microsoft / microsoft/STL

P3505R4 Floating-Point `to_chars()`: New Default Conversion Specifiers

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cxx29
Dominant language
C++
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Description

WG21-P3505R4 Floating-Point to_chars(): New Default Conversion Specifiers

INCREASED feature-test macro:

#define __cpp_lib_to_chars 202606L

Note: We are not yet accepting PRs for C++29 features.

As this is a (hopefully) low-impact behavioral change to an existing API (C++17's Final Boss, <charconv>) that doesn't introduce new names, we can implement this unconditionally. (Also, @jwakely mentioned that at the June 2026 meeting in Brno, he called out this paper as having been supposed to be a DR when it came up for a vote, so it should be treated as such.) However, I'd like a WP to be released with this paper applied and the feature-test macro verified, before moving this to Available.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reading the issue together with WG21-P3505R4 and the existing implementation. Identify the current floating-point to_chars defaults and the feature-test macro location, then verify the intended behavior against the published Working Paper before considering implementation or tests.

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
Quiet
Clarity
Mostly clear
Newbie friendliness
35/100

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