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
复制代码 代码如下:
$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
复制代码 代码如下:
array
0 => string "a" (length=1)
1 => string "b" (length=1)
2 => string "c" (length=1)
3 => string "d" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)
2 => string "c" (length=1)
3 => string "b" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)
2 => string "c" (length=1)
3 => string "b" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)

array
0 => string "a" (length=1)
1 => string "b" (length=1)
2 => string "c" (length=1)
3 => string "b" (length=1)