What are the subscript requirements for arrays in php

In PHP, array is one of the important data types, which is very suitable for storing a set of ordered data. Each element in the array has a corresponding key value or subscript. Array subscripts in PHP have some requirements. This article will introduce them to you in detail.

1. The array subscript must be an integer or string type

The array subscript in PHP must be an integer or string type. Among them, the integer type subscript can be any legal integer, including negative numbers and 0; the string type subscript can be any legal string, including numbers and letters, etc.

For example:

$arr1 = array(1, 2, 3);
$arr2 = array("name" => "张三", "age" => 18);

In the $arr1 array, the subscripts 0, 1, and 2 are all integer types; in the $arr2 array, the subscripts are "name". and "age", both of string type.

2. The array subscript cannot be a floating point number

The array subscript in PHP cannot be a floating point number type, even a double precision floating point number (double) is not allowed . This is because when using floating point numbers as subscripts, there may be precision errors that prevent the subscripts from matching correctly.

For example:

$arr = array(1.3 => "张三", 2.6 => "李四");

The $arr array defined by the above code will throw an error message "Warning: Illegal offset type" because the subscript is a floating point type.

3. Array subscripts must be unique

Array subscripts in PHP must be unique. If there are duplicate subscripts, subsequent elements will overwrite previous elements. , called the "covering effect".

For example:

$arr = array(1, 2, 3, 3);
print_r($arr);

In the $arr array defined by the above code, the element with subscript 3 appears twice, and the subsequent element value is 3, so the output result is: Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 3 ), with the fourth element covering the third element.

However, it should be noted that if the subscripts of different types are equal, they will be regarded as equal subscripts, for example:

$arr = array("1" => "张三", 1 => "李四");
print_r($arr);

The $arr array defined in the above code, due to the subscript "1" and 1 are regarded as equal subscripts, so the output result is: Array ([1] => Li Si), that is, the later elements cover the previous elements.

4. Array subscripts can be omitted

If the subscript is not explicitly specified when defining the array, PHP will automatically assign an integer type subscript to each element. The starting value is 0, and the index of each element is incremented by 1.

For example:

$arr = array("张三", "李四", "王五");
print_r($arr);

In the $arr array defined in the above code, there is no explicit subscript specified, so PHP will automatically assign integer type subscripts 0, 1, and 2, and output The result is: Array ([0] => Zhang San[1] => Li Si[2] => Wang Wu).

5. The array subscript can be a variable

In PHP, the array subscript can be a variable, that is, the array subscript can be dynamically specified through a variable. This can dynamically modify array elements while the program is running, which is very flexible.

For example:

$id = "uid";
$arr = array($id => 1001, "name" => "张三");
echo $arr[$id]; // 输出结果为：1001

In the above code, the value of the variable $id is "uid", which is one of the subscripts of the $arr array, realizing dynamically specifying the array subscript through the variable. Function.

Summary:

Array is one of the very important data types in PHP, used to store a set of ordered data. The array subscript is the identifier of each element in the array and must meet the following requirements: it must be an integer or string type, it cannot be a floating point number type, it must be unique, it can be omitted, and it can be a variable. Reasonable use of array subscripts can allow us to better utilize PHP's array functions and improve programming efficiency.

The above is the detailed content of What are the subscript requirements for arrays in php. For more information, please follow other related articles on the PHP Chinese website!