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value='zh/language.types.array.php'>Chinese (Simplified)</option> <option value='help-translate.php'>Other</option> </select> </fieldset> </form> </div> </div><div id="language.types.array" class="sect1"> <h2 class="title">Arrays</h2> An <a href="language.types.array.php" class="type array">array</a> in PHP is actually an ordered map. A map is a type that associates values to keys. This type is optimized for several different uses; it can be treated as an array, list (vector), hash table (an implementation of a map), dictionary, collection, stack, queue, and probably more. As <a href="language.types.array.php" class="type array">array</a> values can be other <a href="language.types.array.php" class="type array">array</a>s, trees and multidimensional <a href="language.types.array.php" class="type array">array</a>s are also possible. Explanation of those data structures is beyond the scope of this manual, but at least one example is provided for each of them. For more information, look towards the considerable literature that exists about this broad topic. <div class="sect2" id="language.types.array.syntax"> <h3 class="title">Syntax</h3> <div class="sect3" id="language.types.array.syntax.array-func"> <h4 class="title">Specifying with <a href="function.array.php" class="function">array()</a></h4> An <a href="language.types.array.php" class="type array">array</a> can be created using the <a href="function.array.php" class="function">array()</a> language construct. It takes any number of comma-separated <code class="literal">key => value</code> pairs as arguments. <pre class="synopsis"> array( key => value, key2 => value2, key3 => value3, ... )</pre> The comma after the last array element is optional and can be omitted. This is usually done for single-line arrays, i.e. <code class="literal">array(1, 2)</code> is preferred over <code class="literal">array(1, 2, )</code>. 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. <blockquote class="note">Note: A short array syntax exists which replaces <code class="literal">array()</code> with <code class="literal">[]</code>. </blockquote> <div class="example" id="example-58"> Example #1 A simple array <div class="example-contents"> <div class="phpcode"><code><?php $array = array( "foo" => "bar", "bar" => "foo", ); // Using the short array syntax $array = [ "foo" => "bar", "bar" => "foo", ]; ?></code></div> </div> </div> The key can either be an <a href="language.types.integer.php" class="type int">int</a> or a <a href="language.types.string.php" class="type string">string</a>. The value can be of any type. Additionally the following key casts will occur: <ul class="itemizedlist"> <li class="listitem"> <a href="language.types.string.php" class="type String">String</a>s containing valid decimal <a href="language.types.integer.php" class="type int">int</a>s, unless the number is preceded by a <code class="literal">+</code> sign, will be cast to the <a href="language.types.integer.php" class="type int">int</a> type. E.g. the key <code class="literal">"8"</code> will actually be stored under <code class="literal">8</code>. On the other hand <code class="literal">"08"</code> will not be cast, as it isn't a valid decimal integer. </li> <li class="listitem"> <a href="language.types.float.php" class="type Float">Float</a>s are also cast to <a href="language.types.integer.php" class="type int">int</a>s, which means that the fractional part will be truncated. E.g. the key <code class="literal">8.7</code> will actually be stored under <code class="literal">8</code>. </li> <li class="listitem"> <a href="language.types.boolean.php" class="type Bool">Bool</a>s are cast to <a href="language.types.integer.php" class="type int">int</a>s, too, i.e. the key <code><a href="reserved.constants.php#constant.true">true</a></code> will actually be stored under <code class="literal">1</code> and the key <code><a href="reserved.constants.php#constant.false">false</a></code> under <code class="literal">0</code>. </li> <li class="listitem"> <a href="language.types.null.php" class="type Null">Null</a> will be cast to the empty string, i.e. the key <code class="literal">null</code> will actually be stored under <code class="literal">""</code>. </li> <li class="listitem"> <a href="language.types.array.php" class="type Array">Array</a>s and <a href="language.types.object.php" class="type object">object</a>s can not be used as keys. Doing so will result in a warning: <code class="literal">Illegal offset type</code>. </li> </ul> If multiple elements in the array declaration use the same key, only the last one will be used as all others are overwritten. <div class="example" id="example-59"> Example #2 Type Casting and Overwriting example <div class="example-contents"> <div class="phpcode"><code><?php $array = array( 1 => "a", "1" => "b", 1.5 => "c", true => "d", ); var_dump($array); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> array(1) { [1]=> string(1) "d" } </pre></div> </div> <div