php check if a certain key exists in an array

In PHP development, we often need to determine whether a certain key exists in an array. This requirement is very common, such as getting the corresponding value based on the key or deleting a specific key-value pair. This article will introduce how to check whether a certain key exists in an array in PHP.

Typically, there are several ways to check whether a key exists in an array:

1. Use the array_key_exists() function

array_key_exists() The function can check whether the specified key exists in an array. This function returns a Boolean value indicating whether the key exists. For example:

$my_array = array(
    'name' => 'Tom',
    'age' => 18,
    'gender' => 'male'
);

if (array_key_exists('name', $my_array)) {
    echo '该键存在！';
} else {
    echo '该键不存在！';
}

In the above code, we use the array_key_exists() function to check whether the array $my_array contains the key name 'name' keys. If it exists, output 'The key exists! ', otherwise output 'The key does not exist! '.

2. Using the isset() function

isset() The isset() function can be used to check whether a variable has been set and is not NULL. When checking a key in an array, the isset()

function returns a Boolean value indicating whether the key exists, or NULL if it exists. For example:

$my_array = array(
    'name' => 'Tom',
    'age' => 18,
    'gender' => 'male'
);

if (isset($my_array['name'])) {
    echo '该键存在！';
} else {
    echo '该键不存在！';
}

In the above code, we check whether the key exists by adding the key name after the array $my_array. If it exists, output 'The key exists! ', otherwise output 'The key does not exist! '

.

It should be noted that when using the isset()

function to check the key, you need to pay attention to distinguish whether it is NULL and whether it exists. For example:

$my_array = array(
    'name' => 'Tom',
    'age' => null,
    'gender' => 'male'
);

if (isset($my_array['name'])) {
    echo '该键存在！';
} else {
    echo '该键不存在！';
}

if (isset($my_array['age'])) {
    echo '该键存在且不为 NULL！';
} else {
    echo '该键不存在或为 NULL！';
}

In the above code, we define an array $my_array, in which the value of the 'age' key is NULL. When using the isset() function to check the 'name' key, 'the key exists! ' because the key exists and is not NULL. When using the isset() function to check the 'age' key, 'the key does not exist or is NULL! '

, even though the key exists because its value is NULL.

3. The difference between using array_key_exists() and isset()

When using array_key_exists() and isset() , there is a difference that needs to be noted: array_key_exists() only determines whether the key exists, while isset() determines whether the key exists and whether the value is NULL. Therefore, if we just want to determine whether the key exists, we can use array_key_exists(). If we need to determine whether the key exists and whether the value is NULL, we can use isset()

. For example:

$my_array = array(
    'name' => 'Tom',
    'age' => null,
    'gender' => 'male'
);

if (array_key_exists('age', $my_array) && $my_array['age'] !== null) {
    echo '该键存在且不为 NULL！';
} else {
    echo '该键不存在或为 NULL！';
}

In the above code, we use the array_key_exists() function to determine whether the 'age' key exists, and also determine whether the value of the key is NULL . If the key exists and is not NULL, output 'The key exists and is not NULL! ', otherwise output 'The key does not exist or is NULL! '

.

Summary

In PHP development, checking whether a certain key exists in an array is a basic task. This article describes three ways to check if a key exists in an array: using the array_key_exists() function, using the isset() function, and array_key_exists() with isset()

difference. You need to choose the most appropriate method to check whether a certain key exists on a case-by-case basis. ###

The above is the detailed content of php check if a certain key exists in an array. For more information, please follow other related articles on the PHP Chinese website!