C++ std::exception between Libraries

Question

When I throw an exception in a library, that exception does not get caught by the caller.

To illustrate, if I have this function in a static library:

#include <exception>

void TestClass::ThrowException()
{
   throw new std::exception();
}

... and then call it from an executable:

TestClass t;
try
{
   t.ThrowException();
}
catch (std::exception e)
{
}
catch (...)
{
}

... it is the second catch that receives the exception, not the first, which I did not expect. I suspect that there is some marshalling between the libraries that I am not aware of, which is causing the exception type to not be recognised.

Is it possible to pass an exception between two binaries so that it is recognised as a 'std::exception' by the caller? As a secondary question, is this a good idea?

I am targeting Windows, working with Visual Studio.

I've come from a managed (C#) background, so I would love to get a deeper understanding of what's going on here, and what is 'best practice# in C++. — Chris Spicer, Sep 11 '14 at 15:43
try `catch(std::exception& e)` instead of `catch(std::exception e)` — Arkady, Sep 11 '14 at 15:46
Looking at this a second time, you `throw new` which is going to be a pointer. See [How to throw a C++ exception](http://stackoverflow.com/questions/8480640/how-to-throw-a-c-exception). In other words, a lot of the places you use `new` in C#, you would not do the same in C++. — crashmstr, Sep 11 '14 at 15:46
crashmstr is right! And throwing exceptions between libraries is very bad architecture idea. — Arkady, Sep 11 '14 at 15:47
@Arkady: Is it? As long as they share the runtime-library, everything is fine. — Deduplicator, Sep 11 '14 at 15:53
@crashmstr: The comments correct the accepted answer considerably in important points... — Deduplicator, Sep 11 '14 at 15:59
@crashmstr - I appreciate that advice. Thank you all for your contribution. — Chris Spicer, Sep 11 '14 at 16:09

score 4 · Accepted Answer · answered Sep 11 '14 at 15:49

throw new std::exception();

You are throwing an exception you have created on the heap, so you need to catch it as a pointer:

catch (std::exception *e)

However don't ever do that (you won't know where to delete your allocated memory). Instead just throw an object on the stack:

throw std::exception();

Last point. Don't catch by value, catch by reference. This is because when you subclass your exceptions later you won't slice them. And if you want to be completely correct catch by const reference:

catch (const std::exception& e)

If you're new to all this recommended reading is Effective C++ and it's sequel by Scott Meyers.

Thank you for a clear answer and also recommended reading. Turns out that my understanding of how to throw exceptions in C++ was way off base. — Chris Spicer, Sep 11 '14 at 16:08

C++ std::exception between Libraries

1 Answers1