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Questions and Answers
What is the purpose of the isset() function in PHP?
What is the purpose of the isset() function in PHP?
What will be the result of isset($a) if $a is not declared?
What will be the result of isset($a) if $a is not declared?
What is the purpose of the empty() function in PHP?
What is the purpose of the empty() function in PHP?
What will be the result of empty($a) if $a is an empty string?
What will be the result of empty($a) if $a is an empty string?
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What is the difference between isset() and is_null()?
What is the difference between isset() and is_null()?
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What will be the result of isset($a) if $a is NULL?
What will be the result of isset($a) if $a is NULL?
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What is the purpose of the null coalescing operator (??) in PHP?
What is the purpose of the null coalescing operator (??) in PHP?
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What will be the result of $a ?? 'default' if $a is an empty string?
What will be the result of $a ?? 'default' if $a is an empty string?
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How can you check if a variable does not exist in PHP?
How can you check if a variable does not exist in PHP?
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What is the result of isset($a) if $a is declared but not assigned a value?
What is the result of isset($a) if $a is declared but not assigned a value?
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Study Notes
Isset Usage
-
isset()is a PHP function used to check if a variable is set and is not NULL. - It returns
TRUEif the variable exists and has a value other than NULL. - It returns
FALSEif 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
TRUEif the variable is empty (i.e., it does not exist or its value equals FALSE). - It returns
FALSEif 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()andis_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, whileis_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
TRUEif the variable exists and has a value other than NULL. - It returns
FALSEif 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
TRUEif the variable is empty. - It returns
FALSEif the variable is not empty. - Examples of empty values include
'',0, andNULL.
Isset Vs Is Null
-
isset()andis_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, whileis_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.
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Description
Learn about the isset and empty functions in PHP. Understand how to use them to check if a variable is set, not NULL, or empty.
