std::time_g...do_get_year(3)

🌸 NAME 🌸

okay so this is std::time_g...do_get_year(3) from the C++ Standard Libary manual page (yes, the header spells it “Libary” and we’re keeping that, bestie 💅). The actual name is:

• std::time_get::get_year,std::time_get::do_get_year — std::time_get::get_year,std::time_get::do_get_year

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✨ Synopsis ✨

Defined in header <locale>
public:

iter_type get_year( iter_type s, iter_type end, std::ios_base& str,
(1)

                    std::ios_base::iostate& err, std::tm* t ) const;
protected:

virtual iter_type do_get_year( iter_type s, iter_type end,
std::ios_base& str,  (2)

                               std::ios_base::iostate& err, std::tm*
t ) const;

1. (1) Public member function, calls the protected virtual member function do_get_year of the most derived class.
2. (2) Reads successive characters from the sequence [beg, end) and parses out the year using some implementation-defined format. Depending on the locale, two-digit years may be accepted, and it is implementation-defined which century they belong to.

The parsed year is stored in the std::tm structure field t->tm_year.

If the end iterator is reached before a valid year is read, the function sets std::ios_base::eofbit in err. If a parsing error is encountered, the function sets std::ios_base::failbit in err.

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🎀 Parameters 🎀

• beg — iterator designating the start of the sequence to parse
• end — one past the end iterator for the sequence to parse
• str — a stream object that this function uses to obtain locale facets when needed, e.g. std::ctype to skip whitespace or std::collate to compare strings
• err — stream error flags object that is modified by this function to indicate errors
• t — pointer to the std::tm object that will hold the result of this function call

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💖 Return value 💖

Iterator pointing one past the last character in [beg, end) that was recognized as a part of a valid year.

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🦋 Notes 🦋

For two-digit input values, many implementations use the same parsing rules as the conversion specifier '%y' as used by std::get_time, std::time_get::get(), and the POSIX function strptime(): two-digit integer is expected, the values in the range [69, 99] results in values 1969 to 1999, range [00, 68] results in 2000 to 2068. Four-digit inputs are typically accepted as-is.

If a parsing error is encountered, most implementations of this function leave *t unmodified.

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🌈 Example 🌈

Run this code, bestie 🏃‍♀️💨:

#include <iostream>
#include <iterator>
#include <locale>
#include <sstream>

void try_get_year(const std::string& s)
{
    std::cout << "Parsing the year out of '" << s
              << "' in the locale " << std::locale().name() << '\n';
    std::istringstream str(s);
    std::ios_base::iostate err = std::ios_base::goodbit;

    std::tm t;
    std::time_get<char> const& facet =
        std::use_facet<std::time_get<char>>(str.getloc());
    std::istreambuf_iterator<char> ret = facet.get_year({str}, {}, str, err, &t);
    str.setstate(err);
    std::istreambuf_iterator<char> last{};

    if (str)
    {
        std::cout << "Successfully parsed, year is " << 1900 + t.tm_year;

        if (ret != last)
        {
            std::cout << " Remaining content: ";
            std::copy(ret, last, std::ostreambuf_iterator<char>(std::cout));
        }
        else
            std::cout << " the input was fully consumed";
    }
    else
    {
        std::cout << "Parse failed. Unparsed string: ";
        std::copy(ret, last, std::ostreambuf_iterator<char>(std::cout));
    }

    std::cout << '\n';
}

int main()
{
    std::locale::global(std::locale("en_US.utf8"));
    try_get_year("13");
    try_get_year("2013");

    std::locale::global(std::locale("ja_JP.utf8"));
    try_get_year("2013年");
}

🍓 Possible output 🍓

Parsing the year out of '13' in the locale en_US.utf8
Successfully parsed, year is 2013 the input was fully consumed
Parsing the year out of '2013' in the locale en_US.utf8
Successfully parsed, year is 2013 the input was fully consumed
Parsing the year out of '2013年' in the locale ja_JP.utf8
Successfully parsed, year is 2013 Remaining content: 年

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💅 Defect reports 💅

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• LWG 248 — applied to C++98 — behavior as published: eofbit was not set upon reaching the end iterator — correct behavior: sets eofbit if a valid year has not been read.

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⭐ See also ⭐

• get_time — parses a date/time value of specified format (C++11) (function template)

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That’s the whole page, bestie 🫶✨ Source/version is http://cppreference.com, dated 2024.06.10, for std::time_g...do_get_year(3) — luv u, bye 💖🎀