class="example-contents"> As all the keys in the above example are cast to <code class="literal">1</code>, the value will be overwritten on every new element and the last assigned value <code class="literal">"d"</code> is the only one left over. </div> </div> PHP arrays can contain <a href="language.types.integer.php" class="type int">int</a> and <a href="language.types.string.php" class="type string">string</a> keys at the same time as PHP does not distinguish between indexed and associative arrays. <div class="example" id="example-60"> Example #3 Mixed <a href="language.types.integer.php" class="type int">int</a> and <a href="language.types.string.php" class="type string">string</a> keys <div class="example-contents"> <div class="phpcode"><code><?php $array = array( "foo" => "bar", "bar" => "foo", 100 => -100, -100 => 100, ); var_dump($array); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> array(4) { ["foo"]=> string(3) "bar" ["bar"]=> string(3) "foo" [100]=> int(-100) [-100]=> int(100) } </pre></div> </div> </div> The key is optional. If it is not specified, PHP will use the increment of the largest previously used <a href="language.types.integer.php" class="type int">int</a> key. <div class="example" id="example-61"> Example #4 Indexed arrays without key <div class="example-contents"> <div class="phpcode"><code><?php $array = array("foo", "bar", "hello", "world"); var_dump($array); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> array(4) { [0]=> string(3) "foo" [1]=> string(3) "bar" [2]=> string(5) "hello" [3]=> string(5) "world" } </pre></div> </div> </div> It is possible to specify the key only for some elements and leave it out for others: <div class="example" id="example-62"> Example #5 Keys not on all elements <div class="example-contents"> <div class="phpcode"><code><?php $array = array( "a", "b", 6 => "c", "d", ); var_dump($array); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> array(4) { [0]=> string(1) "a" [1]=> string(1) "b" [6]=> string(1) "c" [7]=> string(1) "d" } </pre></div> </div> <div class="example-contents"> As you can see the last value <code class="literal">"d"</code> was assigned the key <code class="literal">7</code>. This is because the largest integer key before that was <code class="literal">6</code>. </div> </div> <div class="example" id="example-63"> Example #6 Complex Type Casting and Overwriting example <div class="example-contents"> This example includes all variations of type casting of keys and overwriting of elements. </div> <div class="example-contents"> <div class="phpcode"><code><?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); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> 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" } </pre></div> </div> </div> <div class="example" id="example-64"> Example #7 Negative index example <div class="example-contents"> When assigning a negative integer key <code class="literal">n</code>, PHP will take care to assign the next key to <code class="literal">n+1</code>. </div> <div class="example-contents"> <div class="phpcode"><code><?php $array = []; $array[-5] = 1; $array[] = 2; var_dump($array); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> array(2) { [-5]=> int(1) [-4]=> int(2) } </pre></div> </div> <div class="warning">Warning Prior to PHP 8.3.0, assigning a negative integer key <code class="literal">n</code> would assign the next key to <code class="literal">0</code>, the previous example would therefore output: <div class="informalexample"> <div class="example-contents screen"> <div class="cdata"><pre> array(2) { [-5]=> int(1) [0]=> int(2) } </pre></div> </div> </div> </div> </div> </div> <div class="sect3" id="language.types.array.syntax.accessing"> <h4 class="title">Accessing array elements with square bracket syntax</h4> Array elements can be accessed using the <code class="literal">array[key]</code> syntax. <div class="example" id="example-65"> Example #8 Accessing array elements <div class="example-contents"> <div class="phpcode"><code><?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"]); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> string(3) "bar" int(24) string(3) "foo" </pre></div> </div> </div> <blockquote class="note">Note: Prior to PHP 8.0.0, square brackets and curly braces could be used interchangeably for accessing array elements (e.g. <code class="literal">$array[42]</code> and <code class="literal">$array{42}</code> 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. </blockquote> <div class="example" id="example-66"> Example #9 Array dereferencing <div class="example-contents"> <div class="phpcode"><code><?php function getArray() { return array(1, 2, 3); } $secondElement = getArray()[1]; ?