PHP 5 ways to determine if an array is empty _php tutorial

PHP 5 ways to determine if an array is empty

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.

 
 

  
  

  
 
  
  

  
$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 not initialized  
  
  

  
//$a has been initialized  
 
 

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

 
 

  
  

  
 
  
  

  
$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 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.

 
 

  
  

  
 
  
  

  
$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: 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

 
 

  
  

  
 
  
  

  
$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

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."

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