4440. Forward declarations of entities need also in entries

Section: 17.3.2 [version.syn] Status: WP Submitter: Tomasz Kamiński Opened: 2025-11-03 Last modified: 2025-11-11

Priority: Not Prioritized

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Discussion:

Addresses US 65-116

There are forward declarations of entities from <spanstream> and <syncstream> in <iosfwd> so their feature macros should be added to that header too. Proposed change: Add <iosfwd> to the "also in" entries for __cpp_lib_char8_t, __cpp_lib_spanstream, and __cpp_lib_syncbuf.

[Kona 2025-11-04; approved by LWG. Status changed: New → Immediate.]

[Kona 2025-11-08; Status changed: Immediate → WP.]

Proposed resolution:

This wording is relative to N5014.

  1. Modify 17.3.2 [version.syn] as indicated:

    #define __cpp_lib_char8_t                           201907L
  // freestanding, also in <atomic>, <filesystem>, <iosfwd>, <istream>, <limits>, <locale>, <ostream>, <string>,
  // <string_view>
[…]
#define __cpp_lib_spanstream                        202106L // also in <iosfwd>, <spanstream>
[…]
#define __cpp_lib_syncbuf                           201803L // also in <iosfwd>, <syncstream>