PHPにおける日付時刻の処理大全 - Qiita

<?php $year = 2020; $month = 10; $day = 30; //$res = convertToJapaneseDate($year, $month, $day) ?? '不正な日時です'; $res = convertToJapaneseDate($year, $month, $day) ?: '不正な日時です'; echo $res; //明治6年より前は返さない //function convertToJapaneseDate(int $year, int $month, int $day): ?string function convertToJapaneseDate(int $year, int $month, int $day): string { $REIWA = 20190501; $HEISEI = 19890108; $SHOWA = 192