+ operator for array in PHP?

Carefull with numeric keys, if they should be preserved or if you don't want to loose anything

$a = array(2 => "a2", 4 => "a4", 5 => "a5");
$b = array(1 => "b1", 3 => "b3", 4 => "b4");

union

print_r($a+$b);
Array
(
    [2] => a2
    [4] => a4
    [5] => a5
    [1] => b1
    [3] => b3
)

merge

print_r(array_merge($a, $b));
Array
(
    [0] => a2
    [1] => a4
    [2] => a5
    [3] => b1
    [4] => b3
    [5] => b4
)

$var1 = "example";
$var2 = "test";
$output = array_merge((array)$var1,(array)$var2);
print_r($output);

Array ( [0] => example [1] => test )

The best example I found for using this is in a config array.

$user_vars = array("username"=>"John Doe");
$default_vars = array("username"=>"Unknown", "email"=>"[email protected]");

$config = $user_vars + $default_vars;

The $default_vars, as it suggests, is the array for default values. The $user_vars array will overwrite the values defined in $default_vars. Any missing values in $user_vars are now the defaults vars from $default_vars.

This would print_r as:

Array(2){
    "username" => "John Doe",
    "email" => "[email protected]"
}

I hope this helps!

This operator takes the union of two arrays (same as array_merge, except that with array_merge duplicate keys are overwritten).

The documentation for array operators is found here.

The + operator appends elements of remaining keys from the right handed array to the left handed, whereas duplicated keys are NOT overwritten.

<?php
$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");

$c = $a + $b; // Union of $a and $b
echo "Union of \$a and \$b: \n";
var_dump($c);

$c = $b + $a; // Union of $b and $a
echo "Union of \$b and \$a: \n";
var_dump($c);
?>

When executed, this script will print the following:

Union of $a and $b:
array(3) {
  ["a"]=>
  string(5) "apple"
  ["b"]=>
  string(6) "banana"
  ["c"]=>
  string(6) "cherry"
}
Union of $b and $a:
array(3) {
  ["a"]=>
  string(4) "pear"
  ["b"]=>
  string(10) "strawberry"
  ["c"]=>
  string(6) "cherry"
}

not exactly like array_merge

Note that the plus operator for arrays ‘+’ is only one-dimensional, and is only suitable for simple arrays.

read more :

http://www.vancelucas.com/blog/php-array_merge-preserving-numeric-keys/

It will append the new array to the previous.