></code></div> </div> </div> <blockquote class="note">Note: Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an <code><a href="errorfunc.constants.php#constant.e-warning">E_WARNING</a></code>-level error message (<code><a href="errorfunc.constants.php#constant.e-notice">E_NOTICE</a></code>-level prior to PHP 8.0.0) will be issued, and the result will be <code><a href="reserved.constants.php#constant.null">null</a></code>. </blockquote> <blockquote class="note">Note: Array dereferencing a scalar value which is not a <a href="language.types.string.php" class="type string">string</a> yields <code><a href="reserved.constants.php#constant.null">null</a></code>. Prior to PHP 7.4.0, that did not issue an error message. As of PHP 7.4.0, this issues <code><a href="errorfunc.constants.php#constant.e-notice">E_NOTICE</a></code>; as of PHP 8.0.0, this issues <code><a href="errorfunc.constants.php#constant.e-warning">E_WARNING</a></code>. </blockquote> </div> <div class="sect3" id="language.types.array.syntax.modifying"> <h4 class="title">Creating/modifying with square bracket syntax</h4> An existing <a href="language.types.array.php" class="type array">array</a> can be modified by explicitly setting values in it. This is done by assigning values to the <a href="language.types.array.php" class="type array">array</a>, specifying the key in brackets. The key can also be omitted, resulting in an empty pair of brackets (<code class="literal">[]</code>). <pre class="synopsis"> $arr[key] = value; $arr[] = value; // key may be an <a href="language.types.integer.php" class="type int">int</a> or <a href="language.types.string.php" class="type string">string</a> // value may be any value of any type</pre> If <var class="varname">$arr</var> doesn't exist yet or is set to <code><a href="reserved.constants.php#constant.null">null</a></code> or <code><a href="reserved.constants.php#constant.false">false</a></code>, it will be created, so this is also an alternative way to create an <a href="language.types.array.php" class="type array">array</a>. This practice is however discouraged because if <var class="varname">$arr</var> already contains some value (e.g. <a href="language.types.string.php" class="type string">string</a> from request variable) then this value will stay in the place and <code class="literal">[]</code> may actually stand for <a href="language.types.string.php#language.types.string.substr" class="link">string access operator</a>. It is always better to initialize a variable by a direct assignment. <blockquote class="note">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. </blockquote> <blockquote class="note">Note: As of PHP 8.1.0, creating a new array from <code><a href="reserved.constants.php#constant.false">false</a></code> value is deprecated. Creating a new array from <code><a href="reserved.constants.php#constant.null">null</a></code> and undefined values is still allowed. </blockquote> To change a certain value, assign a new value to that element using its key. To remove a key/value pair, call the <a href="function.unset.php" class="function">unset()</a> function on it. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?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 ?></code></div> </div> </div> <blockquote class="note">Note: As mentioned above, if no key is specified, the maximum of the existing <a href="language.types.integer.php" class="type int">int</a> indices is taken, and the new key will be that maximum value plus 1 (but at least 0). If no <a href="language.types.integer.php" class="type int">int</a> indices exist yet, the key will be <code class="literal">0</code> (zero). Note that the maximum integer key used for this need not currently exist in the <a href="language.types.array.php" class="type array">array</a>. It need only have existed in the <a href="language.types.array.php" class="type array">array</a> at some time since the last time the <a href="language.types.array.php" class="type array">array</a> was re-indexed. The following example illustrates: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?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); ?></code></div> </div> The above example will output: <div class="example-contents screen"> <div class="cdata"><pre> Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) Array ( ) Array ( [5] => 6 ) Array ( [0] => 6 [1] => 7 ) </pre></div> </div> </div> </blockquote> </div> <div class="sect3" id="language.types.array.syntax.destructuring"> <h4 class="title">Array destructuring</h4> Arrays can be destructured using the <code class="literal">[]</code> (as of PHP 7.1.0) or <a href="function.list.php" class="function">list()</a> language constructs. These constructs can be used to destructure an array into distinct variables. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $source_array = ['foo', 'bar', 'baz']; [$foo, $bar, $baz] = $source_array; echo $foo; // prints "foo" echo $bar; // prints "bar" echo $baz; // prints "baz" ?></code></div> </div> </div> Array destructuring can be used in <a href="control-structures.foreach.php" class="link"><code class="literal">foreach</code></a> to destructure a multi-dimensional array while iterating over it. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $source_array = [ [1, 'John'], [2, 'Jane'], ]; foreach ($source_array as [$id, $name]) { // logic here with $id and $name } ?