The SplFixedArray class

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

简介

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.

类摘要

class SplFixedArray implements IteratorAggregate, ArrayAccess, Countable, JsonSerializable {

/* 方法 */

public __construct(int $size = 0)

public count(): int

public current(): mixed

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

public getSize(): int

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 setSize(int $size): bool

public toArray(): array

public valid(): bool

public __wakeup(): void

}

更新日志

版本	说明
8.1.0	SplFixedArray implements JsonSerializable now.
8.0.0	SplFixedArray implements IteratorAggregate now. Previously, Iterator was implemented instead.

范例

示例 #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";
}
?>

以上例程会输出：

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::getSize — Gets the size of the array
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::setSize — Change the size of an array
SplFixedArray::toArray — Returns a PHP array from the fixed array
SplFixedArray::valid — Check whether the array contains more elements
SplFixedArray::__wakeup — Reinitialises the array after being unserialised

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User Contributed Notes 7 notes

down

artaxerxes ¶

9 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 ¶

2 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 ¶

12 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 ¶

11 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 ¶

4 years ago


getSize() and count() return the same value

down

-17

Anonymous ¶

4 years ago


PHP Arrays are very fast, and faster overall, especially in PHP7. You almost never need this. There are some cases where using this is better than using arrays but beware that they aren't that obvious.

down

-17

php at stij dot nospam dot npeete dot nospam dot rs dot nl ¶

4 years ago


Note that (as of PHP 7.1) SplFixedArray uses 16 bytes (!) per array item. This can be checked easily via:

<?php
ini_set('memory_limit', '4M');
$array = new SplFixedArray(1000000);
//PHP Fatal error:  Allowed memory size of 4194304 bytes exhausted (tried to allocate 16000000 bytes)
?>

So if you're considering SplFixedArray because you need to use large arrays with very large numbers of items, make sure you have enough memory to support them.

add a note

The SplFixedArray class

简介

类摘要

更新日志

范例

目录

User Contributed Notes 7 notes