The simplest message box is used to display a message to the user. This type of message box is equipped with only one button, labeled OK. Here is an example:

Figure 34: A Simple Message Box

A more elaborate or detailed message box can display an icon and/or can have more than one button:

1. Start Microsoft Visual Studio
2. On the main menu, click File -> New Project...
3. In the Project Types, click Visual C++
4. In the Templates list, click Win32 Project
5. Set the Name to Exercise2
6. Click OK
7. On the first page of the wizard, click Next
   
8. On the second page, accept Windows Application and click Empty Project
9. Click Finish
10. To make sure that this application uses MFC, on the main menu, click Project -> Properties...
11. In the left list, click Configuration Properties
12. In the right list, click User of MFC, click the arrow of its combo box and select Use MFC In A Shared DLL
13. Click OK
14. In the Solution Explorer, right-click Source Files, position the mouse on Add, and click New Item...
15. In the Templates lists click C++ File (.cpp)
16. Set the Name to Exercise
17. Click Add
18. In the empty document, type the following:
    

    #include <afxwin.h>
    
    class CExerciseApp : public CWinApp
    {
        BOOL InitInstance()
        {
    	return TRUE;
        }
    };
    
    CExerciseApp theApp;

19. Save the file
20. If the Resource View is not visible, on the main menu, click View -> Other Windows -> Resource View.
    In the Reource View, right-click Exercise1 -> Add -> Resource...
21. In the Add Resource dialog box, click String Table
     
    
22. Click New
23. Under the Type column header, click IDS_STRING101 and edit it to display IDS_ANNOUNCE and press Enter
24. To save, on the Standard toolbar, click the Save button
25. Close that window by clicking the Close button
26. In the Resource View, expand the Exercise1 node et notice the Exercise1.rc node

To create a message box, the Win32 library provides a global function called MessageBox. Its syntax is:

int MessageBox(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType);

If you want to use this version from Win32, because it is defined outside of MFC, you should start it with the scope access operator “::” as follows:

::MessageBox(. . .);

As we will see shortly, the Win32's MessageBox() function requires a handle (not necessarily difficult to provide but still). To make the creation of a message a little easier, the MFC library provides its own version of the MessageBox() function. Its syntax is:

int MessageBox(LPCTSTR lpszText,
	       LPCTSTR lpszCaption = NULL,
	       UINT nType = MB_OK);

To still make it easier, the MFC framework provides the AfxMessageBox function used to create a message box. Although this function is global, its scope is limited to MFC applications. This means that you can use the Win32's global MessageBox() function with any compiler used on the Microsoft Windows operating systems but you cannot use the MFC's global AfxMessageBox() function with any compiler other Visual C++. The AfxMessageBox() function is overloaded with two versions whose syntaxes are:

int AfxMessageBox(LPCTSTR lpszText,
		  UINT nType = MB_OK,
		  UINT nIDHelp = 0);
int AFXAPI AfxMessageBox(UINT nIDPrompt,
			 UINT nType = MB_OK,
			 UINT nIDHelp = (UINT) -1);

Based on the above functions, a message box can be illustrated as follows:

As seen above, you have the choice among three functions to create a message. There is no valid reason that makes one of them better than the other. They do exactly the same thing. The choice will be based on your experience and other factors.

If you decide to use the Win32's MessageBox() function, you must specify the handle to the application that created the message box. As we will learn eventually when we study controls, you can get a handle to a (CWnd-derived) control with a call to m_hWnd. For example, if a button on a dialog box initiates the message box, you can start this function as follows:

::MessageBox(m_hWnd, …);

We also saw that you can get a pointer to the main window by calling the MFC's global AfxGetMainWnd() function. This function only points you to the application. To get a handle to the application, you can call the same m_hWnd member variable. In this case, the message box can be started with:

::MessageBox(AfxGetMainWnd()->m_hWnd, …);

If you are creating a message but do not want a particular window to own it, pass this hWnd argument as NULL.

If you decide to call the AfxMessageBox() function, as seen previously, you have two options. You can pass a string as argument. Here is an example:

AfxMessageBox(L"Welcome to Microsoft Foundation Class Library.");

An alternative is to pass a string identifier from a resource file.

1. In the Resource View, expand the String Table node and double-click the String Table file
2. Click under Caption (on the right side of 101) et type Make sure you fill out your time sheet before leaving
3. Click the Exercise.cpp tab and change the file as follows:

   #include <afxwin.h>
   #include "resource.h"
   
   class CExerciseApp : public CWinApp
   {
       BOOL InitInstance()
       {
   	AfxMessageBox(IDS_ANNOUNCE);
   	return TRUE;
       }
   };
   
   CExerciseApp theApp;

4. To execute the application, press Ctrl + F5
5. When asked to build, click Yes

For all the message box functions, the Text argument a null-terminated string. It specifies the text that would be displayed to the user. This argument is required. Here is an example that uses the MessageBox() function:

AfxMessageBox(L"The name you entered is not in our records");

If you want to display the message on various lines, you can separate sections with the new line character '\n'. Here is an example:

AfxMessageBox(L"If you think there is a mistake,\nplease contact Human Resources");

If the message you are creating is too long to fit on one line, you can separate lines by ending each with a double-quote and starting the next line with a new double-quote. As long as you have not closed the function, the string would be considered as one entity. You can also use string editing and formatting techniques to create a more elaborate message. This means that you can use functions of the C string library to create your message.

1. To create a message box, call the AfxMessageBox() function as follows:
   

   #include <afxwin.h>
   #include "resource.h"
   
   class CExerciseApp : public CWinApp
   {
       BOOL InitInstance()
       {
   	AfxMessageBox(L"The name you entered is not in our records.\n"
   		      L"If you think there is a mistake, please contact HR.\n"
   		      L"You can also send an email to humanres@functionx.com");
   
   	return TRUE;
       }
   };
   
   CExerciseApp theApp;

2. Press Ctrl + F5 to test the application and click Yes
   
   
3. Click OK to close the message box and return to your programming environment

The caption of the message box is the text that displays on its title bar. If you create a message box using the AfxMessageBox() function, it allows you to specify only one argument, namely the text to display to the user, which is the value of the Text argument. In this case, the title bar of the message box would display the name of the application that "owns" the message box.

If you want to display your own caption on the title bar, call the MessageBox() function. Specify the argument for the caption. The Caption argument is a null-terminated string that would display on the title bar of the message box. Here is an example:

MessageBox(NULL,
	     L"Due to an unknown internal error, this application will now close.",
	     L"Regular Warning", 0);

Although the Caption argument is optional in the MFC,s MessageBox() and the AfxMessageBox() functions, it is required for the Win32's MessageBox() function. Because it is in fact a pointer, you can pass it as NULL. Here is an example:

MessageBox(NULL,
	     L"Due to an unknown internal error, this application will now close.",
	     NULL, 0);

In this case, the title bar of the message box would display Error:

This caption may not be friendly on most applications and could appear frightening to the user. Therefore, unless you are in a hurry, you should strive to provide a friendly and more appropriate title.

1. To display a caption for the message box, change the MessageBox() call as follows:
   

   #include <afxwin.h>
   #include "resource.h"
   
   class CExerciseApp : public CWinApp
   {
       BOOL InitInstance()
       {
   	MessageBox(NULL,
   		L"The name you entered is not in our records.\n"
   		L"If you think there is a mistake, please contact HR.\n"
   		L"You can also send an email to humanres@functionx.com",
   		L"Failed Logon Attempt", 0);
   
   	return TRUE;
       }
   };
   
   CExerciseApp theApp;

2. Test the application
    
   
3. Return to your programming environment