5 ways for PHP to determine whether an array is empty

1. isset function: Determine whether the variable is initialized

Description: It does not determine whether the variable is empty and can be used to determine whether the elements in the array have been defined

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

 
  
  

  
   
   
<?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 '. "";
  
   
   
Display results as
  
   
   
$b has not been initialized
  
   
   
$a has been initialized
 
  
  

2. Empty function: Detect whether the variable is "empty"

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

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

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

 
  
  

  
   
   
<?php
  
   
   
$a = 0;
  
   
   
$b = ';
  
   
   
$c = Array ();
  
   
   
if (Emptyempty ($a)) echo ' $a is empty '. "";
  
   
   
if (Emptyempty ($b)) echo ' $b is empty '. "";
  
   
   
if (Emptyempty ($c)) echo ' $c is empty '. "";
  
   
   
if (Emptyempty ($d)) echo ' $d is empty '. "";
 
  
  

3. var = null function: Determine whether the variable is "null"

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

Note: The significant difference from empty is that var = null will error when the variable is uninitialized.

 
  
  

  
   
   
<?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 '. "";
  
   
   
Display results as
  
   
   
$a is empty
  
   
   
$b is empty
  
   
   
Undefined Variable:c
 
  
  

4. Is_null function: Detect whether the variable is "null"

Note: The test result is true when the variable is assigned "null"

Note that 1:null is case-insensitive: $a = null; $a = NULL without any distinction

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

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

 
  
  

  
   
   
<?php
  
   
   
$a = null;
  
   
   
$b = false;
  
   
   
if (Is_null ($a)) echo ' $a null '. "";
  
   
   
if (Is_null ($b)) echo ' $b null '. "";
  
   
   
if (Is_null ($c)) echo ' $c null '. "";
  
   
   
Display results as
  
   
   
$a is null
  
   
   
Undefined Variable:c
 
  
  

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

Note: When the variable is assigned "null" and the type of the variable is also "null", the test result is true

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

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

Summarize:

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

Isset is primarily used to determine whether a variable has been initialized

Empty can judge a value of "false", "empty", "0″," null, "uninitialized" as true

Is_null only evaluates to TRUE for a variable with a value of "null"

var = null evaluates to TRUE for variables with a value of "false", "null", "0″", "null"

var = = null evaluates to true only for variables that have a value of ' null '

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