PHP遍历数组的方法及效率对比

foreach ( array_expression as $value ) statement
/* array_expression是要遍历的数组
   as作用是将数组的值赋给$value
   statement是后续语句
*/

<?php
 '白色' ,
  'black' => '黑色' ,
  'red' => '红色' ,
  'green' => '绿色',
  'yellow' => '黄色');
 foreach( $color as $c) echo $c ."
";    
?>

foreach ( array_expression as $key => $value ) statement

foreach( $color as $c) echo $c ."<br>";

foreach( $color as $key => $c) echo $key.$c ."<br>";

<?php 
 $a[]="张学友"; /* 定义数组 */
 $a[]="刘德华";
 $a[]="黎明";
 $a[]="郭富城";
 $s=count($a); /* 统计数组个数 */
 for($i=0;$i<$s;$i++){ /* 遍历数组 */
  echo $a[$i] ."<br /-->"; /* 显示数组 */
 }
?>

<?php 
    $urls= array('aaa','bbb','ccc','ddd'); 
    while(list($key,$val)= each($urls)) { 
      echo "This Site url is $val.<br />"; 
    } 
?>

<?php
  $arr= array();
  for($i= 0; $i< 50000; $i++){
  $arr[]= $i*rand(1000,9999);
  }
  function GetRunTime()
  {
  list($usec,$sec)=explode(" ",microtime());
  return ((float)$usec+(float)$sec);
  }
  ######################################
  $time_start= GetRunTime();
  for($i= 0; $i< count($arr); $i++){
  $str= $arr[$i];
  }
  $time_end= GetRunTime();
  $time_used= $time_end- $time_start;
  echo 'Used time of for:'.round($time_used, 7).'(s)<br /><br />';
  unset($str, $time_start, $time_end, $time_used);
  ######################################
  $time_start= GetRunTime();
  while(list($key, $val)= each($arr)){
  $str= $val;
  }
  $time_end= GetRunTime();
  $time_used= $time_end- $time_start;
  echo 'Used time of while:'.round($time_used, 7).'(s)<br /><br />';
  unset($str, $key, $val, $time_start, $time_end, $time_used);
  ######################################
  $time_start= GetRunTime();
  foreach($arr as$key=> $val){
  $str= $val;
  }
  $time_end= GetRunTime();
  $time_used= $time_end- $time_start;
  echo 'Used time of foreach:'.round($time_used, 7).'(s)<br /><br />';
?>

Used time of for:0.0228429(s)
Used time of while:0.0544658(s)
Used time of foreach:0.0085628(s)