5_PHP数组_3_数组处理函数及其应用_5_数组遍历语言结构

以下为学习孔祥盛主编的《PHP编程基础与实例教程》（第二版）所做的笔记。

数组遍历语言结构

1. foreach ( array as $value )

程序：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $value) {
     echo $value."<br/>";
 }
 ?>

输出：

music
movie
computer
software

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

程序：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $key=>$value) {
     echo $key."=>".$value."<br/>";
 }
 ?>

输出：

2=>music
5=>movie
1=>computer
6=>software

foreach 语言结构除了可以实现对数组的遍历，还可以实现数组元素的键或值的修改。

以下程序1、程序2、程序3，只有程序1、2实现了数组元素值的修改。

程序1：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $key=>&$value) {    //注意这里的 &$value
     $value = "I like ".$value;
 }
 print_r($interests);
 //Array ( [2] => I like music [5] => I like movie [1] => I like computer [6] => I like software )
 ?>

输出：

Array ( [2] => I like music [5] => I like movie [1] => I like computer [6] => I like software )

程序2：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $key=>$value) {
     $interests[$key] = "I like ".$value;
 }
 print_r($interests);
 ?>

输出：

Array ( [2] => I like music [5] => I like movie [1] => I like computer [6] => I like software )

程序3：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $key=>$value) {
     $value = "I like ".$value;
 }
 print_r($interests);
 ?>

输出：

Array ( [2] => music [5] => movie [1] => computer [6] => software )

foreach 语言结构操作的是数组的一个拷贝，而不是数组本身。在foreach 遍历数组的过程，尽量不要使用数组指针函数操作 “当前指针”（current），否则会事与愿违。

程序：

 <?php
 $interests[2] = "music";
 $interests[5] = "movie";
 $interests[1] = "computer";
 $interests[] = "software";
 foreach ( $interests as $key=>$value) {
     echo "I like ".current($interests)."!<br/>";
     echo $value."<br/>";
 }
 print_r($interests);
 ?>

输出：

I like music!
music
I like music!
movie
I like music!
computer
I like music!
software
Array ( [2] => music [5] => movie [1] => computer [6] => software )