将字符串传递给sprintf语法

Question

我只是想把日期作为DATE（XXXX-XX-XX格式）传递给sql，但我似乎无法让sprintf接受我的字符串日期组件。我似乎正确地遵循文档。使用php5.5

$year = ($_POST['year']);
$month = ($_POST['month']); 
$day = ($_POST['day']);

var_dump显示：

 string(4) "1991" string(1) "8" string(1) "5"

然而这两个var_dump都是空的：

$dobexpanded =sprintf("%04s-%02s-%02s", $year, $month, $day);
$dateofbirth = (STR_TO_DATE('$dobexpanded', '%Y-%m-%d'));
var_dump($dobexpanded);
var_dump($dateofbirth);

Answer 1

试试这个：

date('Y-m-d', mktime(0, 0, 0, $month, $day, $year));

Answer 2

尝试 -

$dobexpanded =sprintf("%04d-%02d-%02d", $year, $month, $day);
$dateofbirth = date('Y-m-d', strtotime($dobexpanded));
var_dump($dobexpanded);
var_dump($dateofbirth);