></code></div> </div> </div> Array elements will be ignored if the variable is not provided. Array destructuring always starts at index <code class="literal">0</code>. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $source_array = ['foo', 'bar', 'baz']; // Assign the element at index 2 to the variable $baz [, , $baz] = $source_array; echo $baz; // prints "baz" ?></code></div> </div> </div> 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. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?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" ?></code></div> </div> </div> Array destructuring can be used for easy swapping of two variables. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $a = 1; $b = 2; [$b, $a] = [$a, $b]; echo $a; // prints 2 echo $b; // prints 1 ?></code></div> </div> </div> <blockquote class="note">Note: The spread operator (<code class="literal">...</code>) is not supported in assignments. </blockquote> <blockquote class="note">Note: Attempting to access an array key which has not been defined is the same as accessing any other undefined variable: an <code><a href="errorfunc.constants.php#constant.e-warning">E_WARNING</a></code>-level error message (<code><a href="errorfunc.constants.php#constant.e-notice">E_NOTICE</a></code>-level prior to PHP 8.0.0) will be issued, and the result will be <code><a href="reserved.constants.php#constant.null">null</a></code>. </blockquote> </div> </div> <div class="sect2" id="language.types.array.useful-funcs"> <h3 class="title">Useful functions</h3> There are quite a few useful functions for working with arrays. See the <a href="ref.array.php" class="link">array functions</a> section. <blockquote class="note">Note: The <a href="function.unset.php" class="function">unset()</a> function allows removing keys from an <a href="language.types.array.php" class="type array">array</a>. Be aware that the array will not be reindexed. If a true "remove and shift" behavior is desired, the <a href="language.types.array.php" class="type array">array</a> can be reindexed using the <a href="function.array-values.php" class="function">array_values()</a> function. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $a = array(1 => 'one', 2 => 'two', 3 => 'three'); unset($a[2]); /* will produce an array that would have been defined as $a = array(1 => 'one', 3 => 'three'); and NOT $a = array(1 => 'one', 2 =>'three'); */ $b = array_values($a); // Now $b is array(0 => 'one', 1 =>'three') ?></code></div> </div> </div> </blockquote> The <a href="control-structures.foreach.php" class="link"><code class="literal">foreach</code></a> control structure exists specifically for <a href="language.types.array.php" class="type array">array</a>s. It provides an easy way to traverse an <a href="language.types.array.php" class="type array">array</a>. </div> <div class="sect2" id="language.types.array.donts"> <h3 class="title">Array do's and don'ts</h3> <div class="sect3" id="language.types.array.foo-bar"> <h4 class="title">Why is <code class="literal">$foo[bar]</code> wrong?</h4> Always use quotes around a string literal array index. For example, <code class="literal">$foo['bar']</code> is correct, while <code class="literal">$foo[bar]</code> is not. But why? It is common to encounter this kind of syntax in old scripts: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $foo[bar] = 'enemy'; echo $foo[bar]; // etc ?></code></div> </div> </div> This is wrong, but it works. The reason is that this code has an undefined constant (<code class="literal">bar</code>) rather than a <a href="language.types.string.php" class="type string">string</a> (<code class="literal">'bar'</code> - notice the quotes). It works because PHP automatically converts a bare string (an unquoted <a href="language.types.string.php" class="type string">string</a> which does not correspond to any known symbol) into a <a href="language.types.string.php" class="type string">string</a> which contains the bare <a href="language.types.string.php" class="type string">string</a>. For instance, if there is no defined constant named <code>bar</code>, then PHP will substitute in the <a href="language.types.string.php" class="type string">string</a> <code class="literal">'bar'</code> and use that. <div class="warning">Warning The fallback to treat an undefined constant as bare string issues an error of level <code><a href="errorfunc.constants.php#constant.e-notice">E_NOTICE</a></code>. This has been deprecated as of PHP 7.2.0, and issues an error of level <code><a href="errorfunc.constants.php#constant.e-warning">E_WARNING</a></code>. As of PHP 8.0.0, it has been removed and throws an <a href="class.error.php" class="classname">Error</a> exception. </div> <blockquote class="note">Note: This does not mean to always quote the key. Do not quote keys which are <a href="language.constants.php" class="link">constants</a> or <a href="language.variables.php" class="link">variables</a>, as this will prevent PHP from interpreting them. