PHP: Arrays - Manual
source link: https://www.php.net/manual/en/language.types.array.php
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Syntax ¶
Specifying with array() ¶
An array can be created using the array()
language construct. It takes any number of comma-separated
key => value
pairs
as arguments.
array( key => value, key2 => value2, key3 => value3, ... )
The comma after the last array element is optional and can be omitted. This is usually done
for single-line arrays, i.e. array(1, 2)
is preferred over
array(1, 2, )
. For multi-line arrays on the other hand the trailing comma
is commonly used, as it allows easier addition of new elements at the end.
Note:
A short array syntax exists which replaces
array()
with[]
.
Example #1 A simple array
<?php
$array = array(
"foo" => "bar",
"bar" => "foo",
);
// Using the short array syntax
$array = [
"foo" => "bar",
"bar" => "foo",
];
?>
The key can either be an int or a string. The value can be of any type.
Additionally the following key casts will occur:
-
Strings containing valid decimal ints, unless the number is preceded by a
+
sign, will be cast to the int type. E.g. the key"8"
will actually be stored under8
. On the other hand"08"
will not be cast, as it isn't a valid decimal integer. -
Floats are also cast to ints, which means that the
fractional part will be truncated. E.g. the key
8.7
will actually be stored under8
. -
Bools are cast to ints, too, i.e. the key
true
will actually be stored under1
and the keyfalse
under0
. -
Null will be cast to the empty string, i.e. the key
null
will actually be stored under""
. -
Arrays and objects can not be used as keys.
Doing so will result in a warning:
Illegal offset type
.
If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten.
Example #2 Type Casting and Overwriting example
<?php
$array = array(
1 => "a",
"1" => "b",
1.5 => "c",
true => "d",
);
var_dump($array);
?>
The above example will output:
array(1) { [1]=> string(1) "d" }
As all the keys in the above example are cast to 1
, the value will be overwritten
on every new element and the last assigned value "d"
is the only one left over.
PHP arrays can contain int and string keys at the same time as PHP does not distinguish between indexed and associative arrays.
Example #3 Mixed int and string keys
<?php
$array = array(
"foo" => "bar",
"bar" => "foo",
100 => -100,
-100 => 100,
);
var_dump($array);
?>
The above example will output:
array(4) { ["foo"]=> string(3) "bar" ["bar"]=> string(3) "foo" [100]=> int(-100) [-100]=> int(100) }
The key is optional. If it is not specified, PHP will use the increment of the largest previously used int key.
Example #4 Indexed arrays without key
<?php
$array = array("foo", "bar", "hello", "world");
var_dump($array);
?>
The above example will output:
array(4) { [0]=> string(3) "foo" [1]=> string(3) "bar" [2]=> string(5) "hello" [3]=> string(5) "world" }
It is possible to specify the key only for some elements and leave it out for others:
Example #5 Keys not on all elements
<?php
$array = array(
"a",
"b",
6 => "c",
"d",
);
var_dump($array);
?>
The above example will output:
array(4) { [0]=> string(1) "a" [1]=> string(1) "b" [6]=> string(1) "c" [7]=> string(1) "d" }
As you can see the last value "d"
was assigned the key
7
. This is because the largest integer key before that
was 6
.
Example #6 Complex Type Casting and Overwriting example
This example includes all variations of type casting of keys and overwriting of elements.
<?php
$array = array(
1 => 'a',
'1' => 'b', // the value "a" will be overwritten by "b"
1.5 => 'c', // the value "b" will be overwritten by "c"
-1 => 'd',
'01' => 'e', // as this is not an integer string it will NOT override the key for 1
'1.5' => 'f', // as this is not an integer string it will NOT override the key for 1
true => 'g', // the value "c" will be overwritten by "g"
false => 'h',
'' => 'i',
null => 'j', // the value "i" will be overwritten by "j"
'k', // value "k" is assigned the key 2. This is because the largest integer key before that was 1
2 => 'l', // the value "k" will be overwritten by "l"
);
var_dump($array);
?>
The above example will output:
array(7) { [1]=> string(1) "g" [-1]=> string(1) "d" ["01"]=> string(1) "e" ["1.5"]=> string(1) "f" [0]=> string(1) "h" [""]=> string(1) "j" [2]=> string(1) "l" }
Accessing array elements with square bracket syntax ¶
Array elements can be accessed using the array[key]
syntax.
Example #7 Accessing array elements
<?php
$array = array(
"foo" => "bar",
42 => 24,
"multi" => array(
"dimensional" => array(
"array" => "foo"
)
)
);
var_dump($array["foo"]);
var_dump($array[42]);
var_dump($array["multi"]["dimensional"]["array"]);
?>
The above example will output:
string(3) "bar" int(24) string(3) "foo"
Note:
Prior to PHP 8.0.0, square brackets and curly braces could be used interchangeably for accessing array elements (e.g.
