PHP理解用于提取复选框值的小片段代码

Question

I have a snippet of PHP code, it works but I was curious to know why.

Green: <input type="checkbox" name="color[]" value="green" />
Black: <input type="checkbox" name="color[]" value="black" />
White: <input type="checkbox" name="color[]" value="white" />
Blue:  <input type="checkbox" name="color[]" value="blue"  />
Red:   <input type="checkbox" name="color[]" value="red"   />

then here is what I don't get for this PHP code below, how is $colors an array, I thought you have to at least have $colors[] = $_POST['color'].

if (isset($_POST['color'])) {
  $colors = $_POST['color'];
}
echo $colors[0];

Thanks for helping me better understand this.

Answer 1

You don't need to explicitly add [] in PHP. Notice that you don't even need to define the type! This is PHP :)

$_POST['color'] is an array, so $colors will also be!

Read: http://www.html-form-guide.com/php-form/php-form-checkbox.html

Edit

In PHP, if you write $colors[] = $var, you are actually adding $var to the end of that array. If the array is empty, $colors[0] == $var.

$colors = $_POST['color']; // $colors receives the array
$colors[] = $_POST['color']; // $colors[0] receives the array, if $colors was empty

More info: http://php.net/manual/en/language.types.array.php#language.types.array.syntax.modifying