[Mingw-users] Re: c++ exception question

[Phillip S. <ps...@cf...>]

I'm a little confused here.  C++ exceptions are caught with a try/catch 
block, win32 SEH exceptions are caught with a __try/__except block.  gcc 
does not support SEH exceptions.  I'm not sure why your code there has a 
try { __try1 in it.  try is a C++ try, what is __try1 and __except1?  If 
you want to catch an access violation, you need to use a SEH exception 
handler; C++ catch statements will not catch seg faults ( unless the 
compiler is very broken and non compliant, like VC 5 was ).

At 09:57 PM 1/3/2002 -0800, you wrote:
>I'm attaching a GCC-compiled C++ DLL to a Windows application (XEmacs
>21.4.6). In my DLL, I need to catch segfaults, so I've set up this
>structured exception handler:
>
>inline
>EXCEPTION_DISPOSITION
>_catch1(_EXCEPTION_RECORD *exception_record,
>         void *err,
>         _CONTEXT *context,
>         void *par)
>{
>     throw exception_record;
>}
>
>#define CHECK_FOR_HARMONIA_ERROR_BEGIN()  \
>    try { \
>      __try1(_catch1)
>
>#define CHECK_FOR_HARMONIA_ERROR_END() \
>     __except1  \
>     } catch(_EXCEPTION_RECORD *seh) {  \
>       if (error_handler != NULL) \
>         error_handler(seh_to_pooled_string(seh)); \
>     } catch(PooledString pserror) { \
>       if (error_handler != NULL) \
>         error_handler(pserror); \
>     }
>
>I wrap calls with CHECK_FOR_HARMONIA_ERROR_BEGIN() and END, and should
>call an error handler I defined that prints out a message to XEmacs'
>console.
>
>If I compile XEmacs (a C application) with GCC (mingw), instead of
>catching any errors, my application disappears whenever a segfault
>occurs. I used VisStudio to debug XEmacs and catch the exception, and it
>said that there was a segfault while running _local_unwind2. From what I
>know of that function, that's what happens when MS is trying to run your
>exception handler. From the PC, it appears it's my exception that's
>running, and since there's only one line, it's the C++ throw call that's
>failing to execute.
>
>However, and here's the funny thing, if I compile XEmacs with MSVC,
>first of all, my segfault (which above occurred in my DLL and is handled
>there, not in XEmacs) doesn't occur, and I can't catch exceptions at
>all. When a real segfault does occur (M-x make-harmonia-segfault <grin>)
>I get an abnormal termination error dialog box from MS Windows 2000,
>which means my exception handler didn't run at all.
>
>What's going on here? On one hand, i have a spurious seg fault that
>causes my exception handler to itself segfault, and then just by
>changing the host executable for my DLL, the segfault goes away, but any
>ability to catch C exceptions does too.
>
>Does anyone have any insight into this? Are there any libraries that gcc
>links into a binary executable that can affect the DLLs that are loaded?
>How do C++ DLLs deal with being loaded into C executables? Do they come
>with their own exception library that g++ links in?
>
>Thanks
>
>andrew