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4605. Feature test macro for error_code formatting

Section: 17.3.2 [version.syn] Status: Tentatively Ready Submitter: Jonathan Wakely Opened: 2026-07-17 Last modified: 2026-09-10

Priority: Not Prioritized

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Discussion:

P3395R6 added a std::formatter specialization for error_code, but without a feature test macro. During the review of the pull request to apply the paper to the working draft there were requests for a feature test macro.

[2026-08-27; Reflector poll.]

Set status to Tentatively Ready after 9 votes in favour during reflector poll.

Proposed resolution:

This wording is relative to N5050.

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

   #define __cpp_lib_format             202603L // also in <format>
   #define __cpp_lib_format_error_code  202606L // also in <system_error>
   #define __cpp_lib_format_path        202506L // also in <filesystem>