Structured exception vs C++ exception

[Lane Yu]

How to rasie a exception that can only be caught by __try/__except, but cannot be caught by try/catch? In a Windows application written by VC. What time to use structured exception instead of C++ exception?

[Stephen Hewitt]

In standard C++ try/catch can only catch C++ exceptions: that is only exceptions that are raised by the C++ throw statement. Unfortunately some version of Microsoft Visual C++ (6.0 and below) do not follow the standard in this regard. This was fixed in later versions but the old non-standard behaviour can be selected with the /EHa[^] switch (not a good idea in general). __try/__except is a low level construct and can catch any exception. Note however that with __try/__except the destructors of objects on the stack as it is unwound are not called, so this construct doesn’t play nice with C++. It will break the RAII pattern for example. To explicitly raise a C++ exception use the C++ throw keyword. To explicitly raise an exception (not a C++ exception) you have two options:    1. Do something wrong! For example to raise a divide by zero exception try to divide by zero; to raise an access violation attempt to access an invalid memory location.    2. Use the Win32 RaiseException[^] function.

Steve

[Mark Salsbery]

Stephen Hewitt wrote:

so this construct doesn’t play nice with C++.

Excellent reply. Where were you when I learned that the hard way? :)

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

[Lane Yu]

But in my testing program, all kinds of exceptions including zero-dividing or NULL pointer can be caught by catch(...). Why? Does that mean we can always use C++ try/catch in C++ programs?

[Stephen Hewitt]

Lane Yu wrote:

But in my testing program, all kinds of exceptions including zero-dividing or NULL pointer can be caught by catch(...). Why? Does that mean we can always use C++ try/catch in C++ programs?

As my previous post indicated, the fact that you can use try/catch to catch NULL pointer references and zero-dividing indicates that:  - You're using an old and non-standard compiler such as Microsoft Visual Studio 6.  - You're using a compiler with a non-standard extension with enables this non-standard behaviour; such as the later Microsoft compiler's /EHa switch. In standard C++ try/catch can NOT catch these exceptions!

Steve

[Lane Yu]

Thank you. I'm using VC6.