What is the usage of unset() in php

In PHP, the unset() function is mainly used to destroy a given variable. The syntax is "unset (variable to be destroyed)" and there is no return value. If you unset() a global variable in a function, only the local variable is destroyed, and the variables in the calling environment will retain the same value before calling unset().

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

#You must log out after using an array variable This variable

unset() — Unsets the given variable.

void unset ( mixed $var [, mixed $... ] )

unset() Destroys the specified variable.

The behavior of unset() in a function will vary depending on the type of variable you want to destroy.

If you unset() a global variable in a function, only the local variable will be destroyed, and the variables in the calling environment will maintain the same value before calling unset().

<?php
function destroy_foo() {
    global $foo;
    unset($foo);
}

$foo = &#39;bar&#39;;
destroy_foo();
echo $foo;
?>

The above example only works inside the function.

If you unset() a static variable in a function, the static variable will be destroyed inside the function. However, when this function is called again, this static variable will be restored to the value it had before it was last destroyed.

<?php
function foo()
{
    static $bar;
    $bar++;
    echo "Before unset: $bar, ";
    unset($bar);
    $bar = 23;
    echo "after unset: $bar\n";
}
 
foo();
foo();
foo();
?>

The above routine will output:

Before unset: 1, after unset: 23
Before unset: 2, after unset: 23
Before unset: 3, after unset: 23

Recommended learning: "PHP Video Tutorial"

The above is the detailed content of What is the usage of unset() in php. For more information, please follow other related articles on the PHP Chinese website!