std::time_get::get, std::time_get::do_get - cppreference.com

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# std::time_get::get, std::time_get::do_get

From cppreference.com
< cpp‎ | locale‎ | time get

Defined in header `<locale>` |  |
public: iter_type get(iter_type beg, iter_type end, std::ios_base& str, std::ios_base::iostate& err, std::tm* t, const char_type* fmtbeg, const char_type* fmtend) const; | (1) | (since C++11)
protected: virtual iter_type do_get(iter_type neg, iter_type end, std::ios_base& str, std::ios_base::iostate& err, std::tm *t, char format, char modifier) const; | (2) | (since C++11)

1) Parses the date and time from the input character sequence `[beg, end)` according to the format provided in the character sequence [fmtbeg, fmtend). The format is expected to follow the format described below, although actual processing of each format specifier can be customized by overriding `do_get`. The `get` function performs the following: First, clears the error bits in `err` by executing err = std::ios_base::goodbit. Then enters a loop, which terminates whenever any of the following conditions becomes true (checked in this order):
a) All characters have been read from the format string (fmtbeg == fmtend)
b) There was a parsing error (err != std::ios_base::goodbit)
c) All characters have been read from the input sequence (beg == end. If this condition terminates the loop, the function sets both `eofbit` and `failbit` in `err`

    In the body of the loop, the following steps take place:

a) if the next character in the format string is '%', followed by one or two characters that form a valid std::get_time conversion specifier (see below), these characters are used in the call do_get(beg, end, str, err, t, format, modifier), where `format` is the primary conversion specifier character, and `modifier` is the optional modifier (which appears between `%` and the format character, if present). If there is no modifier, the value '\0' is used. If the format string is ambiguous or ends too early to determine the conversion specifier after '%', `eofbit` is set in `err` and the loop is terminated. If, after the call to `do_get`, no error bits are set in `err`, the function increments `fmtbeg` to point right after the conversion specifier and continues the loop.
b) If the next character is whitespace, as indicated by the locale provided in the stream `str` (i.e. std::isspace(*fmtbeg, str.getloc()) == true, the function keeps incrementing `fmtbeg` until it either becomes equal to `fmtend` or points to a non-whitespace character.
c) If the next character in the format string is equivalent to the next character in the input stream according to case-insensitive comparison, the function advances both sequences by one character ++fmtbeg, ++beg; and continues the loop, Otherwise, it sets the `failbit` in `err`.
2) Parses one conversion specifier from the input sequence `[beg, end)` and updates the std::tm structure pointed to by `t` accordingly.

    First, clears the error bits in `err` by executing err = std::ios_base::goodbit. Then reads characters from the input sequence `[beg, end)` that are expected by the std::time_get format specifier formed by combining '%', `modifier` (if not '\0'), and `format`. If the characters do not combine to form a valid conversion specifier, sets `failbit` in `err`. If the end of the input stream is reached after reading a character, sets `eofbit` in `err`. If the input string was parsed successfully, updates the corresponding fields of *t.

    For complex conversion specifiers, such as '%x' or '%c', or the directives that use the modifiers 'E' and 'O', the function may fail to determine some of the values to store in *t. In such case, it sets `eofbit` in `err` and leaves these fields in unspecified state.

