Exception Handling Topics (MFC)

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This article explains the exception-handling mechanisms available in MFC. Two mechanisms are available:

  • C++ exceptions, available in MFC version 3.0 and later

  • The MFC exception macros, available in MFC versions 1.0 and later

If you’re writing a new application using MFC, you should use the C++ mechanism. You can use the macro-based mechanism if your existing application already uses that mechanism extensively.

You can readily convert existing code to use C++ exceptions instead of the MFC exception macros. Advantages of converting your code and guidelines for doing so are described in the article Exceptions: Converting from MFC Exception Macros.

If you have already developed an application using the MFC exception macros, you can continue using these macros in your existing code, while using C++ exceptions in your new code. The article Exceptions: Changes to Exception Macros in Version 3.0 gives guidelines for doing so.

Note   To enable C++ exception handling in your code, select Enable Exception Handling in the C++ Language category of the C/C++ tab of the Project Settings dialog box, or use the /GX compiler option. The default is /GX–, which disables exception handling.

This article covers the following topics:

  • When to use exceptions

  • MFC exception support

  • Further reading about exceptions

When to Use Exceptions

Three categories of outcomes can occur when a function is called during program execution: normal execution, erroneous execution, or abnormal execution. Each category is described below.

  • Normal execution

    The function may execute normally and return. Some functions return a result code to the caller, which indicates the outcome of the function. The possible result codes are strictly defined for the function and represent the range of possible outcomes of the function. The result code can indicate success or failure or can even indicate a particular type of failure that is within the normal range of expectations. For example, a file-status function can return a code that indicates that the file does not exist. Note that the term “error code” is not used because a result code represents one of many expected outcomes.

  • Erroneous execution

    The caller makes some mistake in passing arguments to the function or calls the function in an inappropriate context. This situation causes an error, and it should be detected by an assertion during program development. (For more information on assertions, see the article Diagnostics: The ASSERT Macro.)

  • Abnormal execution

    Abnormal execution includes situations where conditions outside the program’s control, such as low memory or I/O errors, are influencing the outcome of the function. Abnormal situations should be handled by catching and throwing exceptions.

Using exceptions is especially appropriate for abnormal execution.

MFC Exception Support

Whether you use the C++ exceptions directly or use the MFC exception macros, you will use or CException-derived objects that may be thrown by the framework or by your application.

MFC provides several predefined kinds of exceptions:

Exception class Meaning
Out-of-memory
File exception
Archive/Serialization exception
Response to request for unsupported service
Windows resource allocation exception
Database exceptions (DAO classes)
Database exceptions (ODBC classes)
OLE exceptions
Dispatch (automation) exceptions
Exception that alerts the user with a message box, then throws a generic

Note   MFC supports both C++ exceptions and the MFC exception macros. MFC does not directly support Windows NT structured exception handlers (SEH), as discussed in Exception Handling Topics (SEH).

Further Reading About Exceptions

The following articles explain using the class library for exception handing:

The following articles compare the MFC exception macros with the C++ exception keywords and explain how you can adapt your code: