std::time_g...do_get_date(3)

💖 std::time_get::get_date, std::time_get::do_get_date 💖

Bestie, welcome to the std::time_g...do_get_date(3) page from the C++ Standard Libary manual. Yes, date parsing, and it's lowkey a whole vibe. Let's get into it. ✨

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🎀 NAME 🎀

The page name is exactly:

std::time_get::get_date,std::time_get::do_get_date - std::time_get::get_date,std::time_get::do_get_date

So we're talking about std::time_get::get_date and std::time_get::do_get_date, together, as one iconic little duo. 💅

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🌸 Synopsis 🌸

Defined in header <locale>
public:

iter_type get_date( iter_type beg, iter_type end, std::ios_base& str,
std::ios_base::iostate& err, std::tm* t ) const;
protected:

virtual iter_type do_get_date( iter_type beg, iter_type end,
std::ios_base& str,
std::ios_base::iostate& err, std::tm* t ) const;

• (1) — this is the public member function, and it calls the protected virtual member function do_get_date of the most derived class.
• (2) — this one reads successive characters from the sequence [beg, end) and parses out the calendar date value using the default format expected by this locale, which is determined as:
• no_order → "%m/%d/%y"
• dmy → "%d/%m/%y"
• mdy → "%m/%d/%y"
• ymd → "%y/%m/%d"
• ydm → "%y/%d/%m"

These are as used by the functions std::get_time(), get(), and the POSIX function strptime(). The parsed date is stored in the corresponding fields of the std::tm structure pointed to by the argument t.

If the end iterator is reached before a valid date 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 date.

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🧚 Notes 🧚

For the alphabetic components of the default date format (if any), this function is usually case-insensitive.

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

The implementation may support other date formats besides the ones required by the standard.

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👑 Example 👑

// Run this code

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

void try_get_date(const std::string& s)
{
    std::cout << "Parsing the date 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;
    const std::time_get<char>& facet =
       std::use_facet<std::time_get<char>>(str.getloc());
    std::istreambuf_iterator<char> ret = facet.get_date({str}, {}, str,
       err, &t);
    str.setstate(err);

    if (str)
    {
        std::cout << "Day: " << t.tm_mday << ' '
                  << "Month: " << t.tm_mon + 1 << ' '
                  << "Year: " << t.tm_year + 1900 << '\n';
    }
    else
    {
        std::cout << "Parse failed. Unparsed string: ";
        std::copy(ret, {}, std::ostreambuf_iterator<char>(std::cout));
        std::cout << '\n';
    }
}
int main()
{
    std::locale::global(std::locale("en_US.utf8"));
    try_get_date("02/01/2013");
    try_get_date("02-01-2013");

    std::locale::global(std::locale("ja_JP.utf8"));
    try_get_date("2013年02月01日");
}

🌟 Output 🌟

Parsing the date out of '02/01/2013' in the locale en_US.utf8
Day: 1 Month: 2 Year: 2013
Parsing the date out of '02-01-2013' in the locale en_US.utf8
Parse failed. Unparsed string: -01-2013
Parsing the date out of '2013年02月01日' in the locale ja_JP.utf8
Day: 1 Month: 2 Year: 2013

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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 date has not been read.
• LWG 461 — Applied to: C++98. Behavior as published: do_get_date needed to parse localized date representation. Correct behavior: parses with the format determined by date_order().

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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: http://cppreference.com, version/date: 2024.06.10, page: std::time_g...do_get_date(3). Mwah. 💋