Ndtyjky

In g++ and clang++ (in Linux at least) the following typical message is shown after an exception is thrown and not catch (uncaught exception):

terminate called after throwing an instance of 'std::runtime_error'

  what():  Bye

For example in:

#include<stdexcept>

int main(){

  throw std::runtime_error("Bye");

}

How do I customize the error message while still having full access to the thrown exception?

The documentation (http://www.cplusplus.com/reference/exception/set_unexpected/) mentions set_unexpected (and set_terminate) but I don't know how the unexpected_handle has actual access to the exception being thrown, for example to call e.what() or something else.

Note: The reason behind this is that I want to customize the message for a more complicated exception class hierarchy that has more information than simple what(), and I want to display it if such type exception is thrown (but if a simple std::exception& is thrown the default is the same as the typical.

Note2: According to the two suggestions so far, "customize uncaught exceptions by catching the exceptions." Will look like what follows in the code. I was wondering if there is a way to do the same without adding a try-catch block to all main() code that I write.

#include<stdexcept>

int main() try{

   ....

}catch(std::exception& e){

  std::clog << "terminate called after throwing an instance of '" << typeid(e) << "'n"

            << "  what(): " << e.what() << 'n'

            << "otherinfo, like current timen";

}catch(alternative_exception& e){

  std::clog << "terminate called after throwing an instance of '" << typeid(e) << "'n"

            << "  what(): " << e.what() << 'n'

            << "  where(): " << e.where() << 'n'

            << "  how(): " << e.how() << 'n'

            << "othermember(): " << e.othermember() << 'n';

}

Apart from actually catching the exceptions you care about, std::set_terminate() and std::current_exception() (C++11) ought to be enough to do something interesting.

The hook for customizing the handling of uncaught exceptions is catching the exceptions.

Based on @JonPurdy (accepted) answer, I experimented with this code that seems to work, at least with gcc 4.7.2 and clang 3.2 in Linux. I have no idea how robust or portable it is (comments welcomed), I tried not to make assumptions about the default terminate handler:

#include<stdexcept>

#include<iostream>

#include<typeinfo> // for typeid



// a special exception, can be an abstract class, here it is concrete class to make the example shorter.

struct debug_exception : std::runtime_error{

    std::string where_;

    debug_exception(std::string what, std::string where) : std::runtime_error(what), where_(where){}

    virtual const char* where() const{return where_.c_str();}

};



std::terminate_handler my_default_terminate;



void my_verbose_terminate_handler(){

    try{

        throw;

    }catch(debug_exception& e){

        std::cerr << "my_verbose_terminate_handler called after throwing an instance of " 

                  << typeid(e).name() << std::endl; // or demangled

        std::cerr << "  what(): "  << e.what()  << std::endl;

        std::cerr << "  where(): " << e.where() << std::endl;

    }catch(...){

        my_default_terminate(); // probably __gnu_cxx::__verbose_terminate_handler();

    }

}

std::terminate_handler my_improve_terminate(){

    my_default_terminate = std::set_terminate(my_verbose_terminate_handler);

    return my_default_terminate;

}



int main(){

    my_improve_terminate();

//  throw 2; // says the default "terminate called after throwing an instance of 'int'"

//  throw std::runtime_error("bye"); // says the default "terminate called ... what(): bye"

    throw debug_exception("Bye", __PRETTY_FUNCTION__); // says my_verbose_terminate_handler called ... what(): Bye, where(): int main()"

}

Now I am experimenting with wrapping all the code in a class and call my_improve_terminate() before main so when including a certain file it becomes the new default.