对数组的array_merge函数和+运算符比较迷惑，用以下程序检测下二者的不同。
特别是+运算符，将右边的数组单元（去重复）追加到左边数组的后面。
例子：
<?php
echo "rn第一种情况rn";
$a=array(1,2,3,4,5,6);
$b=array(7,8,9);
$c=array_merge ($a,$b);
print_r($c);
$c=$a+$b;
print_r($c);
$c=$b+$a;
print_r($c);
echo "rn第二种情况rn";
$a=array('a','b','c','d','e','f');
$b=array('a','x','y');
$c=array_merge ($a,$b);
print_r($c);
$c=$a+$b;
print_r($c);
$c=$b+$a;
print_r($c);
echo "rn第三种情况rn";
$a=array(
1=>'a',
2=>'b',
3=>'c',
4=>'d',
5=>'e',
6=>'f');
$b=array(
1=>'a',
7=>'x',
8=>'y');
$c=array_merge ($a,$b);
print_r($c);
$c=$a+$b;
print_r($c);
$c=$b+$a;
print_r($c);
?>
输出结果：
第一种情况
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
[6] => 7
[7] => 8
[8] => 9
)
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 5
[5] => 6
)
Array
(
[0] => 7
[1] => 8
[2] => 9
[3] => 4
[4] => 5
[5] => 6
)
第二种情况
Array
(
[0] => a
[1] => b
[2] => c
[3] => d
[4] => e
[5] => f
[6] => a
[7] => x
[8] => y
)
Array
(
[0] => a
[1] => b
[2] => c
[3] => d
[4] => e
[5] => f
)
Array
(
[0] => a
[1] => x
[2] => y
[3] => d
[4] => e
[5] => f
)
第三种情况
Array
(
[0] => a
[1] => b
[2] => c
[3] => d
[4] => e
[5] => f
[6] => a
[7] => x
[8] => y
)
Array
(
[1] => a
[2] => b
[3] => c
[4] => d
[5] => e
[6] => f
[7] => x
[8] => y
)
Array
(
[1] => a
[7] => x
[8] => y
[2] => b
[3] => c
[4] => d
[5] => e
[6] => f
)