NAME

std::chrono::is_am,std::chrono::is_pm,std::chrono::make12,std::chrono::make24 - std::chrono::is_am,std::chrono::is_pm,std::chrono::make12,std::chrono::make24

Synopsis

Defined in header <chrono>
constexpr bool is_am( const std::chrono::hours& h ) noexcept; (1) (since C++20)
constexpr bool is_pm( const std::chrono::hours& h ) noexcept; (2) (since C++20)
constexpr std::chrono::hours make12( const std::chrono::hours& h ) (3) (since C++20)
noexcept;
constexpr std::chrono::hours make24( const std::chrono::hours& h, (4) (since C++20)
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.

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.

Example

// Run this code

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

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