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php error_reporting(E_ALL); ini_set('display_errors', true); ini_set('html_errors', false); // Simple array: $array = array(1, 2); $count = count($array); for ($i = 0; $i < $count; $i++) { echo "\nChecking $i: \n"; echo "Bad: " . $array['$i'] . "\n"; echo "Good: " . $array[$i] . "\n"; echo "Bad: {$array['$i']}\n"; echo "Good: {$array[$i]}\n"; } ?></code></div> </div> </div> The above example will output: <div class="example-contents screen"> <div class="cdata"><pre> Checking 0: Notice: Undefined index: $i in /path/to/script.html on line 9 Bad: Good: 1 Notice: Undefined index: $i in /path/to/script.html on line 11 Bad: Good: 1 Checking 1: Notice: Undefined index: $i in /path/to/script.html on line 9 Bad: Good: 2 Notice: Undefined index: $i in /path/to/script.html on line 11 Bad: Good: 2 </pre></div> </div> </blockquote> More examples to demonstrate this behaviour: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php // Show all errors error_reporting(E_ALL); $arr = array('fruit' => 'apple', 'veggie' => 'carrot'); // Correct print $arr['fruit']; // apple print $arr['veggie']; // carrot // Incorrect. This works but also throws a PHP error of level E_NOTICE because // of an undefined constant named fruit // // Notice: Use of undefined constant fruit - assumed 'fruit' in... print $arr[fruit]; // apple // This defines a constant to demonstrate what's going on. The value 'veggie' // is assigned to a constant named fruit. define('fruit', 'veggie'); // Notice the difference now print $arr['fruit']; // apple print $arr[fruit]; // carrot // The following is okay, as it's inside a string. Constants are not looked for // within strings, so no E_NOTICE occurs here print "Hello $arr[fruit]"; // Hello apple // With one exception: braces surrounding arrays within strings allows constants // to be interpreted print "Hello {$arr[fruit]}"; // Hello carrot print "Hello {$arr['fruit']}"; // Hello apple // Concatenation is another option print "Hello " . $arr['fruit']; // Hello apple ?></code></div> </div> </div> <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code>// This will not work, and will result in a parse error, such as: // Parse error: parse error, expecting T_STRING' or T_VARIABLE' or T_NUM_STRING' // This of course applies to using superglobals in strings as well print "Hello $arr['fruit']"; print "Hello $_GET['foo']";</code></div> </div> </div> When <a href="errorfunc.configuration.php#ini.error-reporting" class="link">error_reporting</a> is set to show <code><a href="errorfunc.constants.php#constant.e-notice">E_NOTICE</a></code> level errors (by setting it to <code><a href="errorfunc.constants.php#constant.e-all">E_ALL</a></code>, for example), such uses will become immediately visible. By default, <a href="errorfunc.configuration.php#ini.error-reporting" class="link">error_reporting</a> is set not to show notices. As stated in the <a href="language.types.array.php#language.types.array.syntax" class="link">syntax</a> section, what's inside the square brackets ('<code class="literal">[</code>' and '<code class="literal">]</code>') must be an expression. This means that code like this works: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php echo $arr[somefunc($bar)]; ?></code></div> </div> </div> This is an example of using a function return value as the array index. PHP also knows about constants: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $error_descriptions[E_ERROR] = "A fatal error has occurred"; $error_descriptions[E_WARNING] = "PHP issued a warning"; $error_descriptions[E_NOTICE] = "This is just an informal notice"; ?></code></div> </div> </div> Note that <code><a href="errorfunc.constants.php#constant.e-error">E_ERROR</a></code> is also a valid identifier, just like <code class="literal">bar</code> in the first example. But the last example is in fact the same as writing: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $error_descriptions[1] = "A fatal error has occurred"; $error_descriptions[2] = "PHP issued a warning"; $error_descriptions[8] = "This is just an informal notice"; ?></code></div> </div> </div> because <code><a href="errorfunc.constants.php#constant.e-error">E_ERROR</a></code> equals <code class="literal">1</code>, etc. <div class="sect4" id="language.types.array.foo-bar.why"> <h5 class="title">So why is it bad then?