PHP var_sizeof()

This library provides functions to accurately determine the size of any PHP variable in bytes.
By accessing internal PHP structures through FFI, it calculates the memory footprint of variables, aiding developers in efficient memory usage analysis and optimization.
It should be a more accurate tool for calculating the total size of a PHP variable than memory_get_usage(), but it has limitations.

How it works

The var_sizeof() and var_class_sizeof() functions use FFI to access the internal structures of PHP variables.
They calculate the size of internal structures like zval, _zend_array, _zend_object, etc., along with any additional allocated memory for these structures.
However, they do not account for the memory used by handlers, functions, or similar components.

Requirements

PHP >= 7.4 (with FFI)
Linux(x86_64/aarch64) / Darwin(x86_64/arm64)

Usage

composer require mrsuh/php-var-sizeof

<?php

require_once __DIR__ . '/vendor/autoload.php';

$int = 1;
printf("variable \$int size: %d bytes\n", var_sizeof($int));

$array = array_fill(0, 100, $a);
printf("variable \$array size: %d bytes\n", var_sizeof($array));

$object = new \stdClass();
printf("variable \$object size: %d bytes\n", var_sizeof($object));
printf("class \$object size: %d bytes\n", var_class_sizeof($object));

var_sizeof vs memory_get_usage

PHP 8.1.2 Linux(x86_64)

type	var_sizeof(bytes)	memory_get_usage(bytes)
NULL	16	0
boolean(true)	16	0
integer(1)	16	0
double(1.5)	16	0
string("hello world")	27	40
resource	48	416
callable	72	384
array(count: 0, list: true)	336	0
array(count: 100, list: true)	2,128	8,248
array(count: 1,000, list: true)	16,464	36,920
array(count: 10,000, list: true)	262,224	528,440
array(count: 100, list: false)	5,192	8,248
array(count: 1,000, list: false)	41,032	41,016
array(count: 10,000, list: false)	655,432	655,416
EmptyClass{}	72	40
ClassWithArray{"array(count: 0, list: true)"}	408	56
ClassWithArray{"array(count: 100, list: true)"}	2,200	8,304
ClassWithArray{"array(count: 1,000, list: true)"}	16,536	36,976
ClassWithArray{"array(count: 10,000, list: true)"}	262,296	528,496
ClassWithObject{"EmptyClass{}"}	144	96
ArrayIterator{"array(count: 100, list: true)"}	2,264	8,376
ArrayIterator{"array(count: 100, list: false)"}	5,328	40,376

type	var_class_sizeof(bytes)	var_sizeof(bytes)	memory_get_usage(bytes)
EmptyClass{}	1,362	72	40
ClassWithArray{"array(count: 0, list: true)"}	1,494	408	56
ClassWithArray{"array(count: 100, list: true)"}	1,494	2,200	8,304
ClassWithArray{"array(count: 1,000, list: true)"}	1,494	16,536	36,976
ClassWithArray{"array(count: 10,000, list: true)"}	1,494	262,296	528,496
ClassWithObject{"EmptyClass{}"}	1,495	144	96
ArrayIterator{"array(count: 100, list: true)"}	2,437	2,264	8,376
ArrayIterator{"array(count: 100, list: false)"}	2,437	5,328	40,376

Limitations

Works correctly only with userland objects and SPL \ArrayIterator
Does not handle complex structures like extensions, resources, callables, or functions accurately
To calculate the total size of an object, you need to use both var_sizeof() and var_class_sizeof()