std::chrono...hrono::year)(3)

📦 version 2024.07.05, in nixpkgs unstable, opensuse-leap 16.0

👑 C++ Standard Library 👑 — a lil page about `std::chrono::from_stream(std::chrono::year)`

okay so bestie, welcome to the group chat. this is the manual page for std::chrono::from_stream(std::chrono::year), straight out of the C++ Standard Library, and it's giving "niche but iconic." part 1 of 3, so buckle up — more coming after this, no sign-off, we're not done yet 💅

✨ NAME ✨

std::chrono::from_stream(std::chrono::year) — like, that's the whole name, twice, because the manpage said it twice and I would never gatekeep a single crumb of info from you 🫶

std::chrono::from_stream(std::chrono::year)

🌸 Synopsis 🌸

so first things first, it lives here:

Defined in header <chrono>

and the template situation is this, literally copy-paste it exactly, don't freestyle:

template< class CharT, class Traits, class Alloc = std::allocator<CharT> >

std::basic_istream<CharT, Traits>&
    from_stream( std::basic_istream<CharT, Traits>& is, const CharT* fmt,
                 std::chrono::year& y,
                 std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,

                 std::chrono::minutes* offset = nullptr );

(since C++20) — yes queen, she's a modern girlie ✨

🦋 okay but what does it DO 🦋

So basically: it attempts to parse the input stream is into the std::chrono::year y, according to the format string fmt. that's the whole vibe. parse → year → slay.

It behaves as an UnformattedInputFunction, except — and this is the important lil caveat — it has an unspecified effect on is.gcount(). like, don't count on gcount, bestie, it's not that kind of function 🙈

After constructing and checking the sentry object, it attempts to parse the input stream is into y according to the format string fmt. and if the parse fails to decode a valid year? tragic. is.setstate(std::ios_base::failbit) gets called and y is not modified. so your year stays exactly where it was, untouched, unbothered, main character energy 💀

🎀 the `%Z` and `%z` situation 🎀

this part is lowkey the most important, so pay attention 🔥

If the format specifier %Z is used and successfully parsed, the parsed value is assigned to *abbrev — but only if abbrev is not null. no abbrev, no assign. simple as.
If the format specifier %z or a modified variant is used and successfully parsed, the parsed value is assigned to *offset — but only if offset is not null. same rules, bestie.

⚠️ reminder: "if abbrev is not null" and "if offset is not null" are doing a LOT of heavy lifting in those sentences. the default for both is nullptr, so if you don't pass them, nothing gets written. periodt.

k that's part 1, more coming, don't go anywhere 💖🧚

💖 Parameters 💖

okay bestie, here’s the whole intake list — no cap, every single one:

is — an input stream 💅
fmt — a format string (peep the next section 👀)
y — the object that holds the parse result
abbrev — if it’s not null, a pointer to an object that will hold the time zone abbreviation or name corresponding to the %Z specifier
offset — if it’s not null, a pointer to an object that will hold the offset from UTC corresponding to the %z specifier

🎀 Format string 🎀

The format string is literally zero or more conversion specifiers plus ordinary characters. It’s giving build-your-own-parser, and honestly? iconic.

Each ordinary character — excluding whitespace characters and the terminating null character — matches one identical character from the input stream, or causes the function to fail if the next character on the stream does not compare equal.
Each whitespace character matches zero or more whitespace characters in the input stream.
Each unmodified conversion specifier begins with a % character followed by a character that determines the behavior of the specifier.
Some conversion specifiers have a modified form in which an E or O modifier character is inserted after the % character.
Some conversion specifiers have a modified form in which a width parameter given as a positive decimal integer (shown as N below) is inserted after the % character.
Each conversion specifier causes the matched characters to be interpreted as parts of date and time types according to the table below.

A character sequence in the format string that begins with a % but does not match one of the conversion specifiers below is interpreted as ordinary characters. slay, it just vibes as text.

🚨 If from_stream fails to parse everything specified by the format string, or if insufficient information is parsed to specify a complete result, or if parsing discloses contradictory information, is.setstate(std::ios_base::failbit) is called.

✨ The conversion specifiers ✨

%% — matches a literal % character.
%n — matches one whitespace character.
%t — matches zero or one whitespace character.

Year era 👑

%C, %NC, %EC — parses the century as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %EC interprets the locale’s alternative representation of the century.
%y, %Ny, %Ey, %Oy — parses the last two decimal digits 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 width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified commands %Ey and %Oy interpret the locale’s alternative representation.
%Y, %NY, %EY — parses the year as a decimal number. The width N specifies the maximum number of characters to read. The default width is 4. Leading zeroes are permitted but not required. The modified command %EY interprets the locale’s alternative representation.

