PHP 5 ways to determine if an array is empty

PHP 5 ways to determine if an array is empty

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Source: Code Farm time: 2015-04-22 13:51:11 read:18914

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[Introduction] This article introduced the PHP development encountered in the array problem, here is to judge the PHP array is empty 5 ways, the need for friends can reference.

This article introduced the PHP development encountered in the array problem, here is to judge the PHP array is empty 5 methods, the need for friends can learn from reference.

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.

View Source print? 01. <?php 02. $a  =  ‘‘ ; 03. $a [ ‘c‘ ] =  ‘‘ ; 04. if  (!isset( $a ))  echo  ‘$a 未被初始化‘  .  "" ; 05. if  (!isset( $b ))  echo  ‘$b 未被初始化‘  .  "" ; 06. if  (isset( $a [ ‘c‘ ]))  echo  ‘$a 已经被初始化‘  .  "" ; 07. // 显示结果为 08. // $b 未被初始化 09. // $a 已经被初始化2. Empty function: Detects if 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

View Source print? 1. <?php 2. $a  = 0; 3. $b  =  ‘‘ ; 4. $c  =  array (); 5. if  ( empty empty ( $a ))  echo  ‘$a 为空‘  .  "" ; 6. if  ( empty empty ( $b ))  echo  ‘$b 为空‘  .  "" ; 7. if  ( empty empty ( $c ))  echo  ‘$c 为空‘  .  "" ; 8. if  ( empty empty ( $d ))  echo  ‘$d 为空‘  .  "" ;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.

View Source print? 01. <?php 02. $a  = 0; 03. $b  =  array (); 04. if  ( $a  == null)  echo  ‘$a 为空‘  .  "" ; 05. if  ( $b  == null)  echo  ‘$b 为空‘  .  "" ; 06. if  ( $c  == null)  echo  ‘$b 为空‘  .  "" ; 07. // 显示结果为 08. // $a 为空 09. // $b 为空 10. // Undefined variable: c4. Is_null function: Detects 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

View Source print? 01. <?php 02. $a  = null; 03. $b  = false; 04. if  ( is_null ( $a ))  echo  ‘$a 为NULL‘  .  "" ; 05. if  ( is_null ( $b ))  echo  ‘$b 为NULL‘  .  "" ; 06. if  ( is_null ( $c ))  echo  ‘$c 为NULL‘  .  "" ; 07. // 显示结果为 08. // $a 为NULL 09. // Undefined variable: c5. 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

Summarize:

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."

PHP 5 ways to determine if an array is empty