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### 2087. `iostream_category()` and `noexcept`

Section: 29.5 [iostreams.base] Status: C++14 Submitter: Nicolai Josuttis Opened: 2011-09-22 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

In `<system_error>` we have:

>     const error_category& generic_category() noexcept;
>     const error_category& system_category() noexcept;

In `<future>` we have:

>     const error_category& future_category() noexcept;

But in `<ios>` we have:

>     const error_category& iostream_category();

Is there any reason that `iostream_category()` is not declared with `noexcept` or is this an oversight?

Daniel:

This looks like an oversight to me. We made the above mentioned changes as part of noexcept-ifying the thread library but `iostream_category()` was skipped, so it seems to be forgotten. There should be no reason, why it cannot be `noexcept`. When doing so, we should also make these functions `noexcept` (similar to corresponding overloads):

>     error_code make_error_code(io_errc e);
>     error_condition make_error_condition(io_errc e);

Suggested wording provided by Daniel.

[2013-04-20, Bristol]

Unanimous.

Resolution: move to tentatively ready.

[2013-09-29, Chicago]

Apply to Working Paper

Proposed resolution:

This wording is relative to the FDIS.

1. Change [iostreams.base.overview], header `<ios>` synopsis as indicated:

   >     #include <iosfwd>
   >     namespace std {
   >       […]
   >       error_code make_error_code(io_errc e) noexcept;
   >       error_condition make_error_condition(io_errc e) noexcept;
   >       const error_category& iostream_category() noexcept;
   >     }

2. Change the prototype declarations in 29.5.6 [error.reporting] as indicated:

   >     error_code make_error_code(io_errc e) noexcept;

   > -1- Returns: `error_code(static_cast<int>(e), iostream_category())`.

   >     error_condition make_error_condition(io_errc e) noexcept;

   > -2- Returns: `error_condition(static_cast<int>(e), iostream_category())`.

   >     const error_category& iostream_category() noexcept;

   > -3- Returns: A reference to an object of a type derived from class `error_category`.

   > -4- The object’s `default_error_condition` and `equivalent` virtual functions shall behave as specified for the class `error_category`. The object’s `name` virtual function shall return a pointer to the string `"iostream"`.