php finds whether a certain value exists in an array

In PHP, array is a very common data structure that can store multiple related data items. In actual development, we often need to find whether a certain value exists in an array. This article will introduce several methods of finding array elements in PHP and discuss their advantages and disadvantages.

Method 1: in_array function

The in_array function can be used to determine whether an element exists in an array. Its syntax is as follows:

bool in_array ( mixed $needle , array $ haystack [, bool $strict = FALSE ] )

Among them, $needle indicates the element to be found, $haystack indicates the array to be found, and $strict indicates whether to enable type comparison. When $strict is true, it is judged whether the value and type of the element are completely equal.

The sample code is as follows:

<?php $fruits = array('apple', 'banana', 'orange');
if (in_array('apple', $fruits)) {
    echo '存在';
} else {
    echo '不存在';
}
?>

In this example, the 'apple' element exists in the $fruits array, so the output 'exists'

Disadvantages: Although the in_array function is simple and easy Used, but it only returns whether the element exists, and cannot directly obtain the key value of the element.

Method 2: array_key_exists function

The array_key_exists function can be used to check whether the specified key name or index exists in the array. The syntax is as follows:

bool array_key_exists (mixed $key, array $array)

Among them, $key represents the key name or index to be searched, and $array represents the array to be searched.

The sample code is as follows:

<?php $fruits = array('a' => 'apple', 'b' => 'banana', 'o' => 'orange');
if (array_key_exists('a', $fruits)) {
    echo '存在';
} else {
    echo '不存在';
}
?>

In this example, there is an element with the key name 'a' in the $fruits array, so the output 'exists'

Disadvantages: array_key_exists The function only returns whether the key name exists, and cannot obtain the value of the element.

Method 3: Combining in_array and array_search

Combining the in_array and array_search functions can achieve the purpose of finding element values ​​and key names at the same time. The in_array function is used to find element values, and the array_search function is used to find key names.

The sample code is as follows:

<?php $fruits = array('a' => 'apple', 'b' => 'banana', 'o' => 'orange');
if (($key = array_search('banana', $fruits)) !== false) {
    echo '存在，键名为' . $key;
} else {
    echo '不存在';
}
?>

In this example, there is an element with the value 'banana' in the $fruits array, so the output 'exists, key name b'.

Disadvantages: You need to execute the in_array function first, and then execute the array_search function if it exists, which is less efficient. At the same time, it is also impossible to judge special cases such as key name 0 or false, which are regarded as non-existent.

Method 4: foreach loop

Use a foreach loop to traverse the array and find whether the specified element exists one by one. When an element is found, the value and key name of the element can be obtained directly.

The sample code is as follows:

<?php $fruits = array('a' => 'apple', 'b' => 'banana', 'o' => 'orange');
foreach($fruits as $key => $value) {
    if ($value == 'banana') {
        echo '存在，键名为' . $key;
        break;
    }
}
?>

In this example, there is an element with the value 'banana' in the $fruits array, so the output 'exists, key name b'.

Advantages: You can obtain the value and key name of the element at the same time, avoiding the problem of judgment failure due to special circumstances such as key name 0 or false.

To sum up, we can choose different methods to find elements in the array according to actual needs. If you just need to determine whether an element exists, you can use the in_array function. If you need to get the key name of an element, you can use the array_key_exists function. If you need to get the value and key name of an element at the same time, you can use in_array and array_search together, or use a foreach loop to traverse the array.

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