Isset, empty, and is_null behavior in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the isset() function check in PHP?

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, otherwise false.

beginner

How does empty() behave with different variable values?

empty() returns true if a variable is not set or its value is considered "empty". This includes 0, "0", "" (empty string), null, false, empty arrays, and unset variables.

intermediate

What is the difference between is_null() and isset()?

is_null() returns true only if the variable's value is exactly null. isset() returns false if the variable is null or not set at all.

beginner

What will empty() return for a variable set to false?

empty() will return true because false is considered an empty value in PHP.

intermediate

If a variable is not declared at all, what will isset() and empty() return?

isset() will return false because the variable does not exist. empty() will return true because the variable is considered empty if not set.

What does isset($var) return if $var = null;?

A true

B Throws an error

C null

D false

isset() returns false if the variable is null.

Which of these values will empty() consider as empty?

A 1

B "0"

C "Hello"

D 42

empty() treats the string "0" as empty.

What does is_null($var) return if $var is not set?

A null

B false

C Throws a warning

D true

is_null() on an unset variable throws a warning about undefined variable.

If $var = false;, what does isset($var) return?

A true

B false

C null

D Depends on PHP version

isset() returns true because $var is set and not null.

Which function returns true for an empty array?

A empty()

B is_null()

C isset()

D None of the above

empty() returns true for empty arrays.

Explain how isset(), empty(), and is_null() differ in checking variable states in PHP.

Think about what each function considers as 'set' or 'empty'.

Describe what happens when you use empty() on a variable that is not declared.

Consider how empty handles unset variables compared to isset.