How to use isset() function in php

How to use the isset() function in php: The isset() function is used to detect whether the variable has been set and is not NULL. The specific usage is as follows: [isset($a)]. Returns TRUE if the specified variable exists and is not NULL, otherwise returns FALSE.

isset() function is used to detect whether the variable has been set and is not NULL.

(Recommended tutorial: php graphic tutorial)

If you have used unset() to release a variable, and then pass isset() to judge, it will return FALSE.

If isset() is used to test a variable that is set to NULL, FALSE will be returned.

Also note that the null character ("\0") is not equivalent to PHP's NULL constant.

Function syntax:

bool isset ( mixed $var [, mixed $... ] )

If multiple parameters are passed in at one time, isset() will only return TRUE when all parameters are set. The calculation process is from left to right, and no one is encountered halfway. It will stop immediately when the variable is set.

Return value:

If the specified variable exists and is not NULL, TRUE is returned, otherwise FALSE is returned.

(Learning video recommendation: php video tutorial)

Example:

<?php
$var = &#39;&#39;; 
// 结果为 TRUE，所以后边的文本将被打印出来。
if (isset($var)) {
    echo "变量已设置。" . PHP_EOL;
}
 
$a = "test";
$b = "anothertest"; 
var_dump(isset($a));      // TRUE
var_dump(isset($a, $b)); // TRUE
unset ($a); 
var_dump(isset($a));     // FALSE
var_dump(isset($a, $b)); // FALSE
$foo = NULL;var_dump(isset($foo));   // FALSE
?>

Output result:

变量已设置。
bool(true)
bool(true)
bool(false)
bool(false)
bool(false)

The above is the detailed content of How to use isset() function in php. For more information, please follow other related articles on the PHP Chinese website!