How to determine whether a variable is empty in php

How to determine whether a variable is empty in php: You can use the isset() function to determine. The isset() function is used to detect whether a variable has been set and is not NULL. If a variable has been released using the unset() function, it will return FALSE through the isset() function.

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

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If you have used unset() to release a variable, and then pass isset() to judge, it will return FALSE. If you use isset() to test a variable that is set to NULL, it will return FALSE.

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

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 setting is encountered halfway. variable will stop immediately.

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Return value:

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

Code 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;
}
// 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));
// TRUEvar_dump(isset($a, $b)); // TRUE
unset ($a);
var_dump(isset($a));
// FALSEvar_dump(isset($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)

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