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### 3218. Modifier for `%d` parse flag does not match POSIX and `format` specification

Section: 27.13 [time.parse] Status: C++20 Submitter: Tomasz Kamiński Opened: 2019-06-13 Last modified: 2021-02-25

Priority: 0

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Discussion:

Currently, the '`%d`' parse flags accepts the '`E`' modifier to parse the locale's alternative representation, see Table 88 — "Meaning of `parse` flags":

> The modified command `%Ed` interprets the locale's alternative representation of the day of the month.

This is inconsistent with the POSIX `strftime` specification and the `format` functions, that uses '`O`' to output alternate locale representation. Per Table 87 — "Meaning of `format` conversion specifiers":

> The modified command `%Od` produces the locale's alternative representation.

[2019-06-24; Howard comments]

This was simply a type-o in my documentation that infected the proposal and subsequently the C++ working draft.

None of `std::time_put`, C's `strftime`, or POSIX's `strftime` support `%Ed` but all support `%Od`. Furthermore the existing example implementation supports `%Od` but not `%Ed`. And all the existing example implementation does is forward to `std::time_put`.

[2019-07 Issue Prioritization]

Status to Tentatively Ready after five positive votes on the reflector.

Proposed resolution:

This wording is relative to N4810.

1. Modify 27.13 [time.parse], Table 88 — "Meaning of `parse` flags", as indicated:

   > Table 88 — Meaning of `parse` flags
   > Flag | Parsed value
   > --- | ---
   > `[…]`
   > `%d` | The day of the month as a decimal number. The modified command `%Nd` specifies the maximum number of characters to read. If `N` is not specified, the default is 2. Leading zeroes are permitted but not required. The modified command `%EOd` interprets the locale's alternative representation of the day of the month.
   > `[…]`