PHP isset and empty Functions

Isset Usage

• isset() is a PHP function used to check if a variable is set and is not NULL.
• It returns TRUE if the variable exists and has a value other than NULL.
• It returns FALSE if the variable does not exist or is NULL.

Example:

$a = 'hello';
$b = NULL;

isset($a); // returns TRUE
isset($b); // returns FALSE

Is Empty Examples

• empty() is a PHP function used to check if a variable is empty.
• It returns TRUE if the variable is empty (i.e., it does not exist or its value equals FALSE).
• It returns FALSE if the variable is not empty.

Examples:

$a = '';
$b = 'hello';
$c = 0;
$d = NULL;

empty($a); // returns TRUE
empty($b); // returns FALSE
empty($c); // returns TRUE
empty($d); // returns TRUE

Isset Vs Is Null

• isset() and is_null() are two distinct PHP functions:
  • isset() checks if a variable is set and is not NULL.
  • is_null() checks if a variable is NULL.
• isset() is used to check if a variable exists, while is_null() is used to check if a variable is NULL.

Example:

$a = NULL;

isset($a); // returns FALSE
is_null($a); // returns TRUE

Variable Existence Checks

• In PHP, a variable is considered to exist if it has been declared and assigned a value.
• To check if a variable exists, use the isset() function.
• To check if a variable does not exist, use the !isset() function.

Example:

$a = 'hello';

isset($a); // returns TRUE
!isset($b); // returns TRUE, since $b is not declared

Null Coalescing Operator

• The null coalescing operator (??) is a PHP operator used to return the first operand if it exists and is not NULL.
• If the first operand is NULL, it returns the second operand.
• It is used to simplify the process of checking for NULL values.

Example:

$a = 'hello';
$b = NULL;

$c = $a ?? 'default'; // returns 'hello'
$d = $b ?? 'default'; // returns 'default'

Isset Usage

• isset() checks if a variable is set and is not NULL.
• It returns TRUE if the variable exists and has a value other than NULL.
• It returns FALSE if the variable does not exist or is NULL.

Is Empty Examples

• empty() checks if a variable is empty, meaning it does not exist or its value equals FALSE.
• It returns TRUE if the variable is empty.
• It returns FALSE if the variable is not empty.
• Examples of empty values include '', 0, and NULL.

Isset Vs Is Null

• isset() and is_null() are distinct PHP functions.
• isset() checks if a variable is set and is not NULL.
• is_null() checks if a variable is NULL.
• isset() is used to check if a variable exists, while is_null() is used to check if a variable is NULL.

Variable Existence Checks

• A variable is considered to exist if it has been declared and assigned a value.
• isset() is used to check if a variable exists.
• !isset() is used to check if a variable does not exist.

Null Coalescing Operator

• The null coalescing operator (??) returns the first operand if it exists and is not NULL.
• If the first operand is NULL, it returns the second operand.
• It is used to simplify the process of checking for NULL values.
• It can be used to provide a default value when a variable is NULL.