Summary analysis of array traversal methods based on PHP_PHP tutorial

1. foreach()
foreach() is the simplest and most effective method for traversing data in an array.
#example1:

Copy code The code is as follows:

$colors= array('red','blue','green','yellow');
foreach ($colorsas$color){
echo "Do you like $color?
}
?>

Display results:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?

2. while()
while() is usually used in conjunction with list() and each().
#example2:

Copy code The code is as follows:

$colors= array('red','blue','green','yellow');
while(list($key,$val)= each($colors)) {
echo "Other list of $val.
";
}
?>

Display results:
Other list of red.
Other list of blue .
Other list of green.
Other list of yellow.

3. for()
#example3:

Copy code The code is as follows:

$arr= array ("0"=> "zero","1"=> "one","2"=> "two") ;
for ($i= 0;$i< count($arr); $i++){
$str= $arr[$i];
echo "the number is $str.< br />";
}
?>

Display the result:
the number is zero.
the number is one.
the number is two.

========== The following is the function introduction==========
key()
mixed key( array input_array)
key() function returns the key element in input_array at the current pointer position.
#example4

Copy code The code is as follows:

$capitals= array("Ohio"=> "Columbus","Towa"=> "Des Moines","Arizona"=> "Phoenix");
echo "

Can you name the capitals of these states?

";
while($key= key($capitals)) {
echo $key."
";
next($capitals );
//Each key() call will not advance the pointer. To do this, use the next() function
}
?>

Display the result:
Can you name the capitals of these states?
Ohio
Towa
Arizona
reset()
mixed reset(array input_array)
reset() function is used to set the pointer of input_array back to the beginning of the array. This function is often used if you need to view or process the same array multiple times in a script. In addition, this function is often used at the end of sorting.
#example5 - Append code on #example1

Copy code The code is as follows:

$colors= array('red','blue','green','yellow');
foreach ($colorsas$color){
echo "Do you like $color?
}
reset($colors);
while(list($key,$val)= each($colors)) {
echo "$key=> $val< br />";
}
?>

Display results:
Do you like red?
Do you like blue?
Do you like green?
Do you like yellow?
0 => red
1 => blue
2 => green
3 => yellow
Note: Assigning one array to another array will reset the original array pointer, so in the above example if we assign $colors to another variable inside the loop, it will result in infinite cycle.
For example, add $s1 = $colors; to the while loop and execute the code again, the browser will display the results endlessly.
each()
array each(array input_array)
each() function returns the current key/value pair of the input array and advances the pointer one position. The returned array contains four keys, key 0 and key contain the key name, and key 1 and value contain the corresponding data. If the pointer is at the end of the array before each() is executed, FALSE is returned.
#example6

Copy code The code is as follows:

$capitals= array(" Ohio"=> "Columbus","Towa"=> "Des Moines","Arizona"=> "Phoenix");
$s1= each($capitals);
print_r($s1 );
?>

Display results:
Array ([1] => Columbus [value] => Columbus [0] => Ohio [key] => Ohio )
current(), next() , prev(), end()
mixed current(array target_array)
current() function returns the array value located at the current pointer position of the target_array array. Unlike the next(), prev(), and end() functions, current() does not move the pointer.
next() function returns the array value placed at the next position of the current array pointer.
The prev() function returns the array value located at the previous position of the current pointer. If the pointer is originally located at the first position of the array, it returns FALSE. The
end() function moves the pointer to the last position of target_array and returns the last element.
#example7

Copy code The code is as follows:

$fruits= array("apple","orange","banana");
$fruit= current($fruits); //return "apple"
echo $fruit."
";
$fruit= next($fruits); //return "orange"
echo $fruit."
";
$fruit= prev($fruits); // return "apple"
echo $fruit."
";
$fruit= end($fruits); //return "banana"
echo $fruit."
";
?>

Display results:
apple
orange
apple
banana
=== ======== Let's test the speed of three traversing arrays ===========
Generally, there are three methods to traverse an array, for, while, foreach. The simplest and most convenient of them is foreach. Let's first test the time it takes to traverse a one-dimensional array with 50,000 subscripts.
Test environment:
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

Copy code The code is as follows:

$arr= array();
for($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)

';
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)
';
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)

';
?>

Test result:
Used time of for:0.0228429(s)
Used time of while:0.0544658(s)
Used time of foreach:0.0085628(s)
After repeated testing, the results It shows that for traversing the same array, foreach is the fastest and the slowest is while. From a principle point of view, foreach operates on a copy of the array (by copying the array), while while operates by moving the internal index of the array. Generally speaking, it is believed that while should be faster than foreach (because foreach first moves the array when it starts to execute. Copied in, while while moves the internal pointer directly), but the result is just the opposite. The reason should be that foreach is an internal implementation of PHP, while while is a general loop structure. Therefore, in general applications, foreach is simple and efficient. Under PHP5, foreach can also traverse the attributes of a class.

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