Howto rethrow an exception outside a catch block?

[reuce-google]

Hi folks,

I want to store an exception and rethrow it later:

CException m_pEc = NULL; // Class variable.

try
{
throw new CMemoryExceptio n();
}
catch (CException * pEc) // Catch all exceptions derived from
CException.
{
m_pEc = pEc; // Store Exception.
}

.....

CMemoryExceptio n is derived from CException. But if I now throw m_pEc
the Exception raised will be caught merely by CException catch blocks,
unfortunately:

try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

.....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

[reuce-google]

Hello Alf,

In the catch block you can do

throw;

if you had read my subject carefully... ;-)

Note that it's not a good idea to throw pointers to dynamically
allocated memory, for it may be caught by a catch(...), and who's then
to deallocate?

Better use standard C++ exceptions.

Thanks for that advice. It's me who deallocates, so I can deal with
that.

Ron.

[reuce-google]

Better use standard C++ exceptions.

>
Thanks for that advice. It's me who deallocates, so I can deal with
that.

Sorry, I didn't read your answer carefully. But it is still not the
point.

Ron.

[Pete Becker]

On 2007-08-08 09:46:53 -0400, re**********@ya hoo.de said:

>
How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

You can't. The next version of the C++ standard will provide a
mechanism for doing this:

std::exception_ ptr ptr = 0;
catch(whatever)
{
ptr = std::current__e xception();
}
std::rethrow_ex ception(ptr);

There are no compilers that support this today.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)

[Bernd Strieder]

Hello,

re**********@ya hoo.de wrote:

>
try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

Add a virtual rethrow method to the base class, which is overwritten in
all derived classes to throw itself, i.e. with the right type. Then
call that method.

Bernd Strieder

[Bernd Strieder]

Hello,

re**********@ya hoo.de wrote:

>
try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

Add a virtual rethrow method to the base class, which is overwritten in
all derived classes to throw itself, i.e. with the right type. Then
call that method.

Bernd Strieder

[Bernd Strieder]

Hello,

re**********@ya hoo.de wrote:

>
try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

Add a virtual rethrow method to the base class, which is overwritten in
all derived classes to throw itself, i.e. with the right type. Then
call that method.

Bernd Strieder

[Bernd Strieder]

Hello,

re**********@ya hoo.de wrote:

>
try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

Add a virtual rethrow method to the base class, which is overwritten in
all derived classes to throw itself, i.e. with the right type. Then
call that method.

Bernd Strieder

[Bernd Strieder]

Hello,

re**********@ya hoo.de wrote:

>
try
{
CException * pEc = m_pEc;
m_pEc = NULL; // Clear variable.
throw pEc;
}
catch (CMemoryExcepti on * pEc)
{
// Won't catch the exception.
}
catch (CException * pEc)
{
// Will catch the exception.
}

....

How can I rethrow the exception, so that it will be thrown with the
right type information (CMemoryExcepti on) - even if I don't know the
type beforehand?

Add a virtual rethrow method to the base class, which is overwritten in
all derived classes to throw itself, i.e. with the right type. Then
call that method.

Bernd Strieder