Proposed resolution:

This wording is relative to n4928.

1. Modify [iostream.objects.overview]p5 as indicated:

   -5- The results of including <iostream> in a translation unit shall be as if <iostream> defined an instance of ios_base::Init with static storage duration. Each C++ library module ([std.modules]) in a hosted implementation shall behave as if it contains an interface unit that defines an unexported ios_base::Init variable with ordered initialization ([basic.start.dynamic]).

   [Note ?: As a result, the definition of that variable is appearance-ordered before any declaration following the point of importation of a C++ library module. Whether such a definition exists is unobservable by a program that does not reference any of the standard iostream objects. — end note]

[ 2023-02-13 Approved at February 2023 meeting in Issaquah. Status changed: Immediate → WP. ]

[ Issaquah 2023-02-09; LWG ]

Move to Immediate for C++23

[ 2023-02-09 Tim updates wording following LWG discussion ]

In the old world, #include <iostream> behaves as if it defined a static-storage-duration ios_base::Init object, which causes the standard iostreams objects to be initialized (if necessary) on startup and flushed on shutdown.

But we don't include headers with import std;, so we need separate wording to provide this guarantee. The proposed resolution below was adapted from a suggestion by Mathias Stearn on the reflector.