Question

According to cppreference.com, std::ios_base::failure has two inheritance hierarchies:

Question

Why and what is the difference?

Background

Using g++ 4.7.1 I ran into this error and so far I know that it is because of the first inheritance hierarchy:

error: ‘const class std::ios_base::failure’ has no member named ‘code’

UPDATE

With gcc, ios_base::failure still inherits from exception even in C++11 mode. Quote from here:

ios_base::failure is not derived from system_error.

Answer 1

That’s because std::system_error was introduced in C++11. std::ios_base::failure derived directly from std::exception before.

Since the code() method is a member of std::system_error, std::ios_base::failure does not expose it in environments that do not support C++11.