Creating Singleton Objects using Visual C++

// Singleton.cpp : Defines the class behaviors for the application.
//

// This file is part of Singleton application to demonstrate the concept of Singleton classes.
// This file is generated by AppWizard and is provided "as is" with no expressed or 
// implied warranty.

#include "stdafx.h"
#include "Singleton.h"

#include "MainFrm.h"
#include "SingletonDoc.h"
#include "SingletonView.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////////
// CSingletonApp

BEGIN_MESSAGE_MAP(CSingletonApp, CWinApp)
	//{{AFX_MSG_MAP(CSingletonApp)
	ON_COMMAND(ID_APP_ABOUT, OnAppAbout)
		// NOTE - the ClassWizard will add and remove mapping macros here.
		//    DO NOT EDIT what you see in these blocks of generated code!
	//}}AFX_MSG_MAP
	// Standard file based document commands
	ON_COMMAND(ID_FILE_NEW, CWinApp::OnFileNew)
	ON_COMMAND(ID_FILE_OPEN, CWinApp::OnFileOpen)
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CSingletonApp construction

CSingletonApp::CSingletonApp()
{
	// Step 1 - Initialize message handler pointer
	m_pMsgHndlr		= NULL;
	m_csHndlrType	= _T("");
}

CSingletonApp::~CSingletonApp()
{
	// Step 1 - Delete message handler object
	delete m_pMsgHndlr;
}

/////////////////////////////////////////////////////////////////////////////
// The one and only CSingletonApp object

CSingletonApp theApp;


/////////////////////////////////////////////////////////////////////////////
// CSingletonApp initialization

BOOL CSingletonApp::InitInstance()
{
	// 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.

	LoadStdProfileSettings(0);  // 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.

	CSingleDocTemplate* pDocTemplate;
	pDocTemplate = new CSingleDocTemplate(
		IDR_MAINFRAME,
		RUNTIME_CLASS(CSingletonDoc),
		RUNTIME_CLASS(CMainFrame),       // main SDI frame window
		RUNTIME_CLASS(CSingletonView));
	AddDocTemplate(pDocTemplate);

	// Parse command line for standard shell commands, DDE, file open
	CCommandLineInfo cmdInfo;
	ParseCommandLine(cmdInfo);

	// Get message handler object, for the given key
	m_pMsgHndlr = CMsgHndlr::GetMsgHndlr( cmdInfo.m_strFileName );
	if( m_pMsgHndlr == NULL )
	{
		AfxMessageBox( CString( "Unable to get the message handler object for the key - \"" ) 
			+ cmdInfo.m_strFileName + CString( "\"." ) );
		return FALSE;
	}

	// Set handler type
	m_csHndlrType = cmdInfo.m_strFileName;
	if( m_csHndlrType.IsEmpty() )
	{
		m_csHndlrType = "<Default>";
	}

	// Set filename to empty and shell command to file new, to avoid open error
	cmdInfo.m_strFileName = _T("");
	cmdInfo.m_nShellCommand = CCommandLineInfo::FileNew;
	
	// Dispatch commands specified on the command line
	if (!ProcessShellCommand(cmdInfo))
		return FALSE;

	return TRUE;
}

/////////////////////////////////////////////////////////////////////////////
// CAboutDlg dialog used for App About

class CAboutDlg : public CDialog
{
public:
	CAboutDlg();

// Dialog Data
	//{{AFX_DATA(CAboutDlg)
	enum { IDD = IDD_ABOUTBOX };
	//}}AFX_DATA

	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CAboutDlg)
	protected:
	virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support
	//}}AFX_VIRTUAL

// Implementation
protected:
	//{{AFX_MSG(CAboutDlg)
		// No message handlers
	//}}AFX_MSG
	DECLARE_MESSAGE_MAP()
};

CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
	//{{AFX_DATA_INIT(CAboutDlg)
	//}}AFX_DATA_INIT
}

void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
	CDialog::DoDataExchange(pDX);
	//{{AFX_DATA_MAP(CAboutDlg)
	//}}AFX_DATA_MAP
}

BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
	//{{AFX_MSG_MAP(CAboutDlg)
		// No message handlers
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

// App command to run the dialog
void CSingletonApp::OnAppAbout()
{
	CAboutDlg aboutDlg;
	aboutDlg.DoModal();
}

/////////////////////////////////////////////////////////////////////////////
// CSingletonApp commands