std::chrono...rono::make24(3)

💖 NAME 💖

okay bestie, welcome to std::chrono...rono::make24(3) from the C++ Standard Libary manual — yes, the header spells it Libary, and we're keeping the lore. 💅 This is the C++ chrono page for the four time-format besties, and it's all since C++20.

std::chrono::is_am,std::chrono::is_pm,std::chrono::make12,std::chrono::make24 — that's the exact NAME-line squad, no cap. 🫶

✨ Synopsis ✨

Defined in header <chrono>.

• (1) (since C++20) — constexpr bool is_am( const std::chrono::hours& h ) noexcept;
• (2) (since C++20) — constexpr bool is_pm( const std::chrono::hours& h ) noexcept;
• (3) (since C++20) — constexpr std::chrono::hours make12( const std::chrono::hours& h ) noexcept;
• (4) (since C++20) — constexpr std::chrono::hours make24( const std::chrono::hours& h, bool is_pm ) noexcept;

These functions aid in translating between a 12-hour format time of day and a 24-hour format time of day. Literally clock math, but make it cute. 🕰️✨

1. Detects whether the 24-hour format time is a.m. (ante meridiem, before midday).
2. Detects whether the 24-hour format time is p.m. (post meridiem, after midday).
3. Returns the 12-hour equivalent of a 24-hour format time.
4. Returns the 24-hour equivalent of a 12-hour format time h, where is_pm determines whether the time is p.m.

🎀 Parameters 🎀

• h — 12-hour or 24-hour format time to detect.
• is_pm — whether the 12-hour format time is p.m.

🌸 Return value 🌸

1. 0h <= h && h <= 11h
2. 12h <= h && h <= 23h
3. If h is in range [0h, 23h], returns the 12-hour equivalent in range [1h, 12h]. Otherwise, the return value is unspecified.
4. If h is in range [1h, 12h], returns the 24-hour equivalent in range [0h, 11h] if is_pm is false, or in range [12h, 23h] otherwise. Otherwise, the return value is unspecified.

🚨 out-of-range h gives an unspecified return value in (3) and (4) — that's the manual's words, bestie, so don't roll those dice. 💀

🦋 Example 🦋

// Run this code

#include <chrono>
#include <iomanip>
#include <iostream>
#include <utility>

int main()
{
    using namespace std::chrono;

    static_assert(
        is_am(10h) &&  is_am(11h) && !is_am(12h) && !is_am(23h) &&
       !is_pm(10h) && !is_pm(11h) &&  is_pm(12h) &&  is_pm(23h)
    );

    std::cout << "make12():\n";

    for (const hours hh : {0h, 1h, 11h, 12h, 13h, 23h})
    {
        const hours am{make12(hh)};
        std::cout << std::setw(2) << hh.count() << "h == "
                  << std::setw(2) << am.count() << (is_am(hh) ? "h a.m.\n" : "h p.m.\n");
    }

    std::cout << "\nmake24():\n";

    using p = std::pair<hours, bool>;

    for (const auto& [hh, pm] : {p{1h, 0}, p{12h, 0}, p{1h, 1}, p{12h, 1}})
    {
        std::cout << std::setw(2) << hh.count()
                  << (pm ? "h p.m." : "h a.m.")
                  << " == " << std::setw(2)
                  << make24(hh, pm).count() << "h\n";
    }
}

Output:

make12():
 0h == 12h a.m.
 1h ==  1h a.m.
11h == 11h a.m.
12h == 12h p.m.
13h ==  1h p.m.
23h == 11h p.m.

make24():
 1h a.m. ==  1h
12h a.m. ==  0h
 1h p.m. == 13h
12h p.m. == 12h

xoxo, your Unix bestie — source/version http://cppreference.com, dated 2024.06.10. 💖