How to query array return keys using PHP

PHP is a widely used server-side programming language. During the development process, it is often necessary to use arrays to store and manipulate data. Array is an efficient data structure that can store large amounts of data and facilitate query, modification, addition, and deletion operations. In this article, we will explain how to use PHP to query an array to return keys.

In PHP, arrays can be defined in the following two ways:

1. Use the array() function to define, the syntax is as follows:

   $array = array(value1, value2, value3, ......);

2. Directly use square brackets [] to define, the syntax is as follows:

   $array = [value1, value2, value3, ......];

Note that all key names in the PHP array are string types, if not explicitly defined The key name starts from 0 and increases by default.

There are many ways to use PHP to query arrays to return keys, including key names and key values. Below we will introduce these two methods respectively.

1. Query the key name of the array

In PHP, you can use the array_keys() function to query the key name of the array. The syntax of this function is as follows:

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

This function accepts three parameters:

• $input: required, the array to be queried.
• $search_value: Optional, the key value to be searched.
• $strict: Optional, whether to use strict mode, the default is false.

The return value of this function is a new array containing all key names. The key names of the returned array are the key names in the original array, and the key values ​​are the key values ​​in the original array.

The following is an example of querying the key name of an array:

<?php //定义数组
$array = ["name" => "Tom", "age" => 20, "location" => "Shanghai"];

//查询数组键名
$keys = array_keys($array);

//输出查询结果
print_r($keys);
?>

The output result is:

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

In the above code, we use the array_keys() function to query the array $array Key name, store the query results in the $keys variable, and use the print_r() function to output the query results to the page.

2. Query the key value of the array

In PHP, you can use the array_search() function to query the key value of the array. The syntax of this function is as follows:

mixed array_search(mixed $needle, array $haystack [, bool $strict = false ])

This function accepts three parameters:

• $needle: required, the key value to be queried.
• $haystack: required, the array to be queried.
• $strict: Optional, whether to use strict mode, the default is false.

The return value of this function is the key name containing the key value. If it is not found, it returns false.

The following is an example of querying the key value of an array:

<?php //定义数组
$array = ["name" => "Tom", "age" => 20, "location" => "Shanghai"];

//查询数组键值
$index = array_search("Shanghai", $array);

//输出查询结果
echo $index;
?>

The output result is:

location

In the above code, we use the array_search() function to query the array $array The key value is the key name of "Shanghai", and the query results are stored in the $index variable, and the echo() function is used to output the query results to the page.

Summary

This article introduces how to use PHP to query arrays to return keys, mainly including two methods: querying array key names and querying array key values. Using these methods, you can easily manipulate and query arrays, thereby developing PHP applications more efficiently. Hope this helps.

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