Javier Estrada wrote:
Well, it seems like it's bad both ways, isn't it.
On one hand, the assumption that only throw statements will result in
an exception is ridiculous.
I need to write C++ code to cope with SEH (e.g., accessing invalid
pointers, etc.). However, having objects with automatic storage
undestroyed poses yet another risk.
If you compile with /EHa there is no such risk.
Does translating the SEH exceptions to C++ exceptions help in any
way? I just read an article on The Code Project on replacing the
exceptions, but at the end it also recommends using a workaround or
the asynchronous model.
To translate exceptions to C++ exceptions you need to compile with /EHa.
Under VC7{.1}, you can go through the motions of converting SE's to C++
exceptions (__set_se_handler, etc), but in practice it won't work. Anywhere
the compiler optimized out the exception handling machinery, you translation
will just as effectively have been optimized out.
A couple things to be aware of when translating exceptions: First, you need
to call __set_se_handler separately in each thread. Second, there's only
one handler per thread, so if some other library has already done it, you'll
wipe out their handler. Finally, the translator is called each time a
catch() block is evaluated and an SE is being processed (it's called by the
exception filter routine, in Win32 SEH terms). If you have deeply nested
try/catch structures, you may translate a single excepiton many times before
it's handled (or not). Look for articles on Matt Peitrek and a series by
Bobby Schmidt on MSDN for lots of details into how exception handling works
if you need more info.
IMO, there's no downside to /EHa except for slightly slower code in some
cases. If you're serious about catching and dealing with structured
exceptions, or interacting with code that uses structured exceptions, you
must use /EHa. As Ronald pointed out, any interaction with the CLR requires
/EHa. In fact, in VC++ 2005 this is enforced by the compiler - adding /clr
implicitly add /EHa and will cause an error if you try to use /EHs.
-cd
