Definition and Destruction of PHP Arrays_PHP Tutorial

The most commonly used way to define data in php is array(). Of course, if you don’t know the length of the array, you can define the unknown data length like array[]. If you want to clear the data, we can directly unset(array [key]) or directly return empty value.

Data definition

The code is as follows

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代码如下	复制代码
…… $array = array('one','two','three'); var_dump($array); ……

……

$array = array('one','two','three');

var_dump($array);

代码如下	复制代码
array(3) { [0]=> string(3) "one" [1]=> string(3) "two" [2]=> string(5) "three" }

……

In the first line of this code snippet, a one-dimensional array $array is defined. In the second line, we format and output the array. The result is like this:

The code is as follows

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array(3) { [0]=>

代码如下	复制代码
…… $array = array('one',”hello”=>'two','three'); var_dump($array);

string(3) "one"

[1]=>

string(3) "two"

代码如下	复制代码
array(3) { [0]=> string(3) "one" ["hello"]=> string(3) "two" [1]=> string(5) "three" }

[2]=>

string(5) "three"

}

Now brothers explain this output result. First, the first line of the output result of this array,

代码如下	复制代码
…… $array = array(-5=>'one',"hello"=>'two','three'); var_dump($array); ……

array(3) tells us that this is an array with three elements, First, element 0 is a string of length 3 (string(3))... Due to space constraints, I won’t talk about the remaining two. Hoho…, what does this mean? This shows that in PHP, if we do not specify a subscript for the array, then it will make a subscript for us from scratch on its own initiative - that is, the key name in the PHP array; look at the following example:

The code is as follows	Copy code
…… $array = array('one',"hello"=>'two','three'); var_dump($array);

...This time when we defined the array, we specified a subscript for the second element (from now on, it will be called a key name in this article, the subscript is a bit ambiguous!), and the second element specified Key name (hello), let’s take a look at the output:

The code is as follows	Copy code
array(3) { [0]=> string(3) "one" ["hello"]=> string(3) "two" [1]=> string(5) "three" }

I think you have also seen a very smart phenomenon like me. The key name of the first element is still 0 - we can understand this because we did not specify it, and the PHP array must have a key name, PHP We created a key name from scratch on our own initiative; for the second element, we specified the key name, and PHP respected our opinion and used this key name; the complicated thing is in the third element, The third element looks very simple. We did not specify a key name. PHP automatically adds 1 to the maximum integer key name as the key name. But have you ever thought about it, if we change the key name of the first element to "-5" and the key name of the second element remains unchanged, what will be the result? Let’s wait and see:

The code is as follows	Copy code
…… $array = array(-5=>'one',"hello"=>'two','three'); var_dump($array); ……

If you take it for granted that the key name of the third element should be -4, then I tell you that this idea was correct before PHP4.3.0, but it was wrong after that, and now it is after PHP4.3.0 Version you will see the following results:

string(3) "two" [0]=>

The code is as follows

代码如下	复制代码
array(3) { [-5]=> string(3) "one" ["hello"]=> string(3) "two" [0]=> string(5) "three" }

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array(3) {
[-5]=>
string(3) "one"

["hello"]=>

string(5) "three" }

Yes, the third element starts from 0, that is, no matter how small your negative number is, if the next element is asked to define the key name by PHP, then it will start from 0 - remember this place says What's interesting is that if the largest key name among the existing keys is still a negative number, no matter how small the negative number is, PHP will start the next key name from zero. Destruction of PHP arrays is as simple as destroying other variables. Destroy the entire array: unset($array) Destroy an element in the array: unset($array[-5])

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www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/628975.htmlTechArticleThe most commonly used way to define data in php is array(). Of course, if you don’t know the length of the array You can define the unknown data length like array[]. If you want to clear the data, we...