Issue 4022 - WG21 LWG Issues
Title
Ambiguity in the formatting of negative years with format specifier %C
Status
new
Section
[time.format]
Submitter
Jiang An

Created on 2023-12-08.00:00:00 last changed 7 days ago

Messages

msg15215 (view)
Date: 2025-10-17.13:06:28

Proposed resolution:

This wording is relative to N5014.

  1. Modify [time.format], Table 133 [tab:time.format.spec], as indicated:

    Table 133 — Meaning of conversion specifiers [tab:time.format.spec]
    Specifier Replacement
    […]
    %C The year divided by 100 using floored division. If the result is a single decimal digit, it
    is prefixed with 0
    in the range [-9, 9] then 0 is inserted before the single digit (after the sign, if present).
    The modified command %EC produces the locale's alternative
    representation of the century.
    […]
msg15210 (view)
Date: 2025-10-15.00:00:00

[ 2025-10-17; Jonathan provides new wording based on Option B ]
msg13886 (view)
Date: 2025-10-15.00:00:00

[ 2025-10-17; Reflector poll. ]

Set priority to 3 after reflector poll.

Howard intended Option B, i.e. `"-09"`, but Option B could possibly be interpreted to mean `"0-9"`. "Maybe something like the 0 is inserted before the sole digit, or after the sign, if any."

This wording is relative to N4964.

[Drafting Note: Two mutually exclusive options are prepared, depicted below by Option A and Option B, respectively.]

Option A:

  1. Modify [time.format], Table 101 [tab:time.format.spec], as indicated:

    Table 101 — Meaning of conversion specifiers [tab:time.format.spec]
    Specifier Replacement
    […]
    %C The year divided by 100 using floored division. If the result is a single decimal digitin range [0, 9], it
    is prefixed with 0. The modified command %EC produces the locale's alternative
    representation of the century.
    […]

Option B:

  1. Modify [time.format], Table 101 [tab:time.format.spec], as indicated:

    Table 101 — Meaning of conversion specifiers [tab:time.format.spec]
    Specifier Replacement
    […]
    %C The year divided by 100 using floored division. If the result is a single decimal digitin range [-9, 9], it
    is prefixed with 0. The modified command %EC produces the locale's alternative
    representation of the century.
    […]
msg13885 (view)
Date: 2023-12-08.00:00:00

Table 101, [tab:time.format.spec] reads:

Table 101 — Meaning of conversion specifiers [tab:time.format.spec]
Specifier Replacement
[…]
%C The year divided by 100 using floored division. If the result is a single decimal digit, it
is prefixed with 0. The modified command %EC produces the locale's alternative
representation of the century.
[…]

When the year is in range [-99, -10], it is unclear whether the result (in range [-9, -1]) is considered as a single decimal digit, and there is implementation divergence (llvm/llvm-project#74727).

Daniel:

This issue is somewhat related to LWG 3831.

History
Date User Action Args
2025-10-17 13:06:28adminsetmessages: + msg15215
2025-10-17 12:42:49adminsetmessages: + msg15210
2023-12-09 16:07:14adminsetmessages: + msg13886
2023-12-08 00:00:00admincreate