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fixes #758 -- correctly document that %Y parses negative years #760

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Aug 9, 2022
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fixes #758 -- correctly document that %Y parses negative years #760

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57 changes: 27 additions & 30 deletions src/format/strftime.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,9 +11,9 @@ The following specifiers are available both to formatting and parsing.
| Spec. | Example | Description |
|-------|----------|----------------------------------------------------------------------------|
| | | **DATE SPECIFIERS:** |
| `%Y` | `2001` | The full proleptic Gregorian year, zero-padded to 4 digits. [^1] |
| `%C` | `20` | The proleptic Gregorian year divided by 100, zero-padded to 2 digits. [^2] |
| `%y` | `01` | The proleptic Gregorian year modulo 100, zero-padded to 2 digits. [^2] |
| `%Y` | `2001` | The full proleptic Gregorian year, zero-padded to 4 digits. Allows negative years. |
| `%C` | `20` | The proleptic Gregorian year divided by 100, zero-padded to 2 digits. [^1] |
| `%y` | `01` | The proleptic Gregorian year modulo 100, zero-padded to 2 digits. [^1] |
| | | |
| `%m` | `07` | Month number (01--12), zero-padded to 2 digits. |
| `%b` | `Jul` | Abbreviated month name. Always 3 letters. |
Expand All @@ -28,12 +28,12 @@ The following specifiers are available both to formatting and parsing.
| `%w` | `0` | Sunday = 0, Monday = 1, ..., Saturday = 6. |
| `%u` | `7` | Monday = 1, Tuesday = 2, ..., Sunday = 7. (ISO 8601) |
| | | |
| `%U` | `28` | Week number starting with Sunday (00--53), zero-padded to 2 digits. [^3] |
| `%U` | `28` | Week number starting with Sunday (00--53), zero-padded to 2 digits. [^2] |
| `%W` | `27` | Same as `%U`, but week 1 starts with the first Monday in that year instead.|
| | | |
| `%G` | `2001` | Same as `%Y` but uses the year number in ISO 8601 week date. [^4] |
| `%g` | `01` | Same as `%y` but uses the year number in ISO 8601 week date. [^4] |
| `%V` | `27` | Same as `%U` but uses the week number in ISO 8601 week date (01--53). [^4] |
| `%G` | `2001` | Same as `%Y` but uses the year number in ISO 8601 week date. [^3] |
| `%g` | `01` | Same as `%y` but uses the year number in ISO 8601 week date. [^3] |
| `%V` | `27` | Same as `%U` but uses the week number in ISO 8601 week date (01--53). [^3] |
| | | |
| `%j` | `189` | Day of the year (001--366), zero-padded to 3 digits. |
| | | |
Expand All @@ -52,32 +52,32 @@ The following specifiers are available both to formatting and parsing.
| `%p` | `AM` | `AM` or `PM` in 12-hour clocks. |
| | | |
| `%M` | `34` | Minute number (00--59), zero-padded to 2 digits. |
| `%S` | `60` | Second number (00--60), zero-padded to 2 digits. [^5] |
| `%f` | `026490000` | The fractional seconds (in nanoseconds) since last whole second. [^8] |
| `%.f` | `.026490`| Similar to `.%f` but left-aligned. These all consume the leading dot. [^8] |
| `%.3f`| `.026` | Similar to `.%f` but left-aligned but fixed to a length of 3. [^8] |
| `%.6f`| `.026490` | Similar to `.%f` but left-aligned but fixed to a length of 6. [^8] |
| `%.9f`| `.026490000` | Similar to `.%f` but left-aligned but fixed to a length of 9. [^8] |
| `%3f` | `026` | Similar to `%.3f` but without the leading dot. [^8] |
| `%6f` | `026490` | Similar to `%.6f` but without the leading dot. [^8] |
| `%9f` | `026490000` | Similar to `%.9f` but without the leading dot. [^8] |
| `%S` | `60` | Second number (00--60), zero-padded to 2 digits. [^4] |
| `%f` | `026490000` | The fractional seconds (in nanoseconds) since last whole second. [^7] |
| `%.f` | `.026490`| Similar to `.%f` but left-aligned. These all consume the leading dot. [^7] |
| `%.3f`| `.026` | Similar to `.%f` but left-aligned but fixed to a length of 3. [^7] |
| `%.6f`| `.026490` | Similar to `.%f` but left-aligned but fixed to a length of 6. [^7] |
| `%.9f`| `.026490000` | Similar to `.%f` but left-aligned but fixed to a length of 9. [^7] |
| `%3f` | `026` | Similar to `%.3f` but without the leading dot. [^7] |
| `%6f` | `026490` | Similar to `%.6f` but without the leading dot. [^7] |
| `%9f` | `026490000` | Similar to `%.9f` but without the leading dot. [^7] |
| | | |
| `%R` | `00:34` | Hour-minute format. Same as `%H:%M`. |
| `%T` | `00:34:60` | Hour-minute-second format. Same as `%H:%M:%S`. |
| `%X` | `00:34:60` | Locale's time representation (e.g., 23:13:48). |
| `%r` | `12:34:60 AM` | Hour-minute-second format in 12-hour clocks. Same as `%I:%M:%S %p`. |
| | | |
| | | **TIME ZONE SPECIFIERS:** |
| `%Z` | `ACST` | Local time zone name. Skips all non-whitespace characters during parsing. [^9] |
| `%Z` | `ACST` | Local time zone name. Skips all non-whitespace characters during parsing. [^8] |
| `%z` | `+0930` | Offset from the local time to UTC (with UTC being `+0000`). |
| `%:z` | `+09:30` | Same as `%z` but with a colon. |
| `%#z` | `+09` | *Parsing only:* Same as `%z` but allows minutes to be missing or present. |
| | | |
| | | **DATE & TIME SPECIFIERS:** |
|`%c`|`Sun Jul 8 00:34:60 2001`|Locale's date and time (e.g., Thu Mar 3 23:05:25 2005). |
| `%+` | `2001-07-08T00:34:60.026490+09:30` | ISO 8601 / RFC 3339 date & time format. [^6] |
| `%+` | `2001-07-08T00:34:60.026490+09:30` | ISO 8601 / RFC 3339 date & time format. [^5] |
| | | |
| `%s` | `994518299` | UNIX timestamp, the number of seconds since 1970-01-01 00:00 UTC. [^7]|
| `%s` | `994518299` | UNIX timestamp, the number of seconds since 1970-01-01 00:00 UTC. [^6]|
| | | |
| | | **SPECIAL SPECIFIERS:** |
| `%t` | | Literal tab (`\t`). |
Expand All @@ -95,24 +95,21 @@ Modifier | Description

