How to determine if an array has a key in php

PHP is a widely used server-side scripting language capable of processing data and serving dynamic content from a web server. In PHP, arrays are a very common data type that can store multiple data items, and they can be accessed by key or index. In actual programming, it is often necessary to determine whether an array has a specific key. This article will introduce how to implement it in PHP.

1. Use the array_key_exists function

PHP built-in function array_key_exists() can determine whether a certain key exists in an array. This function requires two parameters, the first parameter is the key name to be checked, and the second parameter is the array to be checked. This function will return true if the specified key exists in the array, otherwise it will return false.

Sample code:

$arr = array('name' => 'John', 'age' => 30);
if (array_key_exists('name', $arr)) {
  echo "数组中存在 'name' 键";
} else {
  echo "数组中不存在 'name' 键";
}

Execution result:

数组中存在 'name' 键

2. Using isset function

PHP built-in function isset() can be used Determines whether a variable is set and exists in an array. This function can be used to determine whether a certain key exists in an array, and its return value is similar to array_key_exists().

Sample code:

$arr = array('name' => 'John', 'age' => 30);
if (isset($arr['name'])) {
  echo "数组中存在 'name' 键";
} else {
  echo "数组中不存在 'name' 键";
}

Execution result:

数组中存在 'name' 键

It should be noted that if the key value exists but its value is null, the isset() function will return false. Therefore, when using isset() to judge, the type of operator should be determined based on the actual situation.

3. Using the in_array function

The built-in function in_array() can be used to check whether a value already exists in an array. The function will return true if the specified value already exists in the array, false otherwise. Furthermore, if we use the function to check if a value is a key of an array, the function can only be used in PHP5.5 or higher and the third parameter true needs to be added to make the function differentiate between keys and values.

Sample code:

$arr = array('name' => 'John', 'age' => 30);
if (in_array('name', $arr)) {
  echo "存在 'name' 键";
} else {
  echo "不存在 'name' 键";
}

Execution result:

不存在 'name' 键

4. Use array_key_first and array_key_last functions

PHP 7.3 only started to support array_key_first( ) and array_key_last() functions, their function is to return the names of the first key and the last key in the array respectively.

Sample code:

$arr = array('name' => 'John', 'age' => 30);
$first_key = array_key_first($arr);
$last_key = array_key_last($arr);

echo "数组第一个键: " . $first_key . "<br>";
echo "数组最后一个键: " . $last_key;

Execution result:

数组第一个键: name
数组最后一个键: age

With the array_key_first and array_key_last functions, we can determine whether the array is empty by confirming the existence of keys in the array.

Sample code:

$arr1 = array();
$arr2 = array('name' => 'John', 'age' => 30);

if (array_key_first($arr1) === null) {
  echo "数组1为空数组<br>";
}
if (array_key_first($arr2) !== null) {
  echo "数组2不是空数组";
}

Execution result:

数组1为空数组
数组2不是空数组

Summary

This article introduces four methods to determine whether a certain key or index exists in a PHP array , they are array_key_exists(), isset(), in_array() and array_key_first(), array_key_last() functions respectively. These functions are not absolutely good or bad, and the most suitable method should be chosen based on actual project needs. At the same time, we need to pay attention to some details, such as version compatibility when using in_array(). Continuous learning, experimentation, and optimization in practice lead to better programs.

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