How to delete a variable in PHP
There are three ways to delete defined variables in PHP:
- unset($var)
- $var = (unset)$var
- $var = null
Only the first of these ways actually deletes the variable completely. The other two, set it to NULL, which means that the variable no longer has a value, but in principle still exists. Accessing this would not generate the error “variable does not exist”.
Example: “unset($var)” vs “(unset)$var” vs “$var = null”
In this example the variables $var1, $var2 and $var3 are defined identically.
<?php
// Defining sample variables
$var1 = 'variable 1';
$var2 = 'variable 2';
$var3 = 'variable 3';
// Output the three variables before deleting
var_dump($var1, $var2, $var3);
// Delete variables
unset($var1);
$var2 = (unset)$var2;
$var3 = null;
// Output variables after deleting
// var1 should get an error because it was completely deleted
var_dump($var1, $var2, $var3);
// List all currently available variables
var_dump(get_defined_vars());
?>
Output:
string(10) "variable 1"
string(10) "variable 2"
string(10) "variable 3"
Notice: Undefined variable: var1 in [...][...] on line 17
NULL
NULL
NULL
array(6) {
["_GET"]=>
array(0) {
}
["_POST"]=>
array(0) {
}
["_COOKIE"]=>
array(0) {
}
["_FILES"]=>
array(0) {
}
["var2"]=>
NULL
["var3"]=>
NULL
}
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