C++ equivalent for VB TypeOf operator?

[Bob Altman]

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

 

[Cholo Lennon]

Hi all,

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

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

The operator returns 0 (or nullptr in C++ CLI) if the convertion fails.

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

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

The general pattern to use dynamic_cast is:

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



Regards

 

[Jialiang Ge [MSFT]]

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 ([email protected], remove 'online.')
Microsoft Online Community Support

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[Bob Altman]

Thanks a million!

 

[Cholo Lennon]

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.

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