php array query key

In PHP, array is one of the most commonly used data structures. It can store multiple elements, which can be various types of data, such as strings, integers, floating point numbers, Boolean values, objects, etc. Due to their flexibility and efficiency, arrays have become an essential component in developing web applications.

In an array, each element consists of a key and a value. A key is a unique identifier for an element in an array and is used to access the element's value. In PHP, there are two ways to create arrays: associative arrays and indexed arrays.

Associative array refers to an array corresponding to key values, and each element has a unique key. Indexed arrays locate elements by numerical index. In this article, we mainly introduce the key query of associative arrays.

Querying the keys of an associative array usually uses two array functions: array-key-exists() and array-keys().

array-key-exists() function is used to check whether an array contains the specified key. The syntax is as follows:

bool array_key_exists (mixed $key, array $array)

Among them, $key represents the array key value that needs to be found, and $array represents the array that needs to be queried. Returns true if the specified key is found in the array, false otherwise.

For example, we have an associative array $array, which contains multiple key-value pairs:

$array = [
    "name" => "John",
    "age" => 25,
    "gender" => "male"
];

We can use the array_key_exists() function to query whether there is a named "name" in $array " key:

if (array_key_exists("name", $array)) {
    echo "The key 'name' exists in the array.";
} else {
    echo "The key 'name' does not exist in the array.";
}

This will output:

The key 'name' exists in the array.

If we change the key name, query the array using a non-existent key:

if (array_key_exists("email", $array)) {
    echo "The key 'email' exists in the array.";
} else {
    echo "The key 'email' does not exist in the array.";
}

This will output:

The key 'email' does not exist in the array.

When we need to query all the keys in an array, we can use the array-keys() function.

array-keys() function is used to return an array of all keys in the array. The syntax is as follows:

array array_keys (array $array [, mixed $search_value = null [, bool $strict = false ]] )

Among them, $array is the array to be queried, $ search_value is an optional parameter, which indicates the key value that needs to be searched in the array, and $strict indicates whether to perform strict type comparison.

For example, we have an associative array $array, which contains multiple key-value pairs:

$array = [
    "name" => "John",
    "age" => 25,
    "gender" => "male"
];

We can use the array_keys() function to query all keys in the array:

$keys = array_keys($array);
print_r($keys);

This will output:

Array (
    [0] => name
    [1] => age
    [2] => gender
)

If we query for a specific key value in the array:

$keys = array_keys($array, "John");
print_r($keys);

This will output:

Array (
    [0] => name
)

When using the array-keys() function When , we can also use the third parameter $strict to control whether strict type comparison is performed. For example, we change the key name "age" to an integer type:

$array = [
    "name" => "John",
    25 => "male"
];

If we query using the default non-strict type:

$keys = array_keys($array, "male");
print_r($keys);

this will output:

Array (
    [0] => name
    [1] => 25
)

When we use strict type query:

$keys = array_keys($array, "male", true);
print_r($keys);

This will output:

Array (
    [0] => 25
)

In summary, PHP provides a wealth of array operation functions that can help us operate arrays quickly and easily. In daily use, we should flexibly use these functions according to actual needs to improve the efficiency of array query, addition, deletion and other operations.

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