合并两个数组的两种方式的异同

本文讨论合并数组的两种方式：$a+$b , array_merge($a,$b)

操作符+，在前一个数的基础上插入后一个数组，假设有同样的抛弃，而array_merge 是在前一个參数基础上插入后一个參数。假设有同样用的key 用后一个覆盖。实比例如以下：

php > $a = array('a'=>'1','b'=>'2','c'=>'3');
php > $b = array('c'=>3,'d'=>'4','e'=>'5');
php > $c = $a+$b;
php > $d = array_merge($a,$b);
php > var_dump($c,$d);
array(5) {
'a' =>
string(1) "1"
'b' =>
string(1) "2"
'c' =>
string(1) "3"
'd' =>
string(1) "4"
'e' =>
string(1) "5"
}
array(5) {
'a' =>
string(1) "1"
'b' =>
string(1) "2"
'c' =>
int(3)
'd' =>
string(1) "4"
'e' =>
string(1) "5"
}
php > $e = array_merge($b,$a);
php > var_dump($e);
array(5) {
'c' =>
string(1) "3"
'd' =>
string(1) "4"
'e' =>
string(1) "5"
'a' =>
string(1) "1"
'b' =>
string(1) "2"
}
php > $f=$b+$a;
php > var_dump($f);
array(5) {
'c' =>
int(3)
'd' =>
string(1) "4"
'e' =>
string(1) "5"
'a' =>
string(1) "1"
'b' =>
string(1) "2"
}

当两边都是索引数组时。使用array_merge 可能会引起索引重置，如以下这样的情况：

php > $a = array();
php > $b = array(1=>'data');
php > $c = $a+$b;
php > $d = array_merge($a,$b);
php > var_dump($c,$d);
array(1) {
[1] =>
string(4) "data"
}
array(1) {
[0] =>
string(4) "data"

}

所以，当使用+来合并两个索引数组。值可能会被丢弃，而array_merge就不会，会把反复的索引重置：

php > $a = array(1=>'one',2=>'two',3=>'three');
php > $b = array(3=>'three',4=>'four',5=>'five');
php > $c = $a+$b;
php > $d = array_merge($a,$b);
php > var_dump($c,$d);
array(5) {
[1] =>
string(3) "one"
[2] =>
string(3) "two"
[3] =>
string(5) "three"
[4] =>
string(4) "four"
[5] =>
string(4) "five"
}
array(6) {
[0] =>
string(3) "one"
[1] =>
string(3) "two"
[2] =>
string(5) "three"
[3] =>
string(5) "three"
[4] =>
string(4) "four"
[5] =>
string(4) "five"
}