PHP isset () function uses the [turn]

PHP isset () function

isset () function for detecting whether a variable is set and a non-NULL.

If, after use has been unset () released a variable, then through isset () determines the return FALSE.

When using isset () test is a variable set to NULL and returns FALSE.

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

PHP Version: PHP 4, PHP 5, PHP 7

grammar

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

Parameter Description:

• $ Var: variable to be detected.

If a number of parameters passed, then isset () only returns TRUE when all the parameters are set, the calculation from left to right, half-way encounter variable is not set will stop immediately.

return value

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

<?php
$var = '';
 
// 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($a));      // TRUE
var_dump(isset($a, $b)); // TRUE
 
unset ($a);
 
var_dump(isset($a));     // FALSE
var_dump(isset($a, $b)); // FALSE
 
$foo = NULL;
var_dump(isset($foo));   // FALSE
?>

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