array+array 和 array_merge(array, array)的区别

1、针对索引数组：
$a = array(0 => 'q', 1 => 'w', 2 => 'e');
$b = array(0 => 'a', 4 => 's');

$c = $a + $b;

print_r($c);
//Array
(
[0] => q
[1] => w
[2] => e
[4] => s
)

$d = array_merge($a, $b);
print_r($d);
Array
(
[0] => q
[1] => w
[2] => e
[3] => a
[4] => s
)