When you're writing programs, there are many types of data and operations that you must use again and again. Sometimes you have to do something as simple as creating a portable integer data type. Other times you need to do something a little more complex, like extracting a word from a long word value or storing the position of the mouse pointer. As you might know, Windows itself defines many constants and variables that you can use in your programs to help write programs faster. Using these previously defined constants and macros make your programs more portable and more readable by other programmers. Besides the macros, global constants, and variables defined by Windows, MFC adds its own set. In the following tables, you'll get a look at the most important of these globally available constants, macros, and variables.
Because there are so many constants, macros, and globals, Visual C++ organizes its constants, macros, and globals into ten categories. Those categories are listed as follows. The following sections describe each of these categories and the symbols they define.
Because a typical Visual C++ application contains only one application object but many other objects created from other MFC classes, you frequently need to get information about the application in different places in a program. Visual C++ defines a set of global functions that return this information to any class in a program. These functions, which are listed in Table 23.1, can be called from anywhere within an MFC program. For example, you frequently need to get a pointer to an application's main window. The following function call accomplishes that task.
CWnd* pWnd = AfxGetMainWnd();
Table 23.1 Application Information and Management
Function | Description |
AfxBeginThread() | Creates a new thread. |
AfxEndThread() | Terminates a thread. |
AfxGetApp() | Gets the application's CWinApp pointer. |
AfxGetAppName() | Gets the application's name. |
AfxGetInstanceHandle() | Gets the application's instance handle, which is the instance from which the default resources were loaded. |
AfxGetMainWnd() | Gets a pointer to the application's main window. |
AfxGetResourceHandle() | Gets the application's resource handle. |
AfxGetThread() | Gets a pointer to a CWinThread object. |
AfxRegisterClass() | Registers a window class in an MFC DLL. |
AfxRegisterWndClass() | Registers a Windows window class in an MFC application. |
AfxSetResourceHandle() | Sets the instance handle that determines where to load the application's default resources. |
AfxSocketInit() | Initializes Windows Sockets. |
MFC defines a number of delimiters that ClassWizard uses to keep track of what it's doing, as well as to locate specific areas of source code. Although you'll rarely, if ever, use these macros yourself, you will see them embedded in your AppWizard applications, so you might like to know exactly what they do. Table 23.2 fills you in.
Table 23.2 ClassWizard Delimiters
Delimiter | Description |
AFX_DATA | Starts and ends member variable declarations in header files that are associated with dialog data exchange |
AFX_DATA_INIT | In a dialog class's constructor, starts and ends dialog data exchange variable initialization |
AFX_DATA_MAP | In a dialog class's DoDataExchange() function, starts and ends dialog data exchange function calls |
AFX_DISP | Starts and ends OLE Automation declarations in header files |
AFX_DISP_MAP | Starts and ends OLE Automation mapping in implementation files |
AFX_EVENT | Starts and ends OLE event declarations in header files |
AFX_EVENT_MAP | Starts and ends OLE events in implementation files |
AFX_FIELD | Starts and ends member variable declarations in header files that are associated with database record field exchange |
AFX_FIELD_INIT | In a record set class's constructor, starts and ends record field exchange member variable initialization |
AFX_FIELD_MAP | In a record set class's DoFieldExchange() function, starts and ends record field exchange function calls |
AFX_MSG | Starts and ends ClassWizard entries in header files for classes that use message maps |
AFX_MSG_MAP | Starts and ends message map entries. |
AFX_VIRTUAL | Starts and ends virtual function overrides in header files |
Because certain types of data structures are so commonly used in programming, MFC defines collection classes that enable you to get these common data structures initialized quickly and manipulated easily. MFC includes collection classes for arrays, linked lists, and mapping tables. Each of these types of collections contain elements that represent the individual pieces of data that comprise the collection. In order to make it easier to access these elements, MFC defines a set of functions, shown in Table 23.3, that you can override for a particular data type.
Table 23.3 Collection Class Helper Functions
Function | Description |
CompareElements() | Checks elements for equality |
ConstructElements() | Constructs a new element (works similarly to a class constructor) |
DestructElements() | Destroys elements (works similar to a class destructor) |
DumpElements() | Provides diagnostic output in text form. |
HashKey() | Calculates hashing keys |
SerializeElements() | Saves or loads elements to or from an archive |
If you've done much Visual C++ programming, you know that MFC features a special string class, called CString, that makes string handling under C++ less cumbersome. CString objects are used extensively throughout MFC programs. Even when dealing with strings in a resource's string table, CString objects can come in handy, as the following global functions, which replace format characters in string tables, show (see Table 23.4). There's also a global function for displaying a message box.
