What's the need for special exception classes?

Question

Why did the C++ standard bother inventing the std::exception classes? What's their benefit? My reason for asking is this:

try
{
  throw std::string("boom");
}
catch (std::string str)
{
  std::cout << str << std::endl;
}

Works fine. Later, if I need, I can just make my own lightweight "exception" types. So why should I bother with std::exception?

Answer 1

Why did the C++ standard bother inventing the std::exception classes? What's their benefit?

It provides a generic and consistent interface to handle exceptions thrown by the standard library. All the exceptions generated by the standard library are inherited from std::exception.

Note that standard library api's can throw a number of different kinds of exceptions, To quote a few examples:

• std::bad_alloc
• std::bad_cast
• std::bad_exception
• std::bad_typeid
• std::logic_error
• std::runtime_error
• std::bad_weak_ptr | C++11
• std::bad_function_call | C++11
• std::ios_base::failure | C++11
• std::bad_variant_access | C++17

and so on...
std::exception is the base class for all these exceptions:

providing a base class for all these exceptions, allows you to handle multiple exceptions with a common exception handler.

---

If I need, I can just make my own lightweight "exception" types. So why should I bother with std::exception?

If you need your custom exception class go ahead and make one. But std::exception makes your job easier because it already provides a lot of functionality which a good exception class should have. It provides you the ease of deriving from it and overidding necessary functions(in particular std::exception::what()) for your class functionality.
This gives you 2 advantages the std::exception handler,

• can catch standard library exceptions as well as
• exceptions of the type of your custom exception class

^{Image courtesy: http://en.cppreference.com/w/cpp/error/exception}