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
    #[\Deprecated]
    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

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    User Contributed Notes 6 notes

    up
    52
    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
    up
    8
    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.
    up
    21
    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
    up
    11
    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".
    up
    4
    Anonymous
    6 years ago
    getSize() and count() return the same value
    up
    1
    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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