$array[42]
and$array{42}
would both do the same thing in the example above). The curly brace syntax was deprecated as of PHP 7.4.0 and no longer supported as of PHP 8.0.0.
Example #8 Array dereferencing
<?php
function getArray() {
return array(1, 2, 3);
}
$secondElement = getArray()[1];
?>
Note:
Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an
E_NOTICE
-level error message will be issued, and the result will benull
.
Note:
Array dereferencing a scalar value which is not a string yields
null
. Prior to PHP 7.4.0, that did not issue an error message. As of PHP 7.4.0, this issuesE_NOTICE
; as of PHP 8.0.0, this issuesE_WARNING
.
Creating/modifying with square bracket syntax ¶
An existing array can be modified by explicitly setting values in it.
This is done by assigning values to the array, specifying the
key in brackets. The key can also be omitted, resulting in an empty pair of
brackets ([]
).
$arr[key] = value; $arr[] = value; // key may be an int or string // value may be any value of any type
If $arr doesn't exist yet or is set to null
or false
, it will be created, so this is
also an alternative way to create an array. This practice is
however discouraged because if $arr already contains
some value (e.g. string from request variable) then this
value will stay in the place and []
may actually stand
for string access
operator. It is always better to initialize a variable by a direct
assignment.
Note: As of PHP 7.1.0, applying the empty index operator on a string throws a fatal error. Formerly, the string was silently converted to an array.
Note: As of PHP 8.1.0, creating a new array from
false
value is deprecated. Creating a new array fromnull
and undefined values is still allowed.
To change a certain value, assign a new value to that element using its key. To remove a key/value pair, call the unset() function on it.
<?php
$arr = array(5 => 1, 12 => 2);
$arr[] = 56; // This is the same as $arr[13] = 56;
// at this point of the script
$arr["x"] = 42; // This adds a new element to
// the array with key "x"
unset($arr[5]); // This removes the element from the array
unset($arr); // This deletes the whole array
?>
Note:
As mentioned above, if no key is specified, the maximum of the existing int indices is taken, and the new key will be that maximum value plus 1 (but at least 0). If no int indices exist yet, the key will be
0
(zero).Note that the maximum integer key used for this need not currently exist in the array. It need only have existed in the array at some time since the last time the array was re-indexed. The following example illustrates:
<?php
// Create a simple array.
$array = array(1, 2, 3, 4, 5);
print_r($array);
// Now delete every item, but leave the array itself intact:
foreach ($array as $i => $value) {
unset($array[$i]);
}
print_r($array);
// Append an item (note that the new key is 5, instead of 0).
$array[] = 6;
print_r($array);
// Re-index:
$array = array_values($array);
$array[] = 7;
print_r($array);
?>The above example will output:
Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) Array ( ) Array ( [5] => 6 ) Array ( [0] => 6 [1] => 7 )
Array destructuring ¶
Arrays can be destructured using the []
(as of PHP 7.1.0) or
list() language constructs. These
constructs can be used to destructure an array into distinct variables.
<?php
$source_array = ['foo', 'bar', 'baz'];
[$foo, $bar, $baz] = $source_array;
echo $foo; // prints "foo"
echo $bar; // prints "bar"
echo $baz; // prints "baz"
?>
Array destructuring can be used in foreach to destructure a multi-dimensional array while iterating over it.
<?php
$source_array = [
[1, 'John'],
[2, 'Jane'],
];
foreach ($source_array as [$id, $name]) {
// logic here with $id and $name
}
?>
Array elements will be ignored if the variable is not provided. Array
destructuring always starts at index 0
.
<?php
$source_array = ['foo', 'bar', 'baz'];
// Assign the element at index 2 to the variable $baz
[, , $baz] = $source_array;
echo $baz; // prints "baz"
?>
As of PHP 7.1.0, associative arrays can be destructured too. This also allows for easier selection of the right element in numerically indexed arrays as the index can be explicitly specified.
<?php
$source_array = ['foo' => 1, 'bar' => 2, 'baz' => 3];
// Assign the element at index 'baz' to the variable $three
['baz' => $three] = $source_array;
echo $three; // prints 3
$source_array = ['foo', 'bar', 'baz'];
// Assign the element at index 2 to the variable $baz
[2 => $baz] = $source_array;
echo $baz; // prints "baz"
?>
Array destructuring can be used for easy swapping of two variables.
<?php
$a = 1;
$b = 2;
[$b, $a] = [$a, $b];
echo $a; // prints 2
echo $b; // prints 1
?>
Note:
The spread operator (
...
) is not supported in assignments.
Note:
Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an
E_NOTICE
-level error message (E_WARNING
-level as of PHP 8.0.0) will be issued, and the result will benull
.
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