PHP null value detection functions and methods

This article explains the PHP null value detection function and method. We will detect the parameters carried by almost any entry HTTP request. Functions similar to isset() empty() must not be uncommon.

The following test results are based on whether PHP7.16

is defined: isset()

You can use the isset() function to determine whether a variable is defined, an element in the array Whether it has been initialized, its efficiency is about 4 times higher than array_key_exists()

$a = 'test';
 
$b = array('key1' => 'value1');
 
$class = new stdClass();
 
var_dump(isset($class->test->test)); // 判断对象属性是否定义：输出 bool(false)
 
var_dump(isset($a)); // 判断变量是否定义：输出 bool(true)
 
var_dump(isset($c)); // 判断变量是否定义：输出 bool(false)
 
var_dump(isset($b['key1'])); // 判断数组元素是否定义：输出 bool(true)
 
var_dump(isset($b['key2'])); // 判断数组元素是否定义：输出 bool(false)

Judge whether it is empty: empty( )

empty() function, detects whether the variable is empty

Any uninitialized quantity, 0, false, empty string, null, empty array, using empty to judge will return true

var_dump(empty($c)); // 输出 bool(true)
 
var_dump(empty($b['key2'])); // 输出 bool(true)
 
var_dump(empty($class)); // 输出 bool(false)
 
var_dump($class); // 输出 object(stdClass)#1 (0) {}
 
var_dump(empty($class->test->test)); // 输出 bool(true)
 
class EmptyClass{};
 
$empty_class = new EmptyClass();
 
var_dump(empty($empty_class));// 输出 bool(false)
 
null == $var 判断

#In addition to judging undefined variables, an error will be reported. It is the same as empty judgment, 0, false, empty array, etc. will all be reported. Returning true means that the == expression will perform automatic type conversion on the variables on both sides, so the result is true.

is_null judgment

When the single variable assignment is null or NULL, the judgment result is true, otherwise it is false. If the variable is not defined, an error will be reported

null === $var determines the

expression: === is mandatory type detection. It not only detects the values ​​of the variables on both sides of the expression, but also detects the types of the variables. True will be returned only if they are equal.

0 === $var: Check whether it is 0

false === $var: Check whether it is false

null === $var: Check whether it is false null

'' === $var: Check whether it is an empty string. It will return false if it contains any characters, such as space characters. \0

Using === can make a good distinction. Empty strings, 0, false and null, and even integers and floating point types can be distinguished.

$zero_int = 0;
 
$zero_bool = false;
 
$zero_double = 0.0;
 
$zero_null = null;
 
$zero_str = '';
 
var_dump(0 === $zero_int); // 输出 bool(true)
 
var_dump(0 === $zero_bool); // 输出 bool(false)
 
var_dump(0 === $zero_double); // 输出 bool(false)
 
var_dump(0 === $zero_null); // 输出 bool(false)
 
var_dump(0 === $zero_str); // 输出 bool(false)
 
var_dump('' === $zero_str); // 输出 bool(true)
 
var_dump('' === $zero_int); // 输出 bool(false)
 
var_dump('' === $zero_bool); // 输出 bool(false)
 
var_dump(0.0 === $zero_double);// 输出 bool(true)
 
var_dump(0.0 === $zero_int); // 输出 bool(false)

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