exceptions-using-mfc-macros-and-cpp-exceptions.md

description	title	ms.date	helpviewer_keywords	ms.assetid
Learn more about: Exceptions: Using MFC Macros and C++ Exceptions	Exceptions: Using MFC Macros and C++ Exceptions	11/04/2016	exception objects [MFC] memory leaks [MFC], exception object not deleted exception handling [MFC], MFC try-catch exception handling [MFC], mixing MFC macros and C++ keywords exception objects [MFC], deleting exceptions [MFC], MFC macros vs. C++ keywords catch blocks [MFC], mixed exception handling [MFC], mixed-language nested try blocks [MFC] catch blocks [MFC], explicitly deleting code in try-catch exception handling [MFC], nested try blocks heap corruption [MFC] nested catch blocks [MFC]	d664a83d-879b-44d4-bdf0-029f0aca69e9

Exceptions: Using MFC Macros and C++ Exceptions

This article discusses considerations for writing code that uses both the MFC exception-handling macros and the C++ exception-handling keywords.

This article covers the following topics:

• Mixing exception keywords and macros

• Try blocks inside catch blocks

Mixing Exception Keywords and Macros

You can mix MFC exception macros and C++ exception keywords in the same program. But you cannot mix MFC macros with C++ exception keywords in the same block because the macros delete exception objects automatically when they go out of scope, whereas code using the exception-handling keywords does not. For more information, see the article Exceptions: Catching and Deleting Exceptions.

The main difference between the macros and the keywords is that the macros "automatically" delete a caught exception when the exception goes out of scope. Code using the keywords does not; exceptions caught in a catch block must be explicitly deleted. Mixing macros and C++ exception keywords can cause memory leaks when an exception object is not deleted, or heap corruption when an exception is deleted twice.

The following code, for example, invalidates the exception pointer:

[!code-cppNVC_MFCExceptions#10]

The problem occurs because e is deleted when execution passes out of the "inner" CATCH block. Using the THROW_LAST macro instead of the THROW statement will cause the "outer" CATCH block to receive a valid pointer:

[!code-cppNVC_MFCExceptions#11]

Try Blocks Inside Catch Blocks

You cannot re-throw the current exception from within a try block that is inside a CATCH block. The following example is invalid:

[!code-cppNVC_MFCExceptions#12]

For more information, see Exceptions: Examining Exception Contents.

See also

Exception Handling