Table 23.4 CString Formatting and Message Box Functions
Function | Description |
AfxFormatString1() | Replaces the format characters (i.e. %1) in a string resource with a given string |
AfxFormatString2() | Replaces the format characters "%1" and "%2" in a string resource with the given strings |
AfxMessageBox() | Displays a message box |
The most commonly used constants are those that define a portable set of data types. You've seen tons of these constants, which are named with all uppercase letters, used in Windows programs. You'll recognize many of these from the Windows SDK. Others are included only as part of Visual C++. You use these constants exactly as you would any other data type. For example, to declare a Boolean variable, you'd write something like this:
BOOL flag;
Table 23.5 lists the most commonly used data types defined by Visual C++ for Windows 95 and NT.
Table 23.5 Commonly Used Data Types
Constant | Data Type |
BOOL | Boolean value |
BSTR | 32-bit pointer to character data used with OLE |
BYTE | 8-bit unsigned integer |
COLORREF | 32-bit color value |
DWORD | 32-bit unsigned integer |
LONG | 32-bit signed integer |
LPARAM | 32-bit window-procedure parameter |
LPCRECT | 32-bit constant RECT structure pointer |
LPCSTR | 32-bit string-constant pointer |
LPSTR | 32-bit string pointer |
LPVOID | 32-bit void pointer |
LRESULT | 32-bit window-procedure return value |
POSITION | The position of an element in a collection |
UINT | 32-bit unsigned integer |
WNDPROC | 32-bit window-procedure pointer |
WORD | 16-bit unsigned integer |
WPARAM | 32-bit window-procedure parameter |
After you have your program written, you're far from done. Then comes the grueling task of testing, which means rolling up your sleeves, cranking up your debugger, and weeding out all the gotchas hiding in your code. Luckily, MFC provides many macros, functions, and global variables that you can use to incorporate diagnostic abilities into your projects. Using these tools, you can do everything from printing output to a debugging window to checking the integrity of memory blocks. Table 23.6 lists these valuable diagnostic macros, functions, and global variables.
Table 23.6 Diagnostic Macros, Functions, and Global Variable
Symbol | Description |
AfxCheckMemory() | Verifies the integrity of allocated memory. |
AfxDoForAllClasses() | Calls a given iteration function for all classes that are derived from CObject and that incorporate run-time type checking. |
AfxDoForAllObjects() | Calls a given iteration function for all objects that were derived from CObject and that were allocated with the new operator. |
afxDump | A global CDumpContext object that enables a program to send information to the debugger window. |
AfxDump() | Dumps an object's state during a debugging session. |
AfxEnableMemoryTracking() | Toggles memory tracking. |
AfxIsMemoryBlock() | Checks that memory allocation was successful. |
AfxIsValidAddress() | Checks that a memory address range is valid for the program. |
AfxIsValidString() | Checks string pointer validity. |
afxMemDF | A global variable that controls memory-allocation diagnostics. Can be set to allocMemDF, DelayFreeMemDF, or checkAlwaysMemDF. |
AfxSetAllocHook() | Sets a user-defined hook function that is called whenever memory allocation is performed. |
afxTraceEnabled | A global variable that enables or disables TRACE output. |
afxTraceFlags | A global variable that enables the MFC reporting features. |
ASSERT | Prints a message and exits the program if the assert expression is false. |
ASSERT_VALID | Validates an object by calling the object's AssertValid() function. |
DEBUG_NEW | Used in place of the new operator in order to trace memory-leak problems. |
TRACE | Creates formatted strings for debugging output. |
TRACE0 | Same as TRACE but requires no arguments in the format string. |
TRACE1 | Same as TRACE but requires one argument in the format string. |
TRACE2 | Same as TRACE but requires two arguments in the format string. |
TRACE3 | Same as TRACE but requires three arguments in the format string. |
VERIFY | Like ASSERT, but VERIFY evaluates the assert expression in both the Debug and Release versions of MFC. If the assertion fails, a message is printed, and the program is halted only in the Debug version. |
One of the newest elements of the C++ language is exceptions, which give a program greater control over how errors are handled. MFC increases the value of exceptions by defining a set of macros and functions that you can use to better handle errors in your applications. These macros and functions are listed in Table 23.7.
