主要区别是两个或者多个数组中如果出现相同键名，键名分为字符串或者数字，需要注意
1）键名为数字时，array_merge()不会覆盖掉原来的值，但＋合并数组则会把最先出现的值作为最终结果返回，而把后面的数组拥有相同键名的那些值“抛弃”掉（不是覆盖）
2）键名为字符时，＋仍然把最先出现的值作为最终结果返回，而把后面的数组拥有相同键名的那些值“抛弃”掉，但array_merge()此时会覆盖掉前面相同键名的值
需要注意的是数组键形式 ‘数字‘ 等价于 数字
$a = array(‘a‘,‘b‘);
$b = array(‘c‘, ‘d‘);
$c = $a + $b;
var_dump($a);
var_dump(array_merge($a, $b));
$a = array(0 => ‘a‘, 1 => ‘b‘);
$b = array(0 => ‘c‘, 1 => ‘b‘);
$c = $a + $b;
var_dump($c);
var_dump(array_merge($a, $b));
$a = array(‘a‘, ‘b‘);
$b = array(‘0‘ => ‘c‘, 1 => ‘b‘);
$c = $a + $b;
var_dump($c);
var_dump(array_merge($a, $b));
$a = array(0 => ‘a‘, 1 => ‘b‘);
$b = array(‘0‘ => ‘c‘, ‘1‘ => ‘b‘);
$c = $a + $b;
var_dump($c);
var_dump(array_merge($a, $b));
结果
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
=> string ‘c‘ (length=1)
=> string ‘d‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
=> string ‘c‘ (length=1)
=> string ‘b‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
=> string ‘c‘ (length=1)
=> string ‘b‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
array
=> string ‘a‘ (length=1)
=> string ‘b‘ (length=1)
=> string ‘c‘ (length=1)
=> string ‘b‘ (length=1)