What key names can be used for arrays in php

Arrays in PHP are one of the very important data types that can store multiple data elements and access them as key-value pairs. Arrays can be a very good choice when we need to put a set of data together and use them. In PHP, we can use different key names to access arrays. Below, I'll introduce some commonly used key names and their uses.

1. Numeric key name

Numeric key name is the most common and simplest type of key name, and any integer can be used as the key name of the array. This type of key name is very convenient when looping through an array, because it makes it easy to find a specific element through the loop. For example, here is an array using numeric key names:

$myArray = array(0 => 'apple', 1 => 'orange', 2 => 'banana');

In the above example, we defined an array with three elements. Each element has a numeric key name, they are 0, 1 and 2 respectively. We can use a for loop to traverse the array:

for ($i = 0; $i < count($myArray); $i++) {
    echo $myArray[$i] . "\n";
}

2. String key name

In PHP, in addition to numeric key names, we can also use string keys name. This type of key name can be any string, including letters, numbers, and special characters. If the key name in the array is a string, the array element can be accessed through the key name. For example:

$myArray = array("name" => "Tom", "age" => 18, "gender" => "male");

In the above example, we defined an array containing three elements. All key names are strings, they are "name", "age" and "gender". We can access array elements through these key names:

echo $myArray["name"] . "\n";  // 输出：Tom
echo $myArray["age"] . "\n";   // 输出：18
echo $myArray["gender"] . "\n";  // 输出：male

3. Boolean key name

In addition to numeric and string key names, PHP also supports Boolean key names . Key names of this type can only be true or false. If the key in the array is true, its value will overwrite the value of the element with the key false. For example:

$myArray = array(false => 'apple', true => 'orange', false => 'banana');

In the above example, we defined an array containing three elements. Among them, the key names of the first and third elements are false, and the key name of the second element is true. Since the element with the key name true is assigned at the end, its value is "orange". If we use the following code to print an array:

print_r($myArray);

The output result is:

Array
(
    [0] => banana
    [1] => orange
)

It can be seen that Boolean key names are not common and can easily cause confusion, so they should be used with caution.

4. Null value/NULL key name

In PHP, you can use null value/NULL as the key name of the array. However, this type of key names is less common because they are significantly different from key names of other data types. For example, here is an array with NULL key names:

$myArray = array(NULL => 'apple', 'orange' => 5, false => 'banana');

In the above example, we defined an array with three elements. Among them, the key name of the first element is NULL, the key name of the second element is "orange", and the key name of the third element is false. If we iterate over the array and use var_dump() to print the value and type of each element:

foreach ($myArray as $key => $value) {
    var_dump($key, $value);
}

The output result is:

NULL
string(5) "apple"
string(6) "orange"
int(5)
bool(false)
string(6) "banana"

It can be seen that the empty value/NULL key name Although legal, they often have no practical application.

To sum up, arrays in PHP support multiple types of key names, and you can choose the appropriate key name type according to actual needs. Numeric and string key names are the most commonly used types, while Boolean and null/NULL key names are less commonly used. No matter which type of key name you use, you need to pay attention to the uniqueness of the key name to avoid unexpected errors.

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