is_resource

(PHP 4, PHP 5, PHP 7)

is_resource — Finds whether a variable is a resource

Description

bool is_resource ( mixed $var )

Finds whether the given variable is a resource.

Parameters

var: The variable being evaluated.

Return Values

Returns TRUE if var is a resource, FALSE otherwise.

Examples

Example #1 is_resource() example


<?php

$db_link = @mysql_connect('localhost', 'mysql_user', 'mysql_pass');
if (!is_resource($db_link)) {
    die('Can\'t connect : ' . mysql_error());
}

?>

Notes

Note:
is_resource() is not a strict type-checking method: it will return FALSE if var is a resource variable that has been closed.

User Contributed Notes

btleffler [AT] gmail [DOT] com

4 years ago


I was recently trying to loop through some objects and convert them to arrays so that I could encode them to json strings.

I was running into issues when an element of one of my objects was a SoapClient. As it turns out, json_encode() doesn't like any resources to be passed to it. My simple fix was to use is_resource() to determine whether or not the variable I was looking at was a resource.

I quickly realized that is_resource() returns false for two out of the 3 resources that are typically in a SoapClient object. If the resource type is 'Unknown' according to var_dump() and get_resource_type(), is_resource() doesn't think that the variable is a resource!

My work around for this was to use get_resource_type() instead of is_resource(), but that function throws an error if the variable you're checking isn't a resource.

So how are you supposed to know when a variable is a resource if is_resource() is unreliable, and get_resource_type() gives errors if you don't pass it a resource?

I ended up doing something like this:

<?php

function isResource ($possibleResource) { return !is_null(@get_resource_type($possibleResource)); }

?>

The @ operator suppresses the errors thrown by get_resource_type() so it returns null if $possibleResource isn't a resource.

I spent way too long trying to figure this stuff out, so I hope this comment helps someone out if they run into the same problem I did.

CertaiN

2 years ago


Try this to know behavior:

<?php
function resource_test($resource, $name) {
    echo 
        '[' . $name. ']',
        PHP_EOL,
        '(bool)$resource => ',
        $resource ? 'TRUE' : 'FALSE',
        PHP_EOL,
        'get_resource_type($resource) => ',
        get_resource_type($resource) ?: 'FALSE',
        PHP_EOL,
        'is_resoruce($resource) => ',
        is_resource($resource) ? 'TRUE' : 'FALSE',
        PHP_EOL,
        PHP_EOL
    ;
}
 
$resource = tmpfile();
resource_test($resource, 'Check Valid Resource');
 
fclose($resource);
resource_test($resource, 'Check Released Resource');
 
$resource = null;
resource_test($resource, 'Check NULL');
?>

It will be shown as...

[Check Valid Resource]
(bool)$resource => TRUE
get_resource_type($resource) => stream
is_resoruce($resource) => TRUE

[Check Released Resource]
(bool)$resource => TRUE
get_resource_type($resource) => Unknown
is_resoruce($resource) => FALSE

[Check NULL]
(bool)$resource => FALSE
get_resource_type($resource) => FALSE
Warning:  get_resource_type() expects parameter 1 to be resource, null given in ... on line 10
is_resoruce($resource) => FALSE