Throwing std::ios_base::failure on formatted input with gcc 6.2

[Jonathan Wakely]

On 27 October 2016 at 15:30, Edward Diener
<eldlistmailingz@tropicsoft.com> wrote:
> On 10/27/2016 10:00 AM, Jonathan Wakely wrote:
>>
>> On 27 October 2016 at 14:52, Edward Diener wrote:
>>>
>>> It sounds like you are also saying that there is no way to catch the old
>>> type, even if I wanted to, since the header file declaration has the
>>> decorated attribute.
>>
>>
>> No, the attribute is only present conditionally, see
>> https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html
>>
>> If you compile with _GLIBCXX_USE_CXX11_ABI defined to zero then you
>> get the declaration of the old type (and the old COW std::string, and
>> the old std::list with O(n) size()).
>>
>
> Thanks ! IMO clearly you should be throwing the std::ios_base::failure which
> corresponds to the _GLIBCXX_USE_CXX11_ABI macro setting being used.

The exception is thrown from code inside libstdc++.so, which is
already compiled and can't be affected by a macro defined when you
#include <iostream>.

We could maybe set a thread-local variable every time an iostream
operation is performed, based on the macro value, and have the library
inspect the thread-local to decide which type to throw, but that would
be ugly, and still not always do the right thing.


> That gcc
> is throwing the the old type even when _GLIBCXX_USE_CXX11_ABI is defined as
> 1 cannot be right. But I think that is what you already said.

No, I said I'm going to change it to always throw the new type. It
will won't depend on the macro.

> What always works now is to catch std::exception rather than
> std::ios_base::failure so I will use that.
>