microsoft / microsoft/STL

P3391R2 `constexpr` `std::format`

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cxx26 format
Dominant language
C++
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Description

WG21-P3391R2 constexpr std::format
LWG-4531 Should there be a feature-test macro update for constexpr std::to_(w)string?

Feature-test macro:

#define __cpp_lib_constexpr_format 202511L

INCREASED feature-test macro:

#define __cpp_lib_constexpr_string 202511L

Note: We are not yet accepting PRs for C++26 features.

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Research direction

Read WG21-P3391R2 and LWG-4531 first; the issue identifies the proposed constexpr formatting work and the __cpp_lib_constexpr_format and __cpp_lib_constexpr_string macros. There are no files or tests named, and the issue states that PRs for C++26 features are not yet being accepted.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
backend-api-design
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
20/100

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