Month moment 🌸

%b, %B, %h — parses the locale’s full or abbreviated case-insensitive month name.
%m, %Nm, %Om — parses the month as a decimal number (January is 1). The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %Om interprets the locale’s alternative representation.

Day energy 🍓

%d, %Nd, %Od — parses the day of month as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %Od interprets the locale’s alternative representation.
%e, %Ne, %Oe — these sit in the day-of-month group too. The modified commands %Od and %Oe interpret the locale’s alternative representation.

Day of the week files 🗓️

%a, %A — parses the locale’s full or abbreviated case-insensitive weekday name.
%u, %Nu — parses the ISO weekday as a decimal number (1-7), where Monday is 1. The width N specifies the maximum number of characters to read. The default width is 1. Leading zeroes are permitted but not required.
%w, %Nw, %Ow — parses the weekday as a decimal number (0-6), where Sunday is 0. The width N specifies the maximum number of characters to read. The default width is 1. Leading zeroes are permitted but not required. The modified command %Ow interprets the locale’s alternative representation.

ISO 8601 week-based year, periodt 🦋

In ISO 8601 weeks begin with Monday and the first week of the year must satisfy the following requirements:

Includes January 4
Includes first Thursday of the year

%g, %Ng — parses the last two decimal digits of the ISO 8601 week-based year. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required.
%G, %NG — parses the ISO 8601 week-based year as a decimal number. The width N specifies the maximum number of characters to read. The default width is 4. Leading zeroes are permitted but not required.
%V, %NV — parses the ISO 8601 week of the year as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required.

Week/day of the year vibes 🌈

%j, %Nj — parses the day of the year as a decimal number (January 1 is 1). The width N specifies the maximum number of characters to read. The default width is 3. Leading zeroes are permitted but not required.
%U, %NU, %OU — parses the week number of the year as a decimal number. The first Sunday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OU interprets the locale’s alternative representation.
%W, %NW, %OW — parses the week number of the year as a decimal number. The first Monday of the year is the first day of week 01. Days of the same year prior to that are in week 00. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OW interprets the locale’s alternative representation.

Date section, we’re so back 💅

%D — equivalent to "%m/%d/%y".
%F, %NF — equivalent to "%Y-%m-%d". If the width is specified, it is only applied to the %Y.
%x, %Ex — parses the locale’s date representation. The modified command %Ex interprets the locale’s alternate date representation.

Time of day, main character energy ⏰

%H, %NH, %OH — parses the hour (24-hour clock) as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OH interprets the locale’s alternative representation.
%I, %NI, %OI — parses the hour (12-hour clock) as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OI interprets the locale’s alternative representation.
%M, %NM, %OM — parses the minute as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OM interprets the locale’s alternative representation.
%S, %NS, %OS — parses the second as a decimal number. The width N specifies the maximum number of characters to read. The default width is 2. Leading zeroes are permitted but not required. The modified command %OS interprets the locale’s alternative representation.
%p — parses the locale’s equivalent of the AM/PM designations associated with a 12-hour clock.
%R — equivalent to "%H:%M".
%T — equivalent to "%H:%M:%S".
%r — parses the locale’s 12-hour clock time.
%X, %EX — parses the locale’s time representation. The modified command %EX interprets the locale’s alternate time representation.

🌈 Miscellaneous 🌈

These format-command besties are all about parsing date/time vibes, and every little character matters 💅

%c — Parses the locale's date and time representation. 🗓️
%Ec — The modified command %Ec interprets the locale's alternative date and time representation. ✨
%z — Parses the offset from UTC in the format [+|-]hh[mm]. For example, -0430 refers to 4 hours 30 minutes behind UTC, and 04 refers to 4 hours ahead of UTC. ⏰
%Ez, %Oz — The modified commands %Ez and %Oz parse the format [+|-]h[h][:mm] — i.e., requiring a : between the hours and minutes and making the leading zero for hour optional. 🫶
%Z — Parses the time zone abbreviation or name, taken as the longest sequence of characters that only contains the characters A through Z, a through z, 0 through 9, -, +, _, and /. 🌍

💖 Return value 💖

The return-value situation is literally just:

is

That's the whole thing, bestie — no extra lore in this part 😭

🦋 See also 🦋

parse — parses a chrono object from a stream (C++20) (function template). 👑

Okay, part 3 wrap-up time 💅 Big source shoutout to cppreference.com, version/date 2024.06.10, and the footer vibe std::chrono...hrono::year)(3) — mwah 💖🎀

📦 where this page comes from

nixpkgs unstable: stdman 2024.07.05
opensuse-leap 16.0: stdman 2024.07.05-bp160.1.9 · MIT
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-04: a language model's rewrite of the original, under its terms