Summary of three methods of PHP looping through arrays list (), each (), and while

while (list($key, $value) = each($list)) ｛｝ The performance of writing is higher than foreach,

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①each() function

each() The function needs to pass an array as an argument , Returns the key of the current element in the array / It's worth it , And move the array pointer backward to the next element . key / Value pairs are returned with 4 A mixed array of associations and indexes of elements , The key names are 0、1、key and value. Where key name 0 and key The corresponding value is the same , Is the key name of the array element ,1 and value Contains the values of array elements . If the internal pointer goes past the end of the array , be each() return FALSE.each() The function is used as follows ：

Copy code   The code is as follows :

< ?php 
$contact = array("ID" => 1," full name " => " Gao Mou "," company " => "A company "," Address " => " The Beijing municipal ",); 
$id = each($contact); // Returns an array of $contact The key of the first element in / It's worth it , It's with 4 Array of elements  
print_r($id); // The output array $id：Array([1]=>1,[value]=>1,[0]=>ID,[key]=>ID) 
  
$name = each($contact); // Returns an array of $contact The key of the second element in / It's worth it , It's with 4 Array of elements  
print_r($name); // Output Array([1]=> Gao Mou ,[value]=> Gao Mou ,[0]=> full name ,[key]=> full name ) 
  
$company = each($contact); 
print_r($company); // Output Array([1]=>A company ,[value]=>A company ,[0]=> company ,[key]=> company ) 
  
$address = each($contact); 
print_r($address); // Output Array([1]=> The Beijing municipal ,[value]=> The Beijing municipal ,[0]=> Address ,[key]=> Address ) 
  
$no = each($contact); 
var_dump($no); // Output bool(false) 
?> 

②list() function

This is not really a function , It is PHP The structure of language .list() Assign values to a set of variables in one step , That is, assign the values in the array to some variables .list() Can only be used for arrays with numeric indexes and assume that the array index is from 0 Start . The syntax format is as follows ：

Copy code   The code is as follows :

list(mixed varname,mixed…) = array_expression 

list() Statements are very different from other functions in use , Instead of receiving an array directly as a parameter . But through “=” Operator in the way of assignment , The value of each element in the array , Corresponding assignment list() Every parameter in the function .list() Function converts each parameter in it into a variable that can be used directly in the script . Use as follows ： 

Copy code   The code is as follows :

< ?php 
$info = array('coffee','brown','caffeine'); 
list($drink,$color,$power) = $info; 
  
list($drink,,$power) = $info; // The value of the variable is the first and third value in the array  
  
list( , ,$power) = $info; // The variable value is the value of the third element in the array  
?> 

Learn from the above example list() After the usage of the function , take each() Functions and list() Functions are used together . The code is as follows ：

Copy code   The code is as follows :

< ?php 
$contact = array("ID" => 1," full name " => " Gao Mou "," company " => "A company "," Address " => " The Beijing municipal ",); 
  
list($key,$value) = each($contact); 
echo "$key => $value"; // Output variables $key and $value, In the middle “=>” Division  
?> 

③while loop Traversal array

Previously introduced each() and list() Use of statements , It's not difficult to understand if you use while Loop through the array . The syntax format used is as follows ：

Copy code   The code is as follows :

while(list($key,$value) = each(array_expression)){ 
The loop body  
} 

This union format traverses a given array_expression Array . stay while() Statement in each loop ,each() Statement sets the key of the current array element , Assign to list() The first parameter variable of the function $key. And the value in the current array element , Assign to list() The second parameter variable in the function $value, also each() After the statement is executed, the pointer inside the array will be moved back one step , So next time while() Statement loop , You will get the key of the next element in the array / It's worth it . Until the end of the array each() Statement returns FALSE,while() Statement stops the loop , End the traversal of the array .

Copy code   The code is as follows :

< ?php 
$contact = array( 
"ID" => 1, 
" full name " => " Gao Mou ", 
" company " => "A company ", 
" Address " => " The Beijing municipal ", 
" Telephone " => "[phone]", 
"EMAIL" => "[email protected]", 
); 
  
// With HTML List the information of each element in the array  
echo '<dl> A contact information ：'; 
  
while(list($key,$value) = each($contact)){ 
echo "<dd>$key : $value</dd>"; 
} 
  
echo '</dl>'; 
?> 

It can also be yo on Nested traversal of multidimensional arrays in the same way . although while The result of traversing the array and freach Same statement , But these two methods are different . In the use of while Statement after traversing the array ,each() Statement has pointed the internal pointer of the passed in array parameter to the end of the array . When used again while Statement when traversing the same array , The array pointer is already at the end of the array ,each() Statement returns directly FALSE,while Statement will not be executed in a loop . Only in while Call before execution of statement reset() function , Reassign the array pointer to the first element . and foreach Statement will automatically reset the pointer position of the array , When foreach At the beginning of execution , The pointer inside the array will automatically point to the first cell . This means that there is no need to foreach Loop prior call reset() function .