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Resources

Description

A resource is a special variable, holding a reference to an external resource. Resources are created and used by special functions.

See also the get_resource_type() function.

– PHP Reference

Example: resource type

<?php

$filePath = __DIR__ . DIRECTORY_SEPARATOR . 'file.txt';
$someFile = fopen($filePath, 'r');

if ($someFile === false) {
    die('Unable to open file');
}

print("Information:\n");
var_dump($someFile);
print('Type: ' . gettype($someFile) . PHP_EOL);
print("As string: {$someFile}\n\n");

$content = fread($someFile, filesize($filePath));
print("Content: {$content}\n");

fclose($someFile);

print("Information:\n");
var_dump($someFile);
print('Type: ' . gettype($someFile) . PHP_EOL);
print("As string: {$someFile}\n\n");

Result (PHP 8.4):

Information:
resource(5) of type (stream)
Type: resource
As string: Resource id #5

Content: Some content.

Information:
resource(5) of type (Unknown)
Type: resource (closed)
As string: Resource id #5

Source code: Example

Usage

A resource is a special variable that references to an external resource such as:

a file
a database connection
a network connection

A resource is not actual data like a string or number. Instead, it’s a reference to something outside of PHP. PHP uses resources to manage things outside of PHP efficiently by automatically free it when it is no longer in use.

– PHP Tutorial

Converting to `resource`

As resource variables hold special handles to opened files, database connections, image canvas areas and the like, converting to a resource makes no sense.

Freeing resources

Thanks to the reference-counting system being part of Zend Engine, a resource with no more references to it is detected automatically, and it is freed by the garbage collector. For this reason, it is rarely necessary to free the memory manually.

Note: Persistent database links are an exception to this rule. They are not destroyed by the garbage collector.