how to convert date format in php from dd-mm-yyyy to yyyy-mm-dd code example

Example 1: php date format dd/mm/yyyy

date("d/m/Y", strtotime($str));

Example 2: yyyymmdd to yyyy-mm-dd php

<?php
// both lines output 813470400
echo strtotime("19951012"), "\n",
     strtotime("12 October 1995");

// prints 1995 Oct 12
echo date("Y-m-d", strtotime("19951012"));
?>