Common method for PHP to determine if an array is empty (five methods)

This article introduced the PHP development encountered in the array problem, small series here to you summed up 5 methods about PHP to determine whether the array is empty, need to refer to the friend

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.

<?php$a = '; $a [' c '] = '; if (!isset ($a)) echo ' $a uninitialized '. ""; if (!isset ($b)) echo ' $b not initialized '. "; if (isset ($a [' C '])) echo ' $a has been initialized '. "";//The display result is//$b uninitialized//$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

<?php$a = 0; $b = '; $c = array (); if (empty ($a)) echo ' $a empty '. ""; if (empty ($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.

<?php$a = 0; $b = array (); if ($a = = null) echo ' $a is empty '. "", if ($b = = null) echo ' $b is empty '. ""; if ($c = = null) echo ' $b is empty '. "";//The result is//$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

<?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 ' $c is null '. "";//Display the result is//$a for 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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