Notes:

[^1]: `%Y`:
Negative years are allowed in formatting but not in parsing.

[^2]: `%C`, `%y`:
[^1]: `%C`, `%y`:
This is floor division, so 100 BCE (year number -99) will print `-1` and `99` respectively.

[^3]: `%U`:
[^2]: `%U`:
Week 1 starts with the first Sunday in that year.
It is possible to have week 0 for days before the first Sunday.

[^4]: `%G`, `%g`, `%V`:
[^3]: `%G`, `%g`, `%V`:
Week 1 is the first week with at least 4 days in that year.
Week 0 does not exist, so this should be used with `%G` or `%g`.

[^5]: `%S`:
[^4]: `%S`:
It accounts for leap seconds, so `60` is possible.

[^6]: `%+`: Same as `%Y-%m-%dT%H:%M:%S%.f%:z`, i.e. 0, 3, 6 or 9 fractional
[^5]: `%+`: Same as `%Y-%m-%dT%H:%M:%S%.f%:z`, i.e. 0, 3, 6 or 9 fractional
digits for seconds and colons in the time zone offset.
<br>
<br>
Expand All @@ -121,12 +118,12 @@ Notes:
stable, it is best to avoid this specifier if you want to control the exact
output.

[^7]: `%s`:
[^6]: `%s`:
This is not padded and can be negative.
For the purpose of Chrono, it only accounts for non-leap seconds
so it slightly differs from ISO C `strftime` behavior.

[^8]: `%f`, `%.f`, `%.3f`, `%.6f`, `%.9f`, `%3f`, `%6f`, `%9f`:
[^7]: `%f`, `%.f`, `%.3f`, `%.6f`, `%.9f`, `%3f`, `%6f`, `%9f`:
<br>
The default `%f` is right-aligned and always zero-padded to 9 digits
for the compatibility with glibc and others,
Expand Down Expand Up @@ -157,7 +154,7 @@ Notes:
and parsing `07`, `070000` etc. will yield the same.
Note that they can read nothing if the fractional part is zero.

[^9]: `%Z`:
[^8]: `%Z`:
Offset will not be populated from the parsed data, nor will it be validated.
Timezone is completely ignored. Similar to the glibc `strptime` treatment of
this format code.
Expand Down