PHP array traversal foreach syntax structure

The foreach syntax structure is used to iterate through an array.

foreach ()

The PHP foreach () syntax structure is used to traverse an operation or an output array, and foreach () can only be used to iterate over an array or an object, resulting in an error when trying to use it for another data type or an uninitialized variable.

Grammar:

foreach (array as $value)    statement//or: foreach (array as $key = = $value)    statement

In the above syntax, each loop assigns the value of the current cell to the $value and the pointer inside the array moves forward one step. In the second syntax format, the key name of the current cell is also assigned to the variable $key in each loop.

Example:

<?php$arr_age = Array ("Wang" =>18, "Li" =>20, "Zhang" =>25); foreach ($arr _age as $age) {    echo $age, ' <br /> ';}? >

Run the example output:

182025

Using array key values

<?php$arr_age = Array ("Wang" =>18, "Li" =>20, "Zhang" =>25); foreach ($arr _age as $key = + $age) {    echo $ Key, ': ', $age, ' <br/> ';}? >

Run the example output:

Wang:18li:20zhang:25

Tips

When foreach starts executing, the pointer inside the array automatically points to the first cell, which means that reset () is not called before the Foreach Loop.

A foreach operation is a copy of the specified array, not the array itself. Changes to the returned array cell do not affect the original array (see example below), but the Foreach loop runs to the end, and the inner pointer of the original array points to the end of the array.

<?php$arr_age = Array ("Wang" =>18, "Li" =>20, "Zhang" =>25); foreach ($arr _age as $age) {    $age = $age +10;
   echo $age, ' <br/> ';} Output original array print_r ($arr _age);? >

Run the example output:

To modify the original array element in foreach, you can do so by reference, changing the example above to:

<?php$arr_age = Array ("Wang" =>18, "Li" =>20, "Zhang" =>25), foreach ($arr _age as & $age) {    $age = $age + Ten;    echo $age, ' <br/> ';} Output original array print_r ($arr _age);? >

Run the example output:

Traversing multidimensional arrays

The foreach syntax structure can only be used to traverse a one-dimensional array, traversing a multidimensional array, typically recursively using foreach nesting or splitting the original array into a one-dimensional array and then a foreach traversal.

Examples of one or two-D array blending:

$arr _age = Array ("Wang" =>18, "Li" =>20, "Zhang" =>array ("name" = "Xiao Zhang", "Age" =>25)); foreach ($arr _age as $ Age) {    if (Is_array ($age)) {        foreach ($age as $detail) {        echo $detail, ' <br/> ';        }    } else {        echo $age, ' <br/> ';    }? >

Run the example output:

1820 Small Sheets 25

The traversal processing of multidimensional arrays is based on the actual data structure and the most appropriate processing method.

Extended read-ahead

The PHP array is implemented through a Hashtable (HashTable) table, so the foreach traversal of the array is based on the order in which the elements are added. If you want to traverse by index size, you should use a for () loop traversal.

for () looping through an array

If you are an array that operates on successive key values , you can also use the for () loop to iterate through the array:

<?php$arr_age = array, $num = count ($arr _age), for ($i = 0; $i < $num; $i + +) {    echo $arr _age[$i]. " <br/> ";}? >

The run example output is as follows:

182025

Tips

You can also use the list () and each () combination to iterate through the array, but the test discovery is less efficient than foreach ().

PHP array traversal foreach syntax structure