PHP determines whether the object field is null or undefined

In development, we often need to determine whether a specific field of an object has a value, but this value may be null or undefined. Although both cases indicate no value, they are still different. Therefore, different processing needs to be carried out according to the actual situation when using it.

1. The difference between null and undefined

1. null

null means that the value of a defined object or variable is empty. This is a Assignment mode, indicating that the variable has not been assigned a value. null can also be used in debugging code to indicate that a property has not been assigned correctly. Therefore, when judging whether the attribute value is empty, use the === operator, because it is a strict equality operator and will return true only when the variable data types are the same and the values ​​are equal. For example:

$data = [
    'title' => null,
    'content' => '内容',
];
if ($data['title'] === null) {
    echo '未设置标题';
}

2. undefined

undefined means that the variable has been declared but has not yet been assigned a value. In addition, undefined has the following situations:

(1) The variable does not exist

(2) The object does not have a certain attribute

(3) The function has no return value

If you want to judge a certain Whether the attribute is undefined can be determined by using the isset function or empty function, but it is recommended to use the isset function. For example:

$class = new stdClass();
if (!isset($class->name)) {
    echo '未定义属性name';
}

2. Method to determine whether the object field is null or undefined

When determining whether the object field is null or undefined, you can use the isset function or array_key_exists function to determine. The specific method is as follows:

1. isset function

This function is used to determine whether the variable has been declared and the value is not NULL.

$data = [
    'title' => null,
    'content' => '内容',
];
if (!isset($data['title'])) {
    echo '未设置标题';
}

2. array_key_exists function

This function is used to determine whether a given key name exists in an array. Returns true if the key name exists, false if it does not exist.

$data = [
    'title' => null,
    'content' => '内容',
];
if (!array_key_exists('title', $data)) {
    echo '未设置标题';
}

If you want to determine whether a certain attribute exists in an object, you can use the isset function or the property_exists function to determine. The specific method is as follows:

1. isset function

This function is used to determine whether the variable has been declared and the value is not NULL.

$class = new stdClass();
if (!isset($class->name)) {
    echo '未定义属性name';
}

2. property_exists function

This function is used to determine whether an object has a specified property.

$class = new stdClass();
if (!property_exists($class, 'name')) {
    echo '未定义属性name';
}

3. Summary

In PHP, judging whether an object field is null or undefined is a very important skill and must be carefully mastered in actual development. According to actual needs, you can choose to use the isset function, array_key_exists function, property_exists function, etc. for judgment. Different methods are suitable for different scenarios and should be used flexibly to avoid unnecessary errors.

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