### [edit] 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
fmtbeg | - | pointer to the first character of a sequence of char_type characters specifying the conversion format The format string consists of zero or more conversion specifiers, whitespace characters, and ordinary characters (except `%`). Each ordinary character is expected to match one character in the input stream in case-insensitive comparison. Each whitespace character matches arbitrary whitespace in the input string. Each conversion specification begins with `%` character, optionally followed by `E` or `O` modifier (ignored if unsupported by the locale), followed by the character that determines the behavior of the specifier. The format specifiers match the POSIX function strptime():
Conversion specifier | Explanation | Writes to fields
--- | --- | ---
`%` | matches a literal `%`. The full conversion specification must be `%%`. | (none)
`t` | matches any whitespace. | (none)
`n` | matches any whitespace. | (none)
Year
`Y` | parses full year as a 4 digit decimal number, leading zeroes permitted but not required | `tm_year`
`EY` | parses year in the alternative representation, e.g.平成23年 (year Heisei 23) which writes 2011 to tm_year in ja_JP locale | `tm_year`
`y` | parses last 2 digits of year as a decimal number. Range `[69,99]` results in values 1969 to 1999, range `[00,68]` results in 2000-2068 | `tm_year`
`Oy` | parses last 2 digits of year using the alternative numeric system, e.g. 十一 is parsed as 11 in ja_JP locale | `tm_year`
`Ey` | parses year as offset from locale's alternative calendar period `%EC` | `tm_year`
`C` | parses the first 2 digits of year as a decimal number (range `[00,99]`) | `tm_year`
`EC` | parses the name of the base year (period) in the locale's alternative representation, e.g. 平成 (Heisei era) in ja_JP | `tm_year`
Month
`b` | parses the month name, either full or abbreviated, e.g. `Oct` | `tm_mon`
`h` | synonym of `b` | `tm_mon`
`B` | synonym of `b` | `tm_mon`
`m` | parses the month as a decimal number (range `[01,12]`), leading zeroes permitted but not required | `tm_mon`
`Om` | parses the month using the alternative numeric system, e.g. 十二 parses as 12 in ja_JP locale | `tm_mon`
Week
`U` | parses the week of the year as a decimal number (Sunday is the first day of the week) (range `[00,53]`), leading zeroes permitted but not required | `tm_year`, `tm_wday`, `tm_yday`
`OU` | parses the week of the year, as by `%U`, using the alternative numeric system, e.g. 五十二 parses as 52 in ja_JP locale | `tm_year`, `tm_wday`, `tm_yday`
`W` | parses the week of the year as a decimal number (Monday is the first day of the week) (range `[00,53]`), leading zeroes permitted but not required | `tm_year`, `tm_wday`, `tm_yday`
`OW` | parses the week of the year, as by `%W`, using the alternative numeric system, e.g. 五十二 parses as 52 in ja_JP locale | `tm_year`, `tm_wday`, `tm_yday`
Day of the year/month
`j` | parses day of the year as a decimal number (range `[001,366]`), leading zeroes permitted but not required | `tm_yday`
`d` | parses the day of the month as a decimal number (range `[01,31]`), leading zeroes permitted but not required | `tm_mday`
`Od` | parses the day of the month using the alternative numeric system, e.g 二十七 parses as 27 in ja_JP locale, leading zeroes permitted but not required | `tm_mday`
`e` | synonym of `d` | `tm_mday`
`Oe` | synonym of `Od` | `tm_mday`
Day of the week
`a` | parses the name of the day of the week, either full or abbreviated, e.g. `Fri` | `tm_wday`
`A` | synonym of `a` | `tm_wday`
`w` | parses weekday as a decimal number, where Sunday is `0` (range `[0-6]`) | `tm_wday`
`Ow` | parses weekday as a decimal number, where Sunday is `0`, using the alternative numeric system, e.g. 二 parses as 2 in ja_JP locale | `tm_wday`
Hour, minute, second
`H` | parses the hour as a decimal number, 24 hour clock (range `[00-23]`), leading zeroes permitted but not required | `tm_hour`
`OH` | parses hour from 24-hour clock using the alternative numeric system, e.g. 十八 parses as 18 in ja_JP locale | `tm_hour`
`I` | parses hour as a decimal number, 12 hour clock (range `[01,12]`), leading zeroes permitted but not required | `tm_hour`
`OI` | parses hour from 12-hour clock using the alternative numeric system, e.g. 六 reads as 06 in ja_JP locale | `tm_hour`
`M` | parses minute as a decimal number (range `[00,59]`), leading zeroes permitted but not required | `tm_min`
`OM` | parses minute using the alternative numeric system, e.g. 二十五 parses as 25 in ja_JP locale | `tm_min`
`S` | parses second as a decimal number (range `[00,60]`), leading zeroes permitted but not required | `tm_sec`
`OS` | parses second using the alternative numeric system, e.g. 二十四 parses as 24 in ja_JP locale | `tm_sec`
Other
`c` | parses the locale's standard date and time string format, e.g. `Sun Oct 17 04:41:13 2010` (locale dependent) | all
`Ec` | parses the locale's alternative date and time string format, e.g. expecting 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale | all
`x` | parses the locale's standard date representation | all
`Ex` | parses the locale's alternative date representation, e.g. expecting 平成23年 (year Heisei 23) instead of 2011年 (year 2011) in ja_JP locale | all
`X` | parses the locale's standard time representation | all
`EX` | parses the locale's alternative time representation | all
`D` | equivalent to "%m / %d / %y " | `tm_mon`, `tm_mday`, `tm_year`
`r` | parses locale's standard 12-hour clock time (in POSIX, "%I : %M : %S %p") | `tm_hour`, `tm_min`, `tm_sec`
`R` | equivalent to "%H : %M" | `tm_hour`, `tm_min`
`T` | equivalent to "%H : %M : %S" | `tm_hour`, `tm_min`, `tm_sec`
`p` | parses the locale's equivalent of a.m. or p.m. | `tm_hour`
Note: `tm_isdst` is not written to, and needs to be set explicitly for use with functions such as `mktime`
fmtend | - | pointer one past the last character of a sequence of char_type characters specifying the conversion format
format | - | the character that names a conversion specifier
modifier | - | the optional modifier that may appear between `%` and the conversion specifier

