数据结构
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The SplFixedArray class

(PHP 5 >= 5.3.0)

简介

The SplFixedArray class provides the main functionalities of array. The main differences between a SplFixedArray and a normal PHP array is that the SplFixedArray is of fixed length and allows only integers within the range as indexes. The advantage is that it allows a faster array implementation.

类摘要

SplFixedArray implements Iterator , ArrayAccess , Countable {
/* 方法 */
public __construct ([ int $size = 0 ] )
public int count ( void )
public mixed current ( void )
public static SplFixedArray fromArray ( array $array [, bool $save_indexes = true ] )
public int getSize ( void )
public int key ( void )
public void next ( void )
public bool offsetExists ( int $index )
public mixed offsetGet ( int $index )
public void offsetSet ( int $index , mixed $newval )
public void offsetUnset ( int $index )
public void rewind ( void )
public int setSize ( int $size )
public array toArray ( void )
public bool valid ( void )
}

范例

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";
}
?>

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

Table of Contents

数据结构
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PHP手册 - N: The SplFixedArray class

用户评论:

alex dot andrienko at gmail dot com (15-Nov-2010 10:13)

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".

nairbv AT yahoo DOT com (21-Oct-2009 10:08)

Though, object creation overhead means this method is slower for small arrays.

for example, if the other posters benchmark script is changed to a more realistic:

<?php
$elements = 20;
for($size = 1000; $size < 50000000; $size *= 2) {
    echo PHP_EOL . "Testing size: $size" . PHP_EOL;
    for($s = microtime(true), $i = 0; $i < $size; $i++) {
        for($j=0,$container=array();$j < $elements; $j++ ) {
            $container[$i] = NULL;
        }
    }
    echo "Array(): " . (microtime(true) - $s) . PHP_EOL;

    for($s = microtime(true), $i = 0; $i < $size; $i++) {
        for( $j=0,$container=new SplFixedArray($elements);$j<$elements;$j++) {
            $container[$i] = NULL;
        }
    }
    echo "SplArray(): " . (microtime(true) - $s) . PHP_EOL;
}

we get:

Testing size: 1000
Array(): 0.0030221939086914
SplArray(): 0.0041899681091309

Testing size: 2000
Array(): 0.0060598850250244
SplArray(): 0.0083701610565186

Testing size: 4000
Array(): 0.012003898620605
SplArray(): 0.016681909561157

Testing size: 8000
Array(): 0.024173021316528
SplArray(): 0.033347129821777

Testing size: 16000
Array(): 0.048118829727173
SplArray(): 0.066897869110107

Testing size: 32000
Array(): 0.096546173095703
SplArray(): 0.13370203971863

Testing size: 64000
Array(): 0.1932430267334
SplArray(): 0.26755595207214

Testing size: 128000
Array(): 0.38473010063171
SplArray(): 0.5374698638916

Testing size: 256000
Array(): 0.77228307723999
SplArray(): 1.0708079338074

Testing size: 512000
Array(): 1.5438990592957
SplArray(): 2.1406710147858

Testing size: 1024000
Array(): 3.0910761356354
SplArray(): 4.3108429908752

Testing size: 2048000
Array(): 6.1561989784241
SplArray(): 8.612802028656

......

chrisstocktonaz at gmail dot com (14-Jul-2009 07:07)

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