDlg.h"

// CLoginDlg dialog

IMPLEMENT_DYNAMIC(CLoginDlg, CDialog)
CLoginDlg::CLoginDlg(CWnd* pParent /*=NULL*/)
	: CDialog(CLoginDlg::IDD, pParent)
	, m_Username(_T(""))
	, m_Password(_T(""))
{
}

. . .


void CLoginDlg::OnBnClickedNewaccountBtn()
{
	// TODO: Add your control notification handler code here
	CNewAccountDlg Dlg;

	Dlg.DoModal();
}
  14. Double-click the OK button and implement its event as follows:
      
    void CLoginDlg::OnBnClickedOk()
{
	// TODO: Add your control notification handler code here
	UpdateData();

	char UsernameFromFile[20], PasswordFromFile[20];
	FILE *fleCredentials;
	bool ValidLogin = false;

	if( m_Username == "" )
	{
		AfxMessageBox("You must provide a username and a password or click Cancel");
		return;
	}
	if( m_Password == "" )
	{
		AfxMessageBox("Invalid Login");
		return;
	}

	try {
		// Open the file for reading
		fleCredentials = fopen("credentials.crd", "r");

		// Scan the file from beginning to end
		while( !feof(fleCredentials) )
		{
			// Read a username
			fscanf(fleCredentials, "%s", UsernameFromFile);

			// Compare the typed username with the username from the file
			if( strcmp((LPCTSTR)m_Username, UsernameFromFile) == 0 )
			{
				// With the current username, retrieve the corresponding password
				fscanf(fleCredentials, "%s", PasswordFromFile);
			
				// Compare the typed password with the one on file
				if( strcmp((LPCTSTR)m_Password, PasswordFromFile) == 0 )
				{
					ValidLogin = true;
				}
				else
					ValidLogin = false;
			}
		}
		if( ValidLogin == true )
			OnOK();
		else
		{
			AfxMessageBox("Invalid Credentials. Please try again");
			this->m_EditUsername.SetFocus();
		}

		fclose(fleCredentials);
	}
	catch(...)
	{
		AfxMessageBox("Could not validate the credentials");
	}
	
	UpdateData(FALSE);
}
  15. In the Solution Explorer, double-click the Corporate.cpp file and change its InitInstance() event as follows:
      
    // Corporate.cpp : Defines the class behaviors for the application.
//

#include "stdafx.h"
#include "Corporate.h"
#include "MainFrm.h"

#include "ChildFrm.h"
#include "CorporateDoc.h"
#include "CorporateView.h"

#include "LoginDlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif


// CCorporateApp

BEGIN_MESSAGE_MAP(CCorporateApp, CWinApp)
	ON_COMMAND(ID_APP_ABOUT, OnAppAbout)
	// Standard file based document commands
	ON_COMMAND(ID_FILE_NEW, CWinApp::OnFileNew)
	ON_COMMAND(ID_FILE_OPEN, CWinApp::OnFileOpen)
	// Standard print setup command
	ON_COMMAND(ID_FILE_PRINT_SETUP, CWinApp::OnFilePrintSetup)
END_MESSAGE_MAP()


// CCorporateApp construction

CCorporateApp::CCorporateApp()
{
	// TODO: add construction code here,
	// Place all significant initialization in InitInstance
}


// The one and only CCorporateApp object

CCorporateApp theApp;

// CCorporateApp initialization

BOOL CCorporateApp::InitInstance()
{
	// InitCommonControls() is required on Windows XP if an application
	// manifest specifies use of ComCtl32.dll version 6 or later to enable
	// visual styles.  Otherwise, any window creation will fail.
	InitCommonControls();

	CWinApp::InitInstance();

	// Initialize OLE libraries
	if (!AfxOleInit())
	{
		AfxMessageBox(IDP_OLE_INIT_FAILED);
		return FALSE;
	}
	AfxEnableControlContainer();
	// Standard initialization
	// If you are not using these features and wish to reduce the size
	// of your final executable, you should remove from the following
	// the specific initialization routines you do not need
	// Change the registry key under which our settings are stored
	// TODO: You should modify this string to be something appropriate
	// such as the name of your company or organization
	SetRegistryKey(_T("Local AppWizard-Generated Applications"));
	LoadStdProfileSettings(4);  // Load standard INI file options (including MRU)
	// Register the application's document templates.  Document templates
	//  serve as the connection between documents, frame windows and views
	CMultiDocTemplate* pDocTemplate;
	pDocTemplate = new CMultiDocTemplate(IDR_CorporateTYPE,
		RUNTIME_CLASS(CCorporateDoc),
		RUNTIME_CLASS(CChildFrame), // custom MDI child frame
		RUNTIME_CLASS(CCorporateView));
	if (!pDocTemplate)
		return FALSE;
	AddDocTemplate(pDocTemplate);
	
	// Prepare to display the Login dialog box
	CLoginDlg Dlg;

	// Display the dialog box and find out if the user clicked OK
	if( Dlg.DoModal() == IDOK )
	{
		// create main MDI Frame window
		CMainFrame* pMainFrame = new CMainFrame;

		if (!pMainFrame || !pMainFrame->LoadFrame(IDR_MAINFRAME))
			return FALSE;

		m_pMainWnd = pMainFrame;

		// call DragAcceptFiles only if there's a suffix
		//  In an MDI app, this should occur immediately after setting m_pMainWnd
		// Parse command line for standard shell commands, DDE, file open
		CCommandLineInfo cmdInfo;
		ParseCommandLine(cmdInfo);
		// Dispatch commands specified on the command line.  Will return FALSE if
		// app was launched with /RegServer, /Register, /Unregserver or /Unregister.
		if (!ProcessShellCommand(cmdInfo))
			return FALSE;
		// The main window has been initialized, so show and update it
		pMainFrame->ShowWindow(m_nCmdShow);
		pMainFrame->UpdateWindow();
	}

	return TRUE;
}
  16. Execute the application. Make sure you create an account first
 
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