std::chrono...o::utc_time)(3)

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

🕰️💅 std::chrono::from_stream(std::chrono::utc_time) — C++ Standard Libary (3) 💅🕰️

okay bestie, welcome to part 1 of the std::chrono::from_stream(std::chrono::utc_time) manual page from the C++ Standard Libary. this one is all about scooping a UTC time point out of an input stream with a format string, and it is lowkey iconic. no cap. ✨

🌸 NAME 🌸

std::chrono::from_stream(std::chrono::utc_time) — std::chrono::from_stream(std::chrono::utc_time)

✨ Synopsis ✨

here’s the signature, bestie — copied exactly so nobody has to guess:

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

std::basic_istream<CharT, Traits>&
    from_stream( std::basic_istream<CharT, Traits>& is, const CharT* fmt,
(since C++20)
                 std::chrono::utc_time<Duration>& tp,
                 std::basic_string<CharT, Traits, Alloc>* abbrev = nullptr,

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

so yeah — since C++20, this overload tries to parse the input stream is into the time point tp according to the format string fmt. it’s giving “turn text into time” and honestly? obsessed. 🫶

It behaves as an UnformattedInputFunction, with one little exception: it has an unspecified effect on is.gcount(). so do not come for gcount() here, okay? 💀

After constructing and checking the sentry object, it attempts to parse the input stream is into tp according to the format string fmt.

If the parse fails to decode a valid time point, is.setstate(std::ios_base::failbit) is called and tp is not modified. periodt. no half-parsed little gremlin situation — tp stays exactly as it was. 🎀

If the format specifier %Z is used and successfully parsed, the parsed value is assigned to *abbrev if abbrev is not null.

If the format specifier %z or a modified variant is used and successfully parsed, the parsed value is assigned to *offset if offset is not null, and the parsed offset will be subtracted from the parsed timestamp before the difference is assigned to tp. yes, the math is mathing — offset gets subtracted before tp gets the result. 💅

🧾 Parameters 🧾

is — the input stream, aka the place we’re reading from.
fmt — the format string (peep the next section, bestie).
tp — the time point object that’s gonna hold the parse result.
abbrev — if it’s not null, this is 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, this is a pointer to an object that will hold the offset from UTC corresponding to the %z specifier.

🎀 Format string 🎀

Okay so the format string is made of zero or more conversion specifiers and ordinary characters. 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. No cap, that’s just how it is. 🌸

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. 😭

🧚 Conversion specifiers 🧚

The following conversion specifiers are available:

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

🌈 Year 🌈

%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 🦋

%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 🍓

%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.
%e, %Ne, %Oe — the modified commands %Od and %Oe interpret the locale’s alternative representation. 💖

⭐ Day of the week ⭐

%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 🌸

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 💜

%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 🎀

%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 💅

%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 if Duration is convertible to std::chrono::seconds, otherwise it is determined by the decimal precision of Duration and the field is interpreted as a long double in a fixed format, with the decimal point character determined by the locale (if encountered). 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 💅

Okay bestie, here are the rest of the format specifiers, and yes, every single one is relevant:

%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 parses 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 page says: is. That's it. That's the whole vibe, bestie. 😭

🎀 Example 🎀

This section is incomplete.

Reason: no example. 💀

🦋 See also 🦋

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

🌸 Category 🌸

* Todo no example 🎀

Source http://cppreference.com, version/date 2024.06.10, page std::chrono...o::utc_time)(3) — catch you later, bestie 💖✨

📦 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