The SplFixedArray class

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

Introduction

The SplFixedArray class provides the main functionalities of array. The main difference between a SplFixedArray and a normal PHP array is that the SplFixedArray must be resized manually and allows only integers within the range as indexes. The advantage is that it uses less memory than a standard array.

Class synopsis

class SplFixedArray implements IteratorAggregate, ArrayAccess, Countable, JsonSerializable {

/* Methods */

public __construct(int $size = 0)

public count(): int

public current(): mixed

public static fromArray(array $array, bool $preserveKeys = true): SplFixedArray

public getIterator(): Iterator

public getSize(): int

public jsonSerialize(): array

public key(): int

public next(): void

public offsetExists(int $index): bool

public offsetGet(int $index): mixed

public offsetSet(int $index, mixed $value): void

public offsetUnset(int $index): void

public rewind(): void

public __serialize(): array

public setSize(int $size): true

public toArray(): array

public __unserialize(array $data): void

public valid(): bool

public __wakeup(): void

}

Changelog

Version	Description
8.2.0	The SplFixedArray::__serialize() and SplFixedArray::__unserialize() magic methods have been added to SplFixedArray.
8.1.0	SplFixedArray implements JsonSerializable now.
8.0.0	SplFixedArray implements IteratorAggregate now. Previously, Iterator was implemented instead.

Examples

Example #1 SplFixedArray usage example

<?php
// Initialize the array with a fixed length
$array = new SplFixedArray(5);

$array[1] = 2;
$array[4] = "foo";

var_dump($array[0]); // NULL
var_dump($array[1]); // int(2)

var_dump($array["4"]); // string(3) "foo"

// Increase the size of the array to 10
$array->setSize(10);

$array[9] = "asdf";

// Shrink the array to a size of 2
$array->setSize(2);

// The following lines throw a RuntimeException: Index invalid or out of range
try {
    var_dump($array["non-numeric"]);
} catch(RuntimeException $re) {
    echo "RuntimeException: ".$re->getMessage()."\n";
}

try {
    var_dump($array[-1]);
} catch(RuntimeException $re) {
    echo "RuntimeException: ".$re->getMessage()."\n";
}

try {
    var_dump($array[5]);
} catch(RuntimeException $re) {
    echo "RuntimeException: ".$re->getMessage()."\n";
}
?>

The above example will output:

NULL
int(2)
string(3) "foo"
RuntimeException: Index invalid or out of range
RuntimeException: Index invalid or out of range
RuntimeException: Index invalid or out of range

SplFixedArray::__construct — Constructs a new fixed array
SplFixedArray::count — Returns the size of the array
SplFixedArray::current — Return current array entry
SplFixedArray::fromArray — Import a PHP array in a SplFixedArray instance
SplFixedArray::getIterator — Retrieve the iterator to go through the array
SplFixedArray::getSize — Gets the size of the array
SplFixedArray::jsonSerialize — Returns a representation that can be converted to JSON
SplFixedArray::key — Return current array index
SplFixedArray::next — Move to next entry
SplFixedArray::offsetExists — Returns whether the requested index exists
SplFixedArray::offsetGet — Returns the value at the specified index
SplFixedArray::offsetSet — Sets a new value at a specified index
SplFixedArray::offsetUnset — Unsets the value at the specified $index
SplFixedArray::rewind — Rewind iterator back to the start
SplFixedArray::__serialize — Serializes the SplFixedArray object
SplFixedArray::setSize — Change the size of an array
SplFixedArray::toArray — Returns a PHP array from the fixed array
SplFixedArray::__unserialize — Deserializes the data parameter into an SplFixedArray object
SplFixedArray::valid — Check whether the array contains more elements
SplFixedArray::__wakeup — Reinitialises the array after being unserialised

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User Contributed Notes 6 notes

down

artaxerxes ¶

12 years ago

As the documentation says, SplFixedArray is meant to be *faster* than array. Do not blindly believe other people's benchmarks, and beextra careful with the user comments on php.net. For instance, nairbv's benchmark code is completely wrong. Among other errors, it intends to increase the size of the arrays, but always initialize a 20 elements SplFixedArray.

