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foreach loop usage example code

Jun 23, 2017 am 11:59 AM
foreach code Example cycle usage

在PHP中的foreach是用来进行循环对一个数组的所有元素。

foreach基本语法如下:

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foreach ($array_variable as $value)

{

[code to execute]

}

or

FOREACH ($array_variable as $key => $value)

{

[code to execute]

}

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在这两种情况下,多次[代码执行]将被处死是等于在$ array_variable数组元素的个数。
让我们来看一个例子。假设我们有下面的代码段:

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$array1 = array(1,2,3,4,5);

FOREACH ($array1 as $abc)

{

print "new value is " . $abc*10 . "<br>";

}

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输出结果
new value is 10
new value is 20
new value is 30
new value is 40
new value is 50
foreach循环以上经历了所有5个元素的数组$ array1,每次打印出一份声明中含有10倍的数组元素的值。
foreach作用是遍历当前数组的所有值出来并且赋给$var
官方给出的实例代码:

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<?php

/* foreach example 1: value only */

$a = array(1, 2, 3, 17);

foreach ($a as $v) {

echo "

Current

 value of \$a: $v.\n";

}

/* foreach example 2: value (with key printed for illustration) */

$a = array(1, 2, 3, 17);

$i = 0; /* for illustrative purposes only */

foreach ($a as $v) {

echo "\$a[$i] => $v.\n";

$i++;

}

/* foreach example 3: key and value */

$a = array(

"one" => 1,

"two" => 2,

"three" => 3,

"seventeen" => 17

);

foreach ($a as $k => $v) {

echo "\$a[$k] => $v.\n";

}

/* foreach example 4: multi-dimensional arrays */

$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";

}

}

/* foreach example 5: dynamic arrays */

foreach (array(1, 2, 3, 4, 5) as $v) {

echo "$v\n";

}

?>

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再来看一个foreach 对多维数据操作实例

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$s = array(array(1,2),array(3,4),array(5,6));

foreach( $s as $v => $_v )

{

foreach( $_v as $vc => $_vc )

{

echo $_vc[0],&#39;|&#39;.$_vc[1],&#39;<br />&#39;;

//print_r($_vc);

}

}

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先来看一下foreach的语法:

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foreach ($array as $key=>$value)

{

……

}

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为了便于理解,我们假定这里的$array是一个一维的相关数组,$key是数组的索引,$value是这个索引的值,它们的名字可以随意,之所以叫$key和$value是为了便于理解。为了能让你更好的理解foreach的工作过程,我们来创建一个数组:
$array = array('first'=>'ibm','second'=>'hp');
现在我们模拟PHP服务用foreach对$array进行遍历:

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foreach ($array as $key=>$value)

{

echo $key.&#39;=>&#39;.$value;

}

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第一次循环,$key = 'first',$value = 'ibm',这个时候,实际foreach对$array执行了一个我们看不见的操作:next($array),将数组指针向前(这里的“向前”跟PHP手册相同,不是我们通常所理解的“向前”)移一。然后echo语句输出"first=>ibm"。
第二次循环,首先会判断数组$array的当前指针是否已经到了数组的末尾,如果是,结束循环,否则进入第二次循环。当然这样的判断在进入第一次循环的时候也会有,如果$array是一个空数组,那么就会直接执行循环下面的语句。此时,$key = 'second','value' = 'hp',next($array)后,输出"second=>hp"。然后进行判断,数组指针已经到达末尾,执行下面的语句。
到这里你应该对foreach循环有所了解了吧?还有一点需要的是,foreach每次只是传递一个值,而不是真的对数组元素进行操作。具体到上面的例子,如果你想在每个数组元素的后面加上 'company' 这个字符串,那么$value .= 'company'这样的操作是不行的,它并不会改变数组元素的值,这个时候你应该这样用:$array[$key] .= 'company';

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