PHP array Definition and destruction _php tutorial

Defining the data in PHP is the most commonly used array () to achieve, of course, if you do not know the length of the array can be like array[] to define the unknown length of the data, if you want to clear the data we can directly unset (Array[key]) or directly complex value NULL.

Data definition

The code is as follows	Copy Code
...... $array = Array (' One ', ' one ', ' one ', ' three '); Var_dump ($array); ......

In the first line of this code fragment, we define a one-dimensional array $array, and in the second row we format the output of this array, and the result is this:

The code is as follows	Copy Code
Array (3) { [0]=> String (3) "One" [1]=> String (3) "both" [2]=> String (5) "three" }

Now the brother explains this output, first the first line of the output of this array,
Array (3) tells us that this is an array of three elements,
First, the No. 0 element is a string with a length of 3 (String (3)) ...
The length of the relationship is two left to say, roar ... what does this mean? This means that in PHP if we do not specify the subscript for the array, then he will be his own self-initiated from scratch to get us a subscript-that is, the key name in the PHP array; and then look at the following example:

The code is as follows	Copy Code
...... $array = Array (' One ', "hello" = = ' ", ' three '); Var_dump ($array);

...... This time when we define the array, we specify the subscript for the second element (since then, it is called the key name in this article, the subscript is a bit vague!). ), the second element specifies the key name (hello), let's look at the output:

The code is as follows	Copy Code
Array (3) { [0]=> String (3) "One" ["Hello"]=> String (3) "both" [1]=> String (5) "three" }

I think you also like me to see a very intelligent phenomenon, the first element of the key name or 0--this we can understand, because we do not specify, and the PHP array must have a key name, PHP has to start from scratch to create a key name, the second element when we specify the key name, PHP uses this key name in respect of our opinions; complex things in the third element,

The third element, which looks very simple, we do not specify the key name, PHP automatically put the maximum integer key name plus 1, as the key name. But have you thought about it, if we change the key name of the first element to "-5", the second element has the same key name, what will the result be? We wait and see:

The code is as follows	Copy Code
...... $array = Array ( -5=> ' one ', "hello" = = ' ", ' three '); Var_dump ($array); ......

If you take it for granted that the third element's key name should be-4, then I'll tell you that the idea was right before PHP4.3.0, but then it was wrong, and now that's the version after PHP4.3.0, you'll see the following result:

The code is as follows	Copy Code
Array (3) { [-5]=> String (3) "One" ["Hello"]=> String (3) "both" [0]=> String (5) "three" }

Yes, the third element is starting from 0, that is, no matter how small your negative number, the next element if you let PHP to define the key name, then he is starting from 0-remember this place is that in the existing key name if the largest is still a negative number, no matter how small negative numbers, PHP also from zero to start the next key name.

The destruction of the PHP array is simple, like destroying other variables.
Destroy entire array: unset ($array)
Destroys an element in an array: unset ($array [-5])

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