DateInterval을 사용한 날짜 연산

DateInterval 개요

DateInterval 생성

<?php
// P = period, T = time separator
$oneYear  = new DateInterval('P1Y');    // 1 year
$sixMonths = new DateInterval('P6M');   // 6 months
$tenDays  = new DateInterval('P10D');   // 10 days
$twoHours = new DateInterval('PT2H');   // 2 hours (T before time)
$complex  = new DateInterval('P1Y2M3DT4H5M6S');

echo $oneYear->y;    // 1
echo $tenDays->d;    // 10

add() 및 sub()

<?php
$dt = new DateTime('2024-01-01');

$dt->add(new DateInterval('P1Y'));   // +1 year
echo $dt->format('Y-m-d');  // 2025-01-01

$dt->sub(new DateInterval('P3M'));   // -3 months
echo $dt->format('Y-m-d');  // 2024-10-01

두 날짜 사이의 diff()

<?php
$start = new DateTime('2024-01-01');
$end   = new DateTime('2024-06-15');

$diff = $start->diff($end);

echo $diff->y;  // years
echo $diff->m;  // months
echo $diff->d;  // days
echo $diff->h;  // hours
echo $diff->days; // total days: 166

사람이 읽기 쉬운 차이

<?php
$birthdate = new DateTime('1990-05-15');
$today     = new DateTime();
$age       = $birthdate->diff($today);

echo $age->y . ' years, ' . $age->m . ' months, ' . $age->d . ' days';

// Check if date is in the past
if ($diff->invert === 1) {
    echo 'Date was in the past';
}

DateInterval::createFromDateString()

<?php
$interval = DateInterval::createFromDateString('1 year 2 months 3 days');

$dt = new DateTime('2024-01-01');
$dt->add($interval);
echo $dt->format('Y-m-d');  // 2025-03-04

// Other examples:
DateInterval::createFromDateString('next monday');
DateInterval::createFromDateString('6 weeks');

DatePeriod — 범위 순회

<?php
$start    = new DateTime('2024-01-01');
$interval = new DateInterval('P1M');  // monthly
$end      = new DateTime('2024-06-01');

$period = new DatePeriod($start, $interval, $end);

foreach ($period as $date) {
    echo $date->format('Y-m') . PHP_EOL;
}
// 2024-01, 2024-02, 2024-03, 2024-04, 2024-05

주간 보고서에 DatePeriod 사용

<?php
$start    = new DateTime('2024-01-01');
$interval = new DateInterval('P7D');  // weekly
$end      = new DateTime('2024-02-01');

$weeks = new DatePeriod($start, $interval, $end);
foreach ($weeks as $week) {
    echo 'Week of: ' . $week->format('Y-m-d') . PHP_EOL;
}

시간 간격 비교

<?php
$a = new DateTime('2024-01-01');
$b = new DateTime('2024-06-01');
$c = new DateTime('2025-01-01');

$diff1 = $a->diff($b)->days;  // 152
$diff2 = $a->diff($c)->days;  // 366

echo ($diff1 < $diff2) ? 'First interval shorter' : 'First interval longer';
// First interval shorter

영업일 계산

<?php
function businessDays(DateTime $from, DateTime $to): int {
    $count = 0;
    $cur   = clone $from;
    while ($cur < $to) {
        $dow = (int) $cur->format('N'); // 1=Mon ... 7=Sun
        if ($dow < 6) $count++;
        $cur->modify('+1 day');
    }
    return $count;
}

$from = new DateTime('2024-05-27');
$to   = new DateTime('2024-06-07');
echo businessDays($from, $to) . ' business days';

만료 날짜 패턴

<?php
function expiresAt(string $duration = 'P30D'): string {
    $dt = new DateTimeImmutable();
    return $dt->add(new DateInterval($duration))->format('Y-m-d H:i:s');
}

echo expiresAt('P30D');   // 30-day trial expiry
echo expiresAt('P1Y');    // 1-year subscription expiry
echo expiresAt('PT1H');   // 1-hour token expiry

빠른 확인

복습: DateInterval