PHP-Determine if the variable is empty

Solution Objective: determine if a variable is empty

This article has compiled some commonly used in PHP, the judgment variable is empty method, shares to everybody.

1,isset function : Determine whether the variable is initialized

Description: It does not determine if the variable is empty and can be used to determine if the element in the array has been defined

Note: When using isset to determine if an array element is initialized, its efficiency is about 4 times times higher than the array_key_exists.

Copy Code code example:

<?php

$a = ";

$a [' c '] = ';

if (!isset ($a)) echo ' $a not initialized '. "";

if (!isset ($b)) echo ' $b not initialized '. "";

if (isset ($a [' C '])) echo ' $a has been initialized '. "";

Show results as

$b has not been initialized

$a has been initialized

2,empty function : Check whether the variable is "empty"

Description: Any uninitialized variable, a value of 0 or FALSE, or an empty string "" or a null variable, an empty array, an object without any attributes, will be judged as Empty==true

Note 1: Uninitialized variables can also be detected as "empty" by empty

Note that 2:empty can only detect variables and not detect statements

Copy Code code example:

<?php

$a = 0;

$b = ";

$c = Array ();

if (empty ($a)) echo ' $a is empty '. "";

if (empty ($b)) echo ' $b is empty '. "";

if (empty ($c)) echo ' $c is empty '. "";

if (empty ($d)) echo ' $d is empty '. "";

3,var = = null function : Determine if the variable is "empty"

Description: A value of 0 or False or an empty string "" or a null variable, an empty array, will be judged null

Note: A significant difference from empty is that var = = NULL will be an error when the variable is not initialized.

Copy Code code example:

<?php

$a = 0;

$b = Array ();

if ($a = = null) echo ' $a is empty '. "";

if ($b = = null) echo ' $b is empty '. "";

if ($c = = null) echo ' $b is empty '. "";

Show results as

$a is empty

$b is empty

Undefined Variable:c

4,is_null function : Detect if the variable is "null"

Description: The test result is true when the variable is assigned a value of "null"

Note 1:null is case insensitive: $a = null; $a = NULL without any difference

NOTE 2: Test results are true,0, empty strings, false, empty arrays are detected as false only when the value of the variable is "null"

Note 3: The program will error when the variable is not initialized

Copy Code code example:

<?php

$a = null;

$b = false;

if (Is_null ($a)) echo ' $a is null '. "";

if (Is_null ($b)) echo ' $b is null '. "";

if (Is_null ($c)) echo ' $c is null '. "";

Show results as

$a is null

Undefined Variable:c

5. var = = = NULL function : detects if the variable is "null" and the type of the variable must also be "null"

Description: When the variable is assigned a value of "null" and the type of the variable is also "null", the detection result is true

Note 1: On the judgment "null", all equals the same function as Is_null

NOTE 2: The program will error when the variable is not initialized

Summary :

in PHP, "null" and "NULL" are 2 concepts.

Isset is used primarily to determine if a variable has been initialized.

Empty can evaluate to true for variables with a value of false, NULL, 0, NULL, uninitialized.

Is_null only variables with a value of "null" are judged as true

var = = null evaluates to "false", "null", "0", "null" for variables that are true

var = = NULL only evaluates a variable with a value of "null" to True

Note: When judging whether a variable is truly "NULL", most use Is_null to avoid "false", "0" equivalent interference.

This article from "I am a phper, simple and naïve" blog, please be sure to keep this source http://thinkforphp.blog.51cto.com/8733331/1784637

PHP-Determine if the variable is empty