c++ - Why Base Class catch block catch derived class object?

Question

Why does the Base catch handler catch a Derived object, as in:

#include <iostream>
using namespace std;
class Base {};
class Derived: public Base {};

int main()
{
   Derived d;
   try {
        throw d;
   }    
   catch(Base b)
   {
        cout << "Caught Base Exception";
   }    
   catch(...)
   {
       cout << "Default
";
   }
   return 0;
}

The output I get is "Caught Base Exception". I was expecting "Default".

Answer 1

Because a Derived is implicitly convertible to a Base, so when the first catch handler is tried, it succeeds. This is the same reason why we can call all the std exceptions as:

catch (std::exception const& e) {
   ..
}

Otherwise, we would have to enumerate all of them - which would be tedious at best and impossible at worst.