php获取每个月的开始和截止时间

//第一个版本（获得2018年3月的起止时间）

$timestamp = strtotime( '2018-3' );
$start_time = date( 'Y-m-1 00:00:00', $timestamp );
$mdays = date( 't', $timestamp );
$end_time = date( 'Y-m-' . $mdays . ' 23:59:59', $timestamp );
echo $start_time;
echo $end_time;

//第二个版本获得2018年12个月的起止时间

$year = '2018';
$yeararr = [];
$month = [];
for ($i=1; $i <=12 ; $i++) { 
	$yeararr[$i] = $year.'-'.$i;
}
foreach ($yeararr as $key => $value) {
	$timestamp = strtotime( $value );
	$start_time = date( 'Y-m-1 00:00:00', $timestamp );
	$mdays = date( 't', $timestamp );
	$end_time = date( 'Y-m-' . $mdays . ' 23:59:59', $timestamp );

	$month[$key]['start_time'] = $start_time;
	$month[$key]['end_time'] = $end_time;

}
print_r($month);

//第三个版本

function month($year){
	$year = $year;
	$yeararr = [];
	$month = [];
	for ($i=1; $i <=12 ; $i++) { 
		$yeararr[$i] = $year.'-'.$i;
	}
	foreach ($yeararr as $key => $value) {
		$timestamp = strtotime( $value );
		$start_time = date( 'Y-m-1 00:00:00', $timestamp );
		$mdays = date( 't', $timestamp );
		$end_time = date( 'Y-m-' . $mdays . ' 23:59:59', $timestamp );

		$month[$key]['start_time'] = $start_time;
		$month[$key]['end_time'] = $end_time;

	}
	return $month;
}

$year = month(2018);
print_r($year);