compile error about destructor

Hello everyone,


When change from __try to try, and __except(GetExceptionCode()) to catch(...), compile can pass.

Compile error and code are,

1>Compiling...
1>main.cpp
1>d:\visual studio 2008\projects\test_exception1\test_exception1\main .cpp(30) : warning C4509: nonstandard extension used: 'main' uses SEH and 'foo1' has destructor
1> d:\visual studio 2008\projects\test_exception1\test_exception1\main .cpp(28) : see declaration of 'foo1'
1>d:\visual studio 2008\projects\test_exception1\test_exception1\main .cpp(35) : error C2712: Cannot use __try in functions that require object unwinding

Code:

---

#include <iostream>
#include <excpt.h>
#include <windows.h>

using namespace std;

class Foo
{
public:
        Foo()
        {
                cout << "constructing Foo" << endl;
        }

        virtual ~Foo()
        {
                cout << "destrucing Foo" << endl;
        }

};

int main()
{
        int* address = NULL;

        __try{

                Foo foo1;
                (*address) = 1024;
        } __except (GetExceptionCode())
        {
                cout << "access violation caught" << endl;
        }
        return 0;
}

---

regards,
George

So you can't use structured exception handling with objects that have a destructor.

--
Mats

Hi Mats,


But why using try/catch is ok? It is still structured exception catched.

Try to replace the __try to try and replace __except to catch(...).

Quote:

---

Originally Posted by matsp

So you can't use structured exception handling with objects that have a destructor.

--
Mats

---

regards,
George

try/catch are able to CATCH a SE, but that doesn't mean that they are the same thing, right?

--
Mats

Thanks Mats,


What is the difference betwen try/catch and __try/__except when dealing with structured exception?

Why __try/__except is more strict?

Quote:

---

Originally Posted by matsp

try/catch are able to CATCH a SE, but that doesn't mean that they are the same thing, right?

--
Mats

---

regards,
George

perhaps this:

Quote:

---

Originally Posted by MSDN

Structured exception handling works with Win32 for both C and C++ source files. However, it is not specifically designed for C++. You can ensure that your code is more portable by using C++ exception handling. Also, C++ exception handling is more flexible, in that it can handle exceptions of any type. For C++ programs, it is recommended that you use the C++ exception-handling mechanism (try, catch, and throw statements).

---

From:
http://msdn2.microsoft.com/en-us/lib...19(VS.80).aspx

--
Mats

Hi Mats,


It is just a walkaround to replace structured exception with C++ exception, or even using set_se_translator to convert structured exception to C++ exception.

But it does not explain the reason why using try/catch is ok, but using __try/__except is not ok and their difference.

Quote:

---

Originally Posted by matsp

perhaps this:


From:
http://msdn2.microsoft.com/en-us/lib...19(VS.80).aspx

--
Mats

---

regards,
George

It does: SE exceptions are (as MSDN says) not designed for C++, so it doesn't "understand" how to destroy C++ objects - only how to catch exceptions in itself.

--
Mats

Thanks Mats,


But when we replace __try with try and replace __except with catch, we still catch structured exception, and destructor is called.

Output is,

constructing Foo
destructing Foo
access violation caught

You can see if we change the keyword, structured exception is caught and destructor is called before handler.

Quote:

---

Originally Posted by matsp

It does: SE exceptions are (as MSDN says) not designed for C++, so it doesn't "understand" how to destroy C++ objects - only how to catch exceptions in itself.

--
Mats

---

regards,
George

Yes, isn't this the same discussion about "are structured exceptions caught by catch" that we had a few days ago?

Yes, structured exceptions are caught by try/catch along with C++ throws [1], whilst __try/__except only catches structured exceptions.


[1] Unless you specifically ask the compiler to NOT catch structured exceptions with C++ catch-blocks - don't know what the exact way to tell the compiler this, but recent versions of MS VC++ is able to "not catch structured exceptions with C++ catch".

--
Mats

Hi Mats,


If you remove the destructor in the class, everything is fine with __try/__except. So, I think it is dealing with destructor. It is not the same as the question I asked before.

Any ideas?

Quote:

---

Originally Posted by matsp

Yes, isn't this the same discussion about "are structured exceptions caught by catch" that we had a few days ago?

Yes, structured exceptions are caught by try/catch along with C++ throws [1], whilst __try/__except only catches structured exceptions.


[1] Unless you specifically ask the compiler to NOT catch structured exceptions with C++ catch-blocks - don't know what the exact way to tell the compiler this, but recent versions of MS VC++ is able to "not catch structured exceptions with C++ catch".

--
Mats

---

regards,
George

It may not be THE SAME question, but it's related in the sense that you are asking about try/catch use for structured exceptions.

Of course it works when you don't have a destructor, since it's not requiring any C++ specific features to resolve the exception any longer - there is no destructor to call, so there's no reason to know how to unwind the stack, and thus the structured exception can just exit the block with no ill effects.

I guess if we summarize: If you WANT to catch structured exceptions ONLY, you can not use C++ language features within the __try/__except block. If you want to use C++ exceptions, then you can use try/catch, and if you ALSO want to catch structured exceptions, that will work as long as you have that feature enabled in the build.

--
Mats

Thanks Mats,


From your summarize, I think the logics is __try/__catch has no use and we should always use try/catch. :-)

Is that your point?

Quote:

---

Originally Posted by matsp

It may not be THE SAME question, but it's related in the sense that you are asking about try/catch use for structured exceptions.

Of course it works when you don't have a destructor, since it's not requiring any C++ specific features to resolve the exception any longer - there is no destructor to call, so there's no reason to know how to unwind the stack, and thus the structured exception can just exit the block with no ill effects.

I guess if we summarize: If you WANT to catch structured exceptions ONLY, you can not use C++ language features within the __try/__except block. If you want to use C++ exceptions, then you can use try/catch, and if you ALSO want to catch structured exceptions, that will work as long as you have that feature enabled in the build.

--
Mats

---

regards,
George

Quote:

---

Originally Posted by George2

Thanks Mats,


From your summarize, I think the logics is __try/__catch has no use and we should always use try/catch. :-)

Is that your point?

---

Nearly, but not exactly: __try/__except is useful in C - which doesn't support try/catch.

--
Mats

Thanks Mats,


I have understood your points.

There are some mysterious things that we could not explain now, but use try/catch is preferred. :-)

Quote:

---

Originally Posted by matsp

Nearly, but not exactly: __try/__except is useful in C - which doesn't support try/catch.

--
Mats

---

regards,
George