Table 23.7 Exception Macros and Functions
Symbol | Description |
AfxAbort() | Terminates an application upon a fatal error |
AfxThrowArchiveException() | Throws an archive exception |
AfxThrowDAOException() | Throws a CDaoException |
AfxThrowDBException() | Throws a CDBException |
AfxThrowFileException() | Throws a file exception |
AfxThrowMemoryException() | Throws a memory exception |
AfxThrowNotSupportedException() | Throws a not-supported exception |
AfxThrowOleDispatchException() | Throws an OLE automation exception |
AfxThrowOleException() | Throws an OLE exception |
AfxThrowResourceException() | Throws a resource-not-found exception |
AfxThrowUserException() | Throws an end user exception |
AND_CATCH | Begins code that will catch specified exceptions not caught in the preceding TRY block |
AND_CATCH_ALL | Begins code that will catch all exceptions not caught in the preceding TRY block |
CATCH | Begins code for catching an exception |
CATCH_ALL | Begins code for catching all exceptions |
END_CATCH | Ends CATCH or AND_CATCH code blocks |
END_CATCH_ALL | Ends CATCH_ALL code blocks |
THROW | Throws a given exception |
THROW_LAST | Throws the most recent exception to the next handler |
TRY | Starts code that'll accommodate exception handling |
The exception macros listed in Table 23.7 are included in MFC only to provide compatibility with earlier versions of the language. New programs should not use the macros, but rather the new exception-specific keywords such as try and catch.
See Understanding Exceptions, (ch. 21)
Windows is an event-driven operating system, which means that every Windows application must handle a flood of messages that flow between an application and the system. MFC does away with the clunky switch statements that early Windows programmers had to construct in order to handle messages and replaces those statements with a message map, which is nothing more than a table that matches a message with its message handler. In order to simplify the declaration and definition of these tables, MFC defines a set of message map macros. Many of these macros, which are listed in Table 23.8, will already be familiar to experienced MFC programmers.
Table 23.8 Message Map Macros
Macro | Description |
BEGIN_MESSAGE_MAP | Begins a message map definition |
DECLARE_MESSAGE_MAP | Starts a message map declaration |
END_MESSAGE_MAP | Ends a message map definition |
ON_COMMAND | Begins a command-message message map entry |
ON_COMMAND_RANGE | Begins a command-message message map entry that maps multiple messages to a single handler |
ON_CONTROL | Begins a control notification message map entry |
ON_CONTROL_RANGE | Begins a control notification message map entry that maps multiple control IDs to a single handler |
ON_MESSAGE | Begins a user-message message map entry |
ON_REGISTERED_MESSAGE | Begins a registered user-message message map entry |
ON_UPDATE_COMMAND_UI | Begins a command-update message map entry |
ON_UPDATE_COMMAND_UI_RANGE | Begins a command-update message map entry that maps multiple command-update messages to a single handler |
Frequently in your programs, you need access to information about classes at runtime. MFC supplies a macro for obtaining this type of information in a CRuntimeClass structure. In addition, the MFC application frameworks relies on a set of macros to declare and define runtime abilities (such as object serialization and dynamic object creation). If you've used AppWizard at all, you've seen these macros used in the generated source code files. If you're an advanced MFC programmer, you might have even used these macros yourself. Table 23.9 lists the run-time macros and their descriptions.
Table 23.9 Runtime Services Macros
Macro | Description |
DECLARE_DYNAMIC | Used in a class declaration to enable runtime class information access. |
DECLARE_DYNCREATE | Used in a class declaration to allow the class (derived from CObject) to be created dynamically. Also, allows runtime class information access. |
DECLARE_OLECREATE | Used in a class declaration to allow object creation with OLE automation. |
DECLARE_SERIAL | Used in a class declaration to allow object serialization, as well as runtime class information access. |
IMPLEMENT_DYNAMIC | Used in a class implementation to enable runtime class information access. |
IMPLEMENT_DYNCREATE | Used in a class implementation to allow dynamic creation of the object and runtime information access. |
IMPLEMENT_OLECREATE | Used in a class implementation to enable object creation with OLE. |
IMPLEMENT_SERIAL | Used in a class implementation to allow object serialization and runtime class information access. |
RUNTIME_CLASS | Returns a CRuntimeClass structure for the given class. |
As you can see, the macros in Table 23.9 deal with run-time information. In addition to the macros, Run-Time Type Information (RTTI) was added to C++ so that programmers could obtain information about objects at runtime. This capability is especially useful when you're dealing with polymorphic objects, because it enables your program to determine at runtime what exact type of object it's currently working with.
See Using Run-Time Type Information, (ch. 21)
There are myriad standard messages that can be generated by a user of a Windows application. For example, whenever the user selects a menu command from a standard menu like File or Edit, the program sends a message. Each of these standard commands is represented by an ID. In order to relieve the programmer of having to define the dozens of IDs that are often used in a Windows application, MFC defines these symbols in a file called AFXRES.H. Some of these IDs have obvious purposes (for example, ID_FILE_OPEN), but many others are used internally by MFC for everything from mapping standard Windows messages to their handlers to defining string table IDs to assigning IDs to toolbar and status bar styles. There are far too many of these identifiers to list here. However, if you're interested in seeing them, just load the AFXRES.H file from your Visual C++ installation folder.