{"id":2550,"date":"2021-09-05T08:09:51","date_gmt":"2021-09-05T08:09:51","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=2550"},"modified":"2025-04-06T05:11:08","modified_gmt":"2025-04-06T05:11:08","slug":"php-isset","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-tutorial\/php-isset\/","title":{"rendered":"PHP isset"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn how to use the PHP isset()<\/code> construct to check if a variable is set and not null.<\/p>\n\n\n\n

Introduction to the PHP isset() construct #<\/a><\/h2>\n\n\n\n

PHP isset()<\/code> returns true<\/code> if a variable is set and not null<\/a>.<\/p>\n\n\n

isset<\/span>(mixed $var): bool<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example will result in an error:<\/p>\n\n\n
<?php<\/span>\n\n$f = isset<\/span>;<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Error:<\/p>\n\n\n
PHP Parse error:  syntax error, unexpected ';'<\/span>, expecting '('<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
To work around it, you can create a function that uses the isset()<\/code> construct and call that function using the variable functions. For example:<\/p>\n\n\n
<?php<\/span>\n\nfunction<\/span> isset_and_not_null<\/span>($var)<\/span>: bool<\/span>\n<\/span>{\n    return<\/span> isset<\/span>($var);\n}<\/span><\/code><\/span>Code language:<\/span> HTML, XML<\/span> (<\/span>xml<\/span>)<\/span><\/small><\/pre>\n\n\n
$isset = fn($var) => isset<\/span>($var);\n\nvar_dump($isset($count)) \/\/ false<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following returns false<\/code> because the $count<\/code> variable has not been declared:<\/p>\n\n\n
<?php<\/span>\n\nvar_dump(isset<\/span>($count));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example returns true<\/code> because the $count<\/code> variable is declared, and its value is different than null:<\/p>\n\n\n
<?php<\/span>\n\n$count = 0<\/span>;\nvar_dump(isset<\/span>($count));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(true<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If you assign null<\/code> to a variable and pass it to the isset()<\/code>, the isset()<\/code> will return false<\/code>:<\/p>\n\n\n
<?php<\/span>\n\n$count = null<\/span>;\nvar_dump(isset<\/span>($count));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If you unset a variable, the variable becomes unset. Therefore, the isset()<\/code> will return false<\/code>:<\/p>\n\n\n
<?php<\/span>\n\n$count = 0<\/span>;\nunset<\/span>($count);\nvar_dump(isset<\/span>($count));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Using PHP isset with an array #<\/a><\/h2>\n\n\n\n
If you pass an array<\/a> element to isset()<\/code>, it’ll return true<\/code>. For example:<\/p>\n\n\n
<?php<\/span>\n\n$colors = ['primary'<\/span> => 'blue'<\/span>];\n\nvar_dump(isset<\/span>($colors['primary'<\/span>]));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(true<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
However, if you pass a non-existing element to isset()<\/code>, it’ll return false<\/code>. For example:<\/p>\n\n\n
<?php<\/span>\n\n$colors = ['primary'<\/span> => 'blue'<\/span>];\n\nvar_dump(isset<\/span>($colors['secondary'<\/span>]));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(true<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If you pass an array element with value null to isset()<\/code>, The isset()<\/code> will return false<\/code>:<\/p>\n\n\n
<?php<\/span>\n\n$colors = ['primary'<\/span> => 'blue'<\/span>,'secondary'<\/span> => null<\/span>];\n\nvar_dump(isset<\/span>($colors['secondary'<\/span>]));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
PHP isset() with string offsets #<\/a><\/h2>\n\n\n\n
The isset()<\/code> works with string offsets. For example:<\/p>\n\n\n
<?php<\/span>\n\n$message = 'Hello'<\/span>;\nvar_dump(isset<\/span>($message[0<\/span>]));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(true<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
If you pass a string element with an invalid offset, the isset()<\/code> will return false<\/code>. For example:<\/p>\n\n\n
<?php<\/span>\n\n$message = 'Hello'<\/span>;\nvar_dump(isset<\/span>($message[strlen($message)]));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
PHP isset() with multiple variables #<\/a><\/h2>\n\n\n\n
The isset()<\/code> accepts multiple variables and returns true<\/code> if all variables are set. The isset()<\/code> It evaluates the variables from left to right and stops when encountering an unset variable.<\/p>\n\n\n
isset<\/span>(mixed $v1, mixed $v2, ...): bool<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following example returns true<\/code> because all variables $x<\/code>, $y<\/code> and $z<\/code> are set:<\/p>\n\n\n
<?php<\/span>\n\n$x = 10<\/span>;\n$y = 20<\/span>;\n$z = 30<\/span>;\n\nvar_dump(isset<\/span>($x, $y, $z));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(true<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
However, the following example returns false<\/code> because the variable $y<\/code> is null<\/code>, which is not set. Also, the isset()<\/code> won’t evaluate the variable $z<\/code>:<\/p>\n\n\n
<?php<\/span>\n\n$x = 10<\/span>;\n$y = null<\/span>;\n$z = 30<\/span>;\n\nvar_dump(isset<\/span>($x, $y, $z));<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
bool(false<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
    \n
  • isset()<\/code> is a language construct, not a function.<\/li>\n\n\n\n
  • isset()<\/code> returns true<\/code> if a variable is set and not null.<\/li>\n\n\n\n
  • isset()<\/code> returns true<\/code> if an array element exists and is not null.<\/li>\n\n\n\n
  • isset()<\/code> returns true<\/code> if a string index is valid or false otherwise.<\/li>\n\n\n\n
  • isset()<\/code> returns true<\/code> if all variables are set and not null. It’ll stop evaluating once it encounters an unset variable.<\/li>\n<\/ul>\n
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    Did you find this tutorial useful?<\/div>\n\t\t
    \n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t Yes <\/span>\n\t\t\t<\/button>\n\n\t\t\t\n\t\t\t\t\n\t\t\t\t\t<\/path>\n\t\t\t\t<\/svg>\n\t\t\t\t No <\/span>\n\t\t\t<\/button>\n\t\t<\/div>\n\t<\/header>\n\n\t
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    <\/div>\n\t\t\t\n\t\t\t
Try it<\/a><\/p>\n\n\n\n
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Note that you’ll learn about the arrow function syntax in the later tutorial<\/a>.<\/p>\n\n\n\n
Or it’s shorter if you use the arrow function<\/a> syntax:<\/p>\n\n\n
The isset()<\/code> is a language construct, not a function<\/a>. Therefore, you cannot assign it to a variable<\/a>, return it from a function, or call it dynamically via a variable function<\/a>.<\/p>\n\n\n\n