PHP用foreach遍历数组比较高效

foreach()有两种用法：

foreach(array_name as $value)    
{       
	statement;    
}

这里的array_name是你要遍历的数组名，每次循环中，array_name数组的当前元素的值被赋给$value,并且数组内部的下标向下移一 步，也就是下次循环回得到下一个元素。

foreach(array_name as $key => $value)    
{        
	statement;      
} 

这里跟第一种方法的区别就是多了个$key,也就是除了把当前元素的值赋给$value外，当前元素的键值也会在每次循环中被赋给变量$key。键值可以 是下标值，也可以是字符串。比如book[0]=1中的"0"，book[id]="001"中的"id".

程序实例：

1

<?php
/*-------------------------------------------------------------------------*/
/* foreach example 1: value only */
echo "foreach example 1: value only ".'<br />';
$a = array(1, 2, 3, 17);
foreach ($a as $v) {
   echo "Current value of ".$a.":". $v."<br />";
}
?>
// 运行结果
foreach example 1: value only 
Current value of $a: 1
Current value of $a: 2
Current value of $a: 3
Current value of $a: 17

2

/*-------------------------------------------------------------------------*/
/* foreach example 2: value (with key printed for illustration) */
echo '<br />'.'<br />'."foreach example 2: value (with key printed for illustration) ".'<br />';
$a = array(1, 2, 3, 17);
$i = 0; /* for illustrative purposes only */
foreach ($a as $v) {
    echo ""$a[$i] => $v".'<br />';
    $i++;
}
// 程序运行结果
foreach example 2: value (with key printed for illustration) 
$a[0] => 1
$a[1] => 2
$a[2] => 3
$a[3] => 17

3

/*-------------------------------------------------------------------------*/
/* foreach example 3: key and value */
echo '<br />'.'<br />'."foreach example 3: key and value ".'<br />';
$a = array(
    "one" => 1,
    "two" => 2,
    "three" => 3,
    "seventeen" => 17
);
foreach ($a as $k => $v) {
    echo ""$a[$k] => $v".'<br />';
}
// 程序运行结果
foreach example 3: key and value 
$a[one] => 1
$a[two] => 2
$a[three] => 3
$a[seventeen] => 17

4

/*-------------------------------------------------------------------------*/
/* foreach example 4: multi-dimensional arrays */
echo '<br />'.'<br />'."foreach example 4: multi-dimensional arrays ".'<br />';
$a = array();
$a[0][0] = "a";
$a[0][1] = "b";
$a[1][0] = "y";
$a[1][1] = "z";
foreach ($a as $v1) {
    foreach ($v1 as $v2) {
        echo "$v2"n";
    }
}
// 程序运行结果
foreach example 4: multi-dimensional arrays 
a b y z

5

/*-------------------------------------------------------------------------*/
/* foreach example 5: dynamic arrays */
echo '<br />'.'<br />'."foreach example 5: dynamic arrays ".'<br />';
foreach (array(1, 2, 3, 4, 5) as $v) {
    echo "$v"n";
}
// 程序运行结果
foreach example 5: dynamic arrays 
1 2 3 4 5

也可以这么用：

$messageNav['首页'] =ROOT_PATH;
$messageNav['人才交流'] ="#"
$messageNav['动态专栏'] ="hragent/cn/"
<?php $i = 0;foreach ($messageNav as $key=>$value):?>
<?php if ($i != count($messageNav) - 1):?>
<a href="<?=$value?>"><?=$key?></a>> 
<?php else:?>
<a href="<?=$value?>" class="onlink"><?=$key?></a>
<?php endif;?>
<?php $i++;endforeach;?>