C++ equivalent for VB TypeOf operator?

Hi all,

What's the C++ equivalent for the VB TypeOf operator. For example:

void ReportError(System::Exception^ ex)
{
// Psuedo-VB syntax
if (TypeOf ex Is System::OperationCanceledException) return;

// Decode the exception and tell the user about it...
<...>
}

TIA - Bob

re: C++ equivalent for VB TypeOf operator?

Bob Altman wrote:dynamic_cast (http://msdn.microsoft.com/en-us/library/cby9kycs.aspx)

The operator returns 0 (or nullptr in C++ CLI) if the convertion fails.
The general pattern to use dynamic_cast is:

if (System::OperationCanceledException^ opCanEx = dynamic_cast<System::OperationCanceledException^>( ex)) {
// Use opCanEx
...
}



Regards

--
Cholo Lennon
Bs.As.
ARG

re: C++ equivalent for VB TypeOf operator?

Good morning Bob and Cholo

If you would like to handle System::OperationCanceledException and all the
subclasses of System::OperationCanceledException in the if statement, we
can use Cholo's suggestion of dynamic_cast:

if (dynamic_cast<System::OperationCanceledException^> (ex))
{
// if ex belongs to a subclass of System::OperationCanceledException, the
above if statement will still return true.
// Decode the exception and tell the user about it
}

If you would like to only handle System::OperationCanceledException and
disregard the subclasses of OperationCanceledException, the 'typeid'
keyword will be proper:
http://msdn.microsoft.com/en-us/library/kwd9abya.aspx

void ReportError(System::Exception^ ex)
{
if (ex->GetType() == System::OperationCanceledException::typeid)
{
// Decode the exception and tell the user about it
}
}

Please let me know whether the above information is helpful to you or not.
If you have any other questions/concerns, feel free to tell me.

Have a very nice day!

Regards,
Jialiang Ge (jialge@online.microsoft.com, remove 'online.')
Microsoft Online Community Support

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re: C++ equivalent for VB TypeOf operator?

Thanks a million!

re: C++ equivalent for VB TypeOf operator?

"Cholo Lennon" <chololennon@hotmail.comkirjutas:
dynamic_cast only works on polymorphic pointers/references (i.e. having
at least one virtual function). While it's true that std::exception is
polymorphic, there might be other exception objects which are not. In C++
it is possible to distinguish them, but only if you know the types in
advance.

In such a situation, it is often the case that one does not have an idea
which exceptions might arise, so I give an example with a catch(...)
clause. This by itself does not give any information about the exception
type so it has to be "resurrected" by another function:

std::string ResurrectException();

int f() {
try {
// actual code ...
} catch(...) {
std::string msg = ResurrectException();
std::cerr << "Exception: " << msg << "\n";
}
}


std::string ResurrectException() {
try {
throw; // valid only when called from inside a catch block
} catch(const std::exception& e) {
return e.what();
} catch(int e) {
std::ostringstream os;
os << e;
return "Int exception: " + os.str();
} catch(const my_private_exception& e) {
return e.ToString();
} catch(...) {
return "Unknown exception";
}
}

re: C++ equivalent for VB TypeOf operator?

Paavo Helde wrote:You're right, but just a clarification: the OP asked about "TypeOf" with a .Net exception (not std::exception). BTW all .Net
exceptions are polymorphics.

Regards

--
Cholo Lennon
Bs.As.
ARG

re: C++ equivalent for VB TypeOf operator?

"Cholo Lennon" <chololennon@hotmail.comkirjutas:Yes sorry, I have to check more carefully in which ng I am posting!

Cheers
Paavo