1. foreach()
foreach()是一个用来遍历数组中数据的最简单有效的方法。
#example1:
- <?php
- $colors = array ( ' red ' , ' blue ' , ' green ' , ' yellow ' ) ;
- foreach ( $colors as $color ) {
- echo " Do you like $color ? <br /> " ;
- }
- ?>
显示结果:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
2. while()
while() 通常和 list(),each()配合使用。
#example2:
- <?php
- $colors = array ( ' red ' , ' blue ' , ' green ' , ' yellow ' ) ;
- while ( list ( $key , $val ) = each ( $colors )) {
- echo " Other list of $val .<br /> " ;
- }
- ?>
显示结果:
Other list of red.
Other list of blue.
Other list of green.
Other list of yellow.
3. for()
#example3:
- <?php
- $arr = array ( " 0 " => " zero " , " 1 " => " one " , " 2 " => " two " ) ;
- for ( $i = 0 ; $i < count ( $arr ) ; $i ++ ) {
- $str = $arr [ $i ] ;
- echo " the number is $str .<br /> " ;
- }
- ?>
显示结果:
the number is zero.
the number is one.
the number is two.
========= 以下是函数介绍 ==========
key()
mixed key(array input_array)
key()函数返回input_array中位于当前指针位置的键元素。
#example4
- <?php
- $capitals = array ( " Ohio " => " Columbus " , " Towa " => " Des Moines " , " Arizona " => " Phoenix " ) ;
- echo " <p>Can you name the capitals of these states?</p> " ;
- while ( $key = key ( $capitals )) {
- echo $key . " <br /> " ;
- next ( $capitals ) ;
- //每个key()调用不会推进指针。为此要使用next()函数
- }
- ?>
显示结果:
Can you name the capitals of these states?
Ohio
Towa
Arizona
reset()
mixed reset(array input_array)
reset()函数用来将input_array的指针设置回数组的开始位置。如果需要在一个脚本中多次查看或处理同一个数组,就经常使用这个函数,另外这个函数还常用于排序结束时。
#example5 - 在#example1上追加代码
- <?php
- $colors = array ( ' red ' , ' blue ' , ' green ' , ' yellow ' ) ;
- foreach ( $colors as $color ) {
- echo " Do you like $color ? <br /> " ;
- }
- reset ( $colors ) ;
- while ( list ( $key , $val ) = each ( $colors )) {
- echo " $key => $val <br /> " ;
- }
- ?>
显示结果:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
0 => red
1 => blue
2 => green
3 => yellow
注意:将一个数组赋值给另一个数组时会重置原来的数组指针,因此在上例中如果我们在循环内部将 $colors 赋给了另一个变量的话将会导致无限循环。
例如将 $s1 = $colors; 添加到while循环内,再次执行代码,浏览器就会无休止地显示结果。
each()
array each(array input_array)
each()函数返回输入数组当前键/值对,并将指针推进一个位置。返回的数组包含四个键,键0和key包含键名,而键1和value包含相应的数据。如果执行each()前指针位于数组末尾,则返回FALSE。
#example6
- <?php
- $capitals = array ( " Ohio " => " Columbus " , " Towa " => " Des Moines " , " Arizona " => " Phoenix " ) ;
- $s1 = each ( $capitals ) ;
- print_r ( $s1 ) ;
- ?>
显示结果:
Array ( [1] => Columbus [value] => Columbus [0] => Ohio [key] => Ohio )
current(),next(),prev(),end()
mixed current(array target_array)
current()函数返回位于target_array数组当前指针位置的数组值。与next()、prev()、和end()函数不同,current()不移动指针。
next()函数返回紧接着放在当前数组指针的下一个位置的数组值。
prev()函数返回位于当前指针的前一个位置的数组值,如果指针本来就位于数组的第一个位置,则返回FALSE。
end()函数将指针移向target_array的最后一个位置,并返回最后一个元素。
#example7
- <?php
- $fruits = array ( " apple " , " orange " , " banana " ) ;
- $fruit = current ( $fruits ) ; //return "apple"
- echo $fruit . " <br /> " ;
- $fruit = next ( $fruits ) ; //return "orange"
- echo $fruit . " <br /> " ;
- $fruit = prev ( $fruits ) ; //return "apple"
- echo $fruit . " <br /> " ;
- $fruit = end ( $fruits ) ; //return "banana"
- echo $fruit . " <br /> " ;
- ?>
显示结果:
apple
orange
apple
banana
=========== 下面来测试三种遍历数组的速度 ===========
一般情况下,遍历一个数组有三种方法,for、while、foreach。其中最简单方便的是foreach。下面先让我们来测试一下共同遍历一个有50000个下标的一维数组所耗的时间。
测试环境:
Intel Core Due2 2GHz
2GB 1067MHz DDR3
Mac OS X 10.5.7
Apache 2.0.59
MySQL 5.0.41
PHP 5.2.6
#example8
- <?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 /> ' ;
- ?>
测试结果:
Used time of for:0.0228429(s)
Used time of while:0.0544658(s)
Used time of foreach:0.0085628(s)
经过反复多次测试,结果表明,对于遍历同样一个数组,foreach速度最快,最慢的则是while。从原理上来看,foreach是对数组副本进 行操作(通过拷贝数组),而while则通过移动数组内部指标进行操作,一般逻辑下认为,while应该比foreach快(因为foreach在开始执 行的时候首先把数组复制进去,而while直接移动内部指标。),但结果刚刚相反。原因应该是,foreach是PHP内部实现,而while是通用的循 环结构。所以,在通常应用中foreach简单,而且效率高。在PHP5下,foreach还可以遍历类的属性。
http://phpstone.com/the-method-of-traverse-an-array-in-php/?download=list_array01.php