PHP7引入的＂??＂和＂?:＂的区别讲解

<?php  $array = [    'a' => 1,    'b' => 2,    'c' => [],  ];  $a = $array['c'] ?? 0;  $b = $array['c'] ?: 0;  $c = $array['d'] ?? 0;  $d = $array['d'] ?: 0;  $e = $array['c'] ? 1 : 0;  $f = isset($array['c']) ? 1 : 0;  $g = $array['d'] ? 1 : 0;  $h = isset($array['d']['e']) ? 1 : 0;  $i = !empty($array['c']) ? 1 : 0;  $j = !empty($array['d']) ? 1 : 0;  var_dump($a);  var_dump($b);  var_dump($c);  var_dump($d);  var_dump($e);  var_dump($f);  var_dump($g);  var_dump($h);  var_dump($i);  var_dump($j);