### [edit] Return value

Iterator pointing one past the last character in `[beg, end)` that was parsed successfully.

### [edit] Notes

The case-insensitive comparison for the non-whitespace non-'%' characters in the format string, the std::collate facet of the locale provided by `str` is typically, but not necessarily, used.

If a parsing error is encountered, many implementations of this function leave `*t` completely untouched.

It's unspecified if these functions zero out the fields in *t that they do not set directly: portable programs should initialize every field to zero before calling `get()`.

### [edit] Example

Run this code

    #include <iostream>
    #include <sstream>
    #include <locale>
    #include <iomanip>

    int main()
    {
        std::istringstream ss("2011-Februar-18 23:12:34");
        ss.imbue(std::locale("de_DE"));

        auto& f = std::use_facet<std::time_get<char>>(std::locale("de_DE"));
        std::tm t{};
        std::string s = "%Y-%b-%d %H:%M:%S";
        std::ios_base::iostate err = std::ios_base::goodbit;
        std::istreambuf_iterator<char> ret = f.get(std::istreambuf_iterator<char>(ss),
                                                   std::istreambuf_iterator<char>(),
                                                   ss, err, &t, &s[0], &s[0] + s.size());
        ss.setstate(err);

        if(ss) {
            std::cout << "Successfully parsed as " << std::put_time(&t, "%c");
            if(ret != std::istreambuf_iterator<char>()) {
                std::cout << " Remaining content: ";
                std::copy(ret, std::istreambuf_iterator<char>(),
                               std::ostreambuf_iterator<char>(std::cout));
            } else {
                    std::cout << " The input was fully consumed";
            }
        } else {
                std::cout << "Parse failed. Unparsed string: ";
                std::copy(ret, std::istreambuf_iterator<char>(),
                               std::ostreambuf_iterator<char>(std::cout));
        }
        std::cout << '\n';
    }

Output:

    Successfully parsed, as Sun Feb 18 23:12:34 2011 The input was fully consumed

### [edit] See also

get_time (C++11) | parses a date/time value of specified format (function template) [edit]

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