SplFixedArray主要是处理数组相关的主要功能，与普通php array不同的是，它是固定长度的，且以数字为键名的数组，优势就是比普通的数组处理更快。

看看我本机的Benchmark测试：

ini_set('memory_limit','12800M'); for($size = 10000; $size < 10000000; $size *= 4) { 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;}

结果如下：

Testing size: 10000Array(): 0.004000186920166SplArray(): 0.0019998550415039 Testing size: 40000Array(): 0.017001152038574SplArray(): 0.0090007781982422 Testing size: 160000Array(): 0.050002098083496SplArray(): 0.046003103256226 Testing size: 640000Array(): 0.19701099395752SplArray(): 0.16700983047485 Testing size: 2560000Array(): 0.75704312324524SplArray(): 0.67303895950317

通常情况下SplFixedArray要比php array快上20%~30%，所以如果你是处理巨大数量的固定长度数组，还是强烈建议使用。
SplFixedArray类摘要如下：

SplFixedArray implements Iterator , ArrayAccess , Countable { 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 ) public void __wakeup ( void )}

使用SplFixedArray：

$arr = new SplFixedArray(4);$arr[0] = 'php';$arr[1] = 1;$arr[3] = 'python'; //遍历， $arr[2] 为nullforeach($arr as $v) { echo $v . PHP_EOL;} //获取数组长度echo $arr->getSize(); //4 //增加数组长度$arr->setSize(5);$arr[4] = 'new one'; //捕获异常try{ echo $arr[10];} catch (RuntimeException $e) { echo $e->getMessage();}