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weekday class

  • Artikkeli

Represents a day of the week in the Gregorian calendar. For example, Tuesday.

Syntax

class weekday; // C++20

Remarks

A weekday can hold a value of [0, 255], but typically holds a value [0, 6] to represent a day of the week. See Weekday constants, below, for constants that you can use with the weekday class.

Members

Name Description
Constructors Construct a weekday.
c_encoding Get the weekday value.
iso_encoding Get the ISO 8601 weekday value.
ok Check if the weekday value is valid.
operator++ Increment the weekday.
operator+= Add the specified number of weekdays to this weekday.
operator-- Decrement the weekday.
operator-= Subtract the specified number of weekdays from this weekday.
operator[] Create a weekday_indexed or weekday_last from this weekday.

Non-members

Name Description
from_stream Parse a weekday from the given stream using the specified format.
operator+ Add specified number of weekdays to this weekday.
operator- Subtract the specified number of weekdays from this weekday, or find the difference between two weekday objects.
operator== Determine whether two weekday objects are equal.
operator<< Output a weekday to a stream.

Requirements

Header: <chrono> Since C++20

Namespace: std::chrono

Compiler Option: /std:c++latest

Constructors

Constructs a weekday.

1) weekday() = default; // C++20
2) explicit constexpr weekday(unsigned wd) noexcept; // C++20
3) constexpr weekday(const sys_days& dp) noexcept; // C++20
4) explicit constexpr weekday(const local_days& dp) noexcept; // C++20

Parameters

dp
Construct a weekday using the day of the week dp.

wd
Construct a weekday with value wd.

Remarks

1) The default constructor doesn't initialize the weekday value.
2) Construct a weekday with the specified value.
If wd is 7, the weekday is constructed with a value of 0.
Don't initialize with values over 255 or the resulting weekday will have an unspecified value.
3) Computes what day of the week corresponds to the std::chrono::sys_days value dp, and constructs a weekday using that day.
4) Computes the day of the week that corresponds to the std::chrono::local_days value dp, and constructs a weekday using that day. It behaves as if you created the weekday using weekday(std::chrono::sys_days(dp.time_since_epoch())).

Example: Create a weekday

// compile using: /std:c++latest
#include <iostream>
#include <chrono>

using namespace std::chrono;

int main()
{
    weekday wd{ Wednesday };
    weekday wd2{ 3 };
    std::cout << wd << '\n' << wd2;
    
    return 0;
}

Wednesday
Wednesday

c_encoding

constexpr unsigned c_encoding() const noexcept;

Return value

The weekday value.

iso_encoding

The weekday value, but with Sunday (0) is interpreted as 7 per ISO 8601.

constexpr unsigned iso_encoding() const noexcept;

Return value

The weekday value.

ok

Check if the value stored in this weekday is in the valid range.

constexpr bool is_leap() const noexcept;

Return value

true if the weekday value is in the range [0, 6]. Otherwise, false.

operator++

Add 1 to the weekday value.

1) constexpr std::chrono::weekday& operator++() noexcept;
2) constexpr std::chrono::weekday operator++(int) noexcept;

Return value

1) A reference to *this weekday after it has been incremented (a postfix increment).
2) A copy of the weekday, before it has been incremented (a prefix increment).

Example: operator++

// compile using: /std:c++latest
#include <iostream>
#include <chrono>

using namespace std;
using namespace std::chrono;

int main()
{
    std::chrono::weekday wd{Thursday};

    std::cout << wd << " " << ++wd << "\n"; // constexpr weekday& operator++() noexcept
    std::cout << wd << " " << wd++ << "\n"; // constexpr weekday operator++(int) noexcept
    std::cout << wd << "\n";

    return 0;
}

Thu Fri
Fri Fri
Sat

Remarks

The incremented value is modulo 7. It will always be in the range [0, 6].

operator--

Subtract 1 from the weekday value.

1) constexpr std::chrono::weekday& operator--() noexcept;
2) constexpr std::chrono::weekday operator--(int) noexcept;

Return value

1) A reference to *this weekday after it has been decremented (a postfix decrement).
2) A copy of the weekday before it has been decremented (a prefix decrement).

Example: operator--

// compile using: /std:c++latest
#include <iostream>
#include <chrono>

using namespace std;
using namespace std::chrono;

int main()
{
    weekday y = weekday{Thursday};

    cout << y << " " << --y << "\n"; // constexpr weekday& operator--() noexcept
    cout << y << " " << y-- << "\n"; // constexpr weekday operator--(int) noexcept
    cout << y << "\n";

    return 0;
}

Thu Wed
Wed Wed
Tue

Remarks

If the decremented result is less than 0, it's set to 6.

operator+=

Add days to a weekday.

constexpr weekday& operator+=(const days& d) noexcept;

Parameters

*d*
The number of days to add.

Return value

The value of *this + d. The result will be modulo 7, in the range [0, 6].

operator-=

Subtract days from the weekday.

constexpr weekday& operator-=(const days& d) noexcept;

Parameters

*d*
The number of days to subtract.

Return value

The value of *this - d. The result will be modulo 7, in the range [0, 6].

operator[]

Create a weekday_indexed or weekday_last from this weekday.

1) std::chrono::weekday_indexed(*this, index) // C++20
2) std::chrono::weekday_last(*this) // C++20

Return value

1) std::chrono::weekday_indexed(*this, index)
2) std::chrono::weekday_last(*this)

Example: operator[]

// compile using: /std:c++latest
#include <iostream>
#include <chrono>

using namespace std;
using namespace std::chrono;

int main()
{
    constexpr auto firstMondayInJanuary =
        year_month_day{ Monday[2] / January / 2021y };

    std::cout << firstMondayInJanuary << "\n";

    constexpr auto lastMondayInJanuary = 
        year_month_day{ Tuesday[last] / January / 2021y };
    std::cout << lastMondayInJanuary << "\n";
}

2021-01-11
2021-01-26

Weekday constants

(C++20) The <chrono> header defines the following constants that you can use with weekday for greater convenience, type-safety, and maintainability of your code. These constants are in scope when std::chrono is in scope.

// Calendrical constants
inline constexpr std::chrono::weekday Sunday{0};
inline constexpr std::chrono::weekday Monday{1};
inline constexpr std::chrono::weekday Tuesday{2};
inline constexpr std::chrono::weekday Wednesday{3};
inline constexpr std::chrono::weekday Thursday{4};
inline constexpr std::chrono::weekday Friday{5};
inline constexpr std::chrono::weekday Saturday{6};

See also

weekday_last class
weekday_indexed class
<chrono>
Header Files Reference