Proposed resolution:
This wording is relative to N4917.
[Drafting Note: Two mutually exclusive options are prepared, depicted below by Option A and Option B, respectively.]
Option A: This is Howard Hinnant's choice (3)
Modify [time.format], Table [tab:time.format.spec] as indicated:
Table 102 — Meaning of conversion specifiers [tab:time.format.spec] Specifier Replacement […] %y The last two decimal digits of the yearremainder after dividing the year by 100 using floored division.
If the result is a single digit it is prefixed by 0.
The modified command %Oy produces the locale's alternative representation. The
modified command %Ey produces the locale's alternative representation of offset from
%EC (year only).[…]
Modify [time.parse], Table [tab:time.parse.spec] as indicated:
Table 103 — Meaning of parse flags [tab:time.parse.spec] Flag Parsed value […] %y The last two decimal digits of the yearremainder after dividing the year by 100 using floored division.
If the century is not otherwise specified (e.g.
with %C), values in the range [69, 99] are presumed to refer to the years 1969 to 1999,
and values in the range [00, 68] are presumed to refer to the years 2000 to 2068. The
modified command %N y 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 commands %Ey and %Oy interpret the locale's alternative representation.[…]
Option B: This is Howard Hinnant's choice (1)
Modify [time.format], Table [tab:time.format.spec] as indicated:
Table 102 — Meaning of conversion specifiers [tab:time.format.spec] Specifier Replacement […] %y The last two decimal digits of the year, regardless of the sign of the year.
If the result is a single digit it is prefixed by 0.
The modified command %Oy produces the locale's alternative representation. The
modified command %Ey produces the locale's alternative representation of offset from
%EC (year only).
[Example ?: cout << format("{:%C %y}", -1976y); prints -20 76. — end example][…]
Modify [time.parse], Table [tab:time.parse.spec] as indicated:
Table 103 — Meaning of parse flags [tab:time.parse.spec] Flag Parsed value […] %y The last two decimal digits of the year, regardless of the sign of the year.
If the century is not otherwise specified (e.g.
with %C), values in the range [69, 99] are presumed to refer to the years 1969 to 1999,
and values in the range [00, 68] are presumed to refer to the years 2000 to 2068. The
modified command %N y 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 commands %Ey and %Oy interpret the locale's alternative representation.
[Example ?: year y; istringstream{"-20 76"} >> parse("%3C %y", y); results in
y == -1976y. — end example][…]