PHP's foreach Traversal array

Foreach

(PHP 4, PHP 5)

The foreach construct provides an easy way to iterate over arrays. foreach works is on arrays and objects, and'll issue an error while you try to use it in a variable with a different Da TA type or an uninitialized variable. There are two syntaxes:

foreach (array_expression as $value)
    statement
foreach (array_expression as $key => $value)
    statement

The loops over the array given by Array_expression. On each iteration, the value of the ' is ' assigned to $value and the internal array pointer was advanced by on E (so on the next iteration, and you'll be looking at the next element).

The second form would additionally assign the current element's key to the $key variable in each iteration.

It is possible to customize object iteration.

Note:

When foreach-A-starts executing, the internal array pointer is automatically reset to the ' the ' array. This means so you don't need to call reset () before a foreach loop.

As foreach relies on the internal array pointer, changing it within the loop may leads to unexpected behavior.

In order to is able to directly modify array elements within the loop precede $value with. In this case the value is assigned by reference.

$arr = array(1, 2, 3, 4);
foreach ($arr as &$value) {
$value = $value * 2;
}
// $arr is now array(2, 4, 6, 8)
unset($value); // break the reference with the last element
?>

Referencing $value is only possible if the iterated array can be referenced (i.e. if it's a variable). The following code won ' t work:

foreach (array(1, 2, 3, 4) as &$value) {
$value = $value * 2;
}
?>Warning

Reference of a $value and the last array element, remain even after the Foreach loop. It is recommended to destroy it by unset ().

Note:

foreach does not support the ability to suppress error messages using ' @ '.

You may have noticed the following are functionally identical:

$arr = array("one", "two", "three");
reset($arr);
while (list(, $value) = each($arr)) {
echo "Value: $value
\n";
}

foreach ($arr as $value) {
echo "Value: $value
\n";
}
?>

The following are also functionally identical:

$arr = array("one", "two", "three");
reset($arr);
while (list($key, $value) = each($arr)) {
echo "Key: $key; Value: $value
\n";
}

foreach ($arr as $key => $value) {
echo "Key: $key; Value: $value
\n";
}
?>

Some more examples to demonstrate usage:

-->/* Foreach Example 1:value only * *

$a = Array (1, 2, 3, 17);

foreach ($a as $v) {
echo "Current value of \ $a: $v. \ n";
}

/* foreach example 2:value (with their manual access notation printed for illustration) * *

$a = Array (1, 2, 3, 17);

$i = 0; /* For illustrative purposes only * *

foreach ($a as $v) {
echo "\ $a [$i] => $v. \ n";
$i + +;
}

/* Foreach example 3:key and value * *

$a = Array (
"One" => 1,
"Two" => 2,
"Three" => 3,
"Seventeen" => 17
);

foreach ($a as $k => $v) {
echo "\ $a [$k] => $v. \ n";
}

/* foreach Example 4:multi-dimensional arrays * *
$a = array ();
$a [0][0] = "a";
$a [0][1] = "B";
$a [1][0] = "Y";
$a [1][1] = "Z";

foreach ($a as $v 1) {
foreach ($v 1 as $v 2) {
echo "$v 2\n";
}
}

/* foreach Example 5:dynamic arrays * *

foreach (Array (1, 2, 3, 4, 5) as $v) {
echo "$v \ n";
}
?>

Unpacking nested arrays with list ()

(PHP 5 >= 5.5.0)

PHP 5.5 added the ability to iterate over an array of arrays and unpack the nested array into loop variables by providing A list () as the value.

For example:

$array = [
[1, 2],
[3, 4],
];

foreach ($array as list($a, $b)) {
// $a contains the first element of the nested array,
// and $b contains the second element.
echo "A: $a; B: $b\n";
}
?>

The above example would output:

a:1; B:2
A:3; B:4

can provide fewer elements in the list () than there are in the nested array, in which case the leftover array values W Ill be ignored:

$array = [
[1, 2],
[3, 4],
];

foreach ($array as list($a)) {
// Note that there is no $b here.
echo "$a\n";
}
?>

The above example would output:

1
3

A notice would be generated if there aren ' t enough array elements to fill the list ():

$array = [
[1, 2],
[3, 4],
];

foreach ($array as list($a, $b, $c)) {
echo "A: $a; B: $b; C: $c\n";
}
?>

The above example would output:

notice:undefined Offset:2 in example.php to line 7
a:1; B:2; C: 

notice:undefined offset:2 in example.php on line 7