cpp: catch exception with ellipsis and see the information

Question

I know that you can catch "all exceptions" and print the exception by

try
{
    //some code...
}catch(const std::exception& e) {
   cout << e.what();
}

but this is just for exceptions derived from std::exception. I was wondering if there is a way to get some information from an ellipsis catch

try
{
    //some code...
}catch(...) {
   // ??
}

If the mechanism is the same as ellipsis for functions then I should be able to do something like casting the argument of the va_list and trying to call the what() method.

I haven't tried it yet but if someone knows the way I'd be excited to know how.

Lyrism

Have you ever wondered how it could work to call what() on an int when s.o. throws one ? – Brundisium

Obviously what I suggested wouldn't always work. I'm looking for a way to get something from it. – Lyrism

Answer 1

Sorry, you can't do that. You can only access the exception object in a catch block for a specific exception type.

Jassy

Answer 2

From C++11 and onwards, you can use std::current_exception &c:

std::exception_ptr p;
try {
    
} catch(...) {
    p = std::current_exception();
}

You can then "inspect" p by taking casts &c, albeit not in a portable way.

In earlier standards there is no portable way of intersecting the exception at a catch(...) site, other than re-throwing it with throw;.

Baltoslavic

what is the &c you wrote? – Lyrism

That's new to me (the &c) :) Can you show in your answer what can you do with this exception_ptr (what is the advantage)? – Lyrism

You can't get any details out of std::exception_ptr, you can only rethrow it. – Martensite

"&c" means "et cetera" ("and so on"). The Latin word "et" means "and". Replacing it with an ampersand saves a character and adds a somewhat old-fashioned flavor, but given that it confuses people here (where many people are not native English speakers), perhaps "and so on" would be better. – Majewski