</h5> At some point in the future, the PHP team might want to add another constant or keyword, or a constant in other code may interfere. For example, it is already wrong to use the words <code class="literal">empty</code> and <code class="literal">default</code> this way, since they are <a href="reserved.php" class="link">reserved keywords</a>. <blockquote class="note">Note: To reiterate, inside a double-quoted <a href="language.types.string.php" class="type string">string</a>, it's valid to not surround array indexes with quotes so <code class="literal">"$foo[bar]"</code> is valid. See the above examples for details on why as well as the section on <a href="language.types.string.php#language.types.string.parsing" class="link">variable parsing in strings</a>. </blockquote> </div> </div> </div> <div class="sect2" id="language.types.array.casting"> <h3 class="title">Converting to array</h3> For any of the types <a href="language.types.integer.php" class="type int">int</a>, <a href="language.types.float.php" class="type float">float</a>, <a href="language.types.string.php" class="type string">string</a>, <a href="language.types.boolean.php" class="type bool">bool</a> and <a href="language.types.resource.php" class="type resource">resource</a>, converting a value to an <a href="language.types.array.php" class="type array">array</a> results in an array with a single element with index zero and the value of the scalar which was converted. In other words, <code class="code">(array) $scalarValue</code> is exactly the same as <code class="literal">array($scalarValue)</code>. If an <a href="language.types.object.php" class="type object">object</a> is converted to an <a href="language.types.array.php" class="type array">array</a>, the result is an <a href="language.types.array.php" class="type array">array</a> whose elements are the <a href="language.types.object.php" class="type object">object</a>'s properties. The keys are the member variable names, with a few notable exceptions: integer properties are unaccessible; private variables have the class name prepended to the variable name; protected variables have a '*' prepended to the variable name. These prepended values have <code class="literal">NUL</code> bytes on either side. Uninitialized <a href="language.oop5.properties.php#language.oop5.properties.typed-properties" class="link">typed properties</a> are silently discarded. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php class A { private $B; protected $C; public $D; function __construct() { $this->{1} = null; } } var_export((array) new A()); ?></code></div> </div> The above example will output: <div class="example-contents screen"> <div class="cdata"><pre> array ( '' . "\0" . 'A' . "\0" . 'B' => NULL, '' . "\0" . '*' . "\0" . 'C' => NULL, 'D' => NULL, 1 => NULL, ) </pre></div> </div> </div> These <code class="literal">NUL</code> can result in some unexpected behaviour: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php class A { private $A; // This will become '\0A\0A' } class B extends A { private $A; // This will become '\0B\0A' public $AA; // This will become 'AA' } var_dump((array) new B()); ?></code></div> </div> The above example will output: <div class="example-contents screen"> <div class="cdata"><pre> array(3) { ["BA"]=> NULL ["AA"]=> NULL ["AA"]=> NULL } </pre></div> </div> </div> The above will appear to have two keys named 'AA', although one of them is actually named '\0A\0A'. Converting <code><a href="reserved.constants.php#constant.null">null</a></code> to an <a href="language.types.array.php" class="type array">array</a> results in an empty <a href="language.types.array.php" class="type array">array</a>. </div> <div class="sect2" id="language.types.array.comparing"> <h3 class="title">Comparing</h3> It is possible to compare arrays with the <a href="function.array-diff.php" class="function">array_diff()</a> function and with <a href="language.operators.array.php" class="link">array operators</a>. </div> <div class="sect2" id="language.types.array.unpacking"> <h3 class="title">Array unpacking</h3> An array prefixed by <code class="code">...</code> will be expanded in place during array definition. Only arrays and objects which implement <a href="class.traversable.php" class="interfacename">Traversable</a> can be expanded. Array unpacking with <code class="code">...</code> is available as of PHP 7.4.0. It's possible to expand multiple times, and add normal elements before or after the <code class="code">...</code> operator: <div class="example" id="example-67"> Example #10 Simple array unpacking <div class="example-contents"> <div class="phpcode"><code><?php // Using short array syntax. // Also, works with array() syntax. $arr1 = [1, 2, 3]; $arr2 = [...$arr1]; //[1, 2, 3] $arr3 = [0, ...$arr1]; //[0, 1, 2, 3] $arr4 = [...$arr1, ...$arr2, 111]; //[1, 2, 3, 1, 2, 3, 111] $arr5 = [...$arr1, ...$arr1]; //[1, 2, 3, 1, 2, 3] function getArr() { return ['a', 'b']; } $arr6 = [...getArr(), 'c' => 'd']; //['a', 'b', 'c' => 'd'] ?></code></div> </div> </div> Unpacking an array with the <code class="code">...</code> operator follows the semantics of the <a href="function.array-merge.php" class="function">array_merge()</a> function. That is, later string keys overwrite earlier ones and integer keys are renumbered: <div class="example" id="example-68"> Example #11 Array unpacking with duplicate key <div class="example-contents"> <div class="phpcode"><code><?php // string key $arr1 = ["a" => 1]; $arr2 = ["a" => 2]; $arr3 = ["a" => 0, ...$arr1, ...$arr2]; var_dump($arr3); // ["a" => 2] // integer key $arr4 = [1, 2, 3]; $arr5 = [4, 5, 6]; $arr6 = [...$arr4, ...$arr5]; var_dump($arr6); // [1, 2, