Determining exception type after the exception is

Question

Is there a way to determine the exception type even know you caught the exception with a catch all?

Example:

try
{
   SomeBigFunction();
}
catch(...)
{
   //Determine exception type here
}

Answer 1

provided that c++11 available,

bool throwing_func()
{
    // something is wrong...
    throw char('5');

    // ...

    return true;
}

void exception_handler(std::exception_ptr _Eptr)
{
    try 
    {
        if (_Eptr) {std::rethrow_exception(_Eptr);}
    }


    catch(int _Xi)
    {
        std::cout << "int\n";
    }

    catch(char _Xc)
    {
        std::cout << "char\n";
    }

    catch(const std::exception& _Xe)
    {
       std::cout << "std::exception " << _Xe.what() << "\n";
    }

    catch (...)
    {// develop more catch cases above to avoid what follows
        std::cout << "unhandled exception\n";
        // grande problema
    }
}

int main()
{

    try
    {
        throwing_func();
    }

    catch(...)
    {
        //Determine exception type here

         exception_handler(std::current_exception());
    }

    return 0;
}

Answer 2

If you need to handle exceptions differently based on what they are, you should be catching specific exceptions. If there are groups of exceptions that all need to be handled identically, deriving them from a common base class and catching the base class would be the way to go. Leverage the power and paradigms of the language, don't fight against them!

Answer 3

No.

Doing so would at the very least require you to be able to access the current exception. I do not believe there is a standard way of doing this.

Once you had the exception instance, you would have to use a type inspection algorithm. C++ doesn't have inherent support for this. At best you would have to have a big if/elseif statement with dynamic_cast's to check the type.

Answer 4

This question was asked some time ago and I'm offering this answer as a companion to the accepted answer from 9 years ago. I'd have to concur with that respondent that that answer, "... is not very useful." Further, it opens the door to an exception which was once handled being unhandled. To illustrate, let me build upon the respondent's answer

#include <iostream>
#include <exception>

class E1 : public std::exception {};
class E2 : public std::exception {};
class E3 : public std::exception {};

int main() {
    try {
        throw E3();
    }
    catch( ... ) {
        try {
            // OOOPS!!! E3 is now unhandled!!!!!!
            throw;
        }
        catch( const E1 & e ) {
            std::cout << "E1\n";
        }
        catch( const E2 & e ) {
            std::cout << "E2\n";
        }
    }
}

An alternative to this approach would be the following:

#include <iostream>
#include <exception>

class E1 : public std::exception {};
class E2 : public std::exception {};
class E3 : public std::exception {};

int main() {
    try {
        throw E3();
    }
    catch( const E1 & e ) {
        std::cout << "E1\n";
    }
    catch( const E2 & e ) {
        std::cout << "E2\n";
    }
    catch( ... ) {
        std::cout << "Catch-all...";
    }
}

This second approach seems to be tantamount to the first and has the advantage of specifically handling E1 and E2 and then catching everything else. This is offered only as an alternative.

Please note that, according to C++ draft of 2011-02-28, paragraph 15.3, bullet item 5, "If present, a ... handler shall be the last handler for its try block."

Answer 5

There is no standard, portable way to do this. Here's a non-portable way to do it on GCC and clang

#include <iostream>
#include <cxxabi.h>

const char* currentExceptionTypeName()
{
    int status;
    return abi::__cxa_demangle(abi::__cxa_current_exception_type()->name(), 0, 0, &status);
}

int main()
{
    try {
        throw std::string();
    } catch (...) {
        std::cout<<"Type of caught exception is "<<currentExceptionTypeName()<<std::endl;
    }

    return 0;
}

Output:

Type of caught exception is std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >

Answer 6

You can actully determine type inside a catch(...), but it is not very useful:

#include <iostream>
#include <exception>

    class E1 : public std::exception {};
    class E2 : public std::exception {};

    int main() {
        try {
            throw E2();
        }
        catch( ... ) {
            try {
                throw;
            }
            catch( const E1 & e ) {
                std::cout << "E1\n";
            }
            catch( const E2 & e ) {
                std::cout << "E2\n";
            }
        }
    }