What is the difference between isset() and empty() in PHP?
Jun 13, 2025 am 12:25 AM
In PHP, isset() and empty() are used to check variable states, but have different uses. 1. isset() checks whether the variable is set and not null, and returns true even if the value is an empty string, 0 or false; 2. empty() checks whether the variable is empty, including empty string, 0, "0", null, false, empty array, etc., which are all considered "empty" and return true; 3. Use isset() to determine whether the variable exists, and use empty() to determine whether the variable has valid data; 4. For example, check whether the form field isset() to verify whether the field is not empty; 5. In special cases, if "0" is regarded as empty by empty(), the object has no attributes, it is still considered non-empty. Pay attention to these differences to avoid logical errors. The two are not interchangeable and should be selected according to your needs.
In PHP, isset() and empty() are both used to check variable states, but they do very different things — especially when it comes to what they consider "valid" or "meaningful" data.
What isset() really checks for
The isset() function checks whether a variable is set and is not null . That means even if the value is something like 0 , false , or an empty string "" , as long as it's been assigned, isset() will return true .
Examples:
-
isset($var)returnsfalseif$varhas never been declared. - If
$var = null;,isset($var)returnsfalse. - If
$var = 0;,isset($var)returnstrue.
So isset() is more about existence than content.
How empty() behaves differently
On the other hand, empty() checks if a variable is "empty" , which in PHP terms include:
-
""(empty string) -
0(integer zero) -
"0"(string zero) -
null -
false -
[](empty array)
If any of these values ??are passed to empty() , it will return true . So empty() is stricter when it comes to considering what counts as "nothing."
Example:
$var = 0;
if (empty($var)) {
// This block runs because 0 is considered "empty"
}When to use each one
Use isset() when you want to know if a variable has been set at all — regardless of its value.
Use empty() when you're checking if a variable actually contains meaningful data.
Here's a quick guide:
- Need to check if a form field was submitted? → Use
isset(). - Need to verify that a field isn't blank or zero? → Use
empty(). - Want to avoid notices/warnings when accessing possible undefined variables? →
isset()helps with that too.
They can also be used together, depending on your logic needs.
A few edge cases worth noting
Some tricky values ??behave differently than you might expect:
-
"0"(a string containing only zero) →empty()says it's empty. - An object with no properties →
empty()considers it not empty. - Arrays with only empty elements → Still considered non-empty unless fully empty (
[]).
These little quirks matter when validating user input or handling API responses.
So basically, isset() asks “is this variable there?” while empty() asks “does this variable have anything useful?” They're close but definitely not interchangeable.
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