On a PHP 5.4 64 bits linux server, I found SplFixedArray to be always faster than array().
* small data (1,000):
    * write: SplFixedArray is 15 % faster
    * read:  SplFixedArray is  5 % faster
* larger data (512,000):
    * write: SplFixedArray is 33 % faster
    * read:  SplFixedArray is 10 % faster

down

herhor67 at interia dot pl ¶

4 years ago

Memory usage for arrays of 1132766 ints (data derived from some 1kx1k img):
Regular:  76453160B (67.5B/int)
SplFixed: 18898744B (16.7B/int)

In my application, SFA uses 75% less RAM, which is a life-saver.

Speed comparison:
Regular: 449ms
SplFixed (resized before every element): 791ms
SplFixed (fully preallocated): 392ms
SplFixed (preall-d to 1M and then resized): 547ms

Pros and cons:
+ much more efficient RAM-wise
+ a bit faster if max size is known
~ a bit slower if max size is only approximated
- much slower if max size is not known
- cannot be used with most array functions

To sum up:
SplFixedArray is a very good choice for storing giant amount of data, though only as long as you at least roughly know the size and can work without array functions.

down

chrisstocktonaz at gmail dot com ¶

15 years ago

Note, that this is considerably faster and should be used when the size of the array is known. Here are some very basic bench marks:



<?php

for($size = 1000; $size < 50000000; $size *= 2) {

    echo PHP_EOL . "Testing size: $size" . PHP_EOL;

    for($s = microtime(true), $container = Array(), $i = 0; $i < $size; $i++) $container[$i] = NULL;

    echo "Array(): " . (microtime(true) - $s) . PHP_EOL;



    for($s = microtime(true), $container = new SplFixedArray($size), $i = 0; $i < $size; $i++) $container[$i] = NULL;

    echo "SplArray(): " . (microtime(true) - $s) . PHP_EOL;

}

?>



OUTPUT

Testing size: 1000

Array(): 0.00046396255493164

SplArray(): 0.00023293495178223



Testing size: 2000

Array(): 0.00057101249694824

SplArray(): 0.0003058910369873



Testing size: 4000

Array(): 0.0015869140625

SplArray(): 0.00086307525634766



Testing size: 8000

Array(): 0.0024251937866211

SplArray(): 0.00211501121521



Testing size: 16000

Array(): 0.0057680606842041

SplArray(): 0.0041120052337646



Testing size: 32000

Array(): 0.011334896087646

SplArray(): 0.007631778717041



Testing size: 64000

Array(): 0.021990060806274

SplArray(): 0.013560056686401



Testing size: 128000

Array(): 0.053267002105713

SplArray(): 0.030976057052612



Testing size: 256000

Array(): 0.10280108451843

SplArray(): 0.056283950805664



Testing size: 512000

Array(): 0.20657992362976

SplArray(): 0.11510300636292



Testing size: 1024000

Array(): 0.4138810634613

SplArray(): 0.21826505661011



Testing size: 2048000

Array(): 0.85640096664429

SplArray(): 0.46247816085815



Testing size: 4096000

Array(): 1.7242450714111

SplArray(): 0.95304894447327



Testing size: 8192000

Array(): 3.448086977005

SplArray(): 1.96746301651

down

alex dot andrienko at gmail dot com ¶

14 years ago

Memory footprint of splFixedArray is about 37% of a regular "array" of the same size. 
I was hoping for more, but that's also significant, and that's where you should expect to see difference, not in "performance".

down

Anonymous ¶

6 years ago

getSize() and count() return the same value

down

CK ¶

1 year ago

Be warned that SplFixedArray does not provide all of the main functionalities of array. For example, it does not support array_slice. SplFixedArray should be far more efficient at supporting such array operations than normal arrays (since it should be simply a contiguous slice). Check that all your main array functions are really supported before trying to use SplFixedArray instead of array. With JIT in PHP8, some loops to polyfill these are perhaps now realistic, but still not as fast as native functions.

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The SplFixedArray class

Introduction

Class synopsis

Changelog

Examples

Table of Contents

Improve This Page

User Contributed Notes 6 notes