How to use php isset

php isset function is used to detect whether a variable is set. Its syntax is "bool isset (mixed $var [, mixed $...] )". The parameter "var" represents the variable to be checked. If isset is used Testing a variable set to NULL will return FALSE.

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PHP isset() Function

Definition and usage

isset() — Check whether a variable is set.

Syntax

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

Check whether the variable is set and not NULL.

If a variable has been released using unset(), it will no longer be isset(). If you use isset() to test a variable that is set to NULL, it will return FALSE. Also note that a NULL byte ("\0") is not equivalent to PHP's NULL constant.

Parameters

var The variable to be checked.

Return value: TRUE if var exists and the value is not NULL, otherwise FALSE.

PHP version: PHP 4, PHP 5, PHP 7

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 "This var is set so I will print.";
}
// 在后边的例子中，我们将使用 var_dump 输出 isset() 的返回值。
// the return value of isset().
$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
?>

Run result:

This var is set so I will print.bool(true) bool(true) bool(false) bool(false) bool(false)

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