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month class

  • Artikkeli

Represents a month of a year. For example, July.

Syntax

class month; // C++20

Remarks

A month normally holds values in the range [1, 12]. It can also hold non-negative values outside this range. See Month constants, below, for constants that you can use with the month class.

Members

Name Description
Constructors Construct a month.
ok Verify that the month value is in the valid range [1,12].
operator++ Increment the month.
operator+= Add the specified number of months to this month.
operator-- Decrement this month.
operator-= Subtract the specified number of months from this month.
operator unsigned Get the month value.

Non-members

Name Description
from_stream Parse a month from the given stream using the specified format.
operator+ Add specified number of months to this month, returning a new month instance.
operator- Subtract the specified number of months from this month. Returns a new month instance.
operator== Determine whether two months are equal.
operator<=> Compare this month against another month. The >, >=, <=, <, != operators are synthesized by the compiler.
operator<< Output a month to the given stream.

Requirements

Header: <chrono> (since C++20)

Namespace: std::chrono

Compiler Option: /std:c++latest

Constructors

Construct a month.

1) month() = default;
2) explicit constexpr month(unsigned m) noexcept;

Parameters

m
Construct a month with value m.

Remarks

1) The default constructor doesn't initialize the day value.
2) Construct a month with the day value initialized to m.

ok

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

constexpr bool ok() const noexcept;

Return value

true if the month value is in the range [1,12]. Otherwise, false.

operator++

Increment the month value.

1) constexpr month& operator++() noexcept;
2) constexpr month operator++(int) noexcept;

Return value

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

Example: operator++

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

using namespace std::chrono;

int main()
{
    month m{ January };
    month m2{4}; // April

    std::cout << m << " " << ++m << "\n"; // constexpr month& operator++() noexcept
    std::cout << m << " " << m++ << "\n"; // constexpr month operator++(int) noexcept
    std::cout << m << "\n";
    std::cout << m2 << "\n";

    return 0;
}

Jan Feb
Feb Feb
Mar
Apr

Remarks

If the result exceeds 12, it's set to 1.

operator--

Subtract 1 from the month value.

1) constexpr month& operator--() noexcept;
2) constexpr month operator--(int) noexcept;

Return value

1) A reference to *this month after it has been decremented (a postfix decrement).
2) A copy of the month 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()
{
    month m{May};

    cout << m << " " << --m << "\n"; // constexpr month& operator++() noexcept
    cout << m << " " << m-- << "\n"; // constexpr month operator++(int) noexcept
    cout << m << "\n";

    return 0;
}

May Apr
Apr Apr
Mar

Remarks

If the decremented result is less than 1, it's set to 12.

operator+=

Add months to this month.

constexpr month& operator+=(const months& m) noexcept;

Parameters

m
The number of months to add.

Return value

*this

operator-=

Subtract months from this month.

constexpr month& operator-=(const months& m) noexcept;

Parameters

m
The months to subtract.

Return value

*this.

operator unsigned

Get the unsigned month value.

explicit constexpr operator unsigned() const noexcept;

Return value

The unsigned value of this month

Example: operator unsigned()

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

using namespace std::chrono;

int main()
{
    month m{July};
    unsigned monthValue = static_cast<unsigned>(m);
    std::cout << monthValue << "\n";

    return 0;
}

7

Month constants

(C++20) The <chrono> header defines the following constants that you can use with month 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 month January{1};
inline constexpr month February{2};
inline constexpr month March{3};
inline constexpr month April{4};
inline constexpr month May{5};
inline constexpr month June{6};
inline constexpr month July{7};
inline constexpr month August{8};
inline constexpr month September{9};
inline constexpr month October{10};
inline constexpr month November{11};
inline constexpr month December{12};

See also

<chrono>
month_day Class
month_day_last Class
month_weekday Class
month_weekday_last class