PHP：如何检查var是否已初始化？ 当var设置为NULL时，isset返回false

Question

<?php
    $var = NULL;

    var_dump(isset($var)); // bool(false)
    var_dump(isset($unset_var)); // bool(false)
?>

isset($var) should return TRUE, since it has been set to NULL.

Is there any way to check for this?

Thanks!

Answer 1

use get_defined_vars() to get an array of the variables defined in the current scope and then test against it with array_key_exists();

Edited:

if you wanted a function to test existence you would create one like so:

function varDefined($name,$scope) {
  return array_key_exists($name, $scope);
}

and use like so in any given scope:

$exists = varDefined('foo',get_defined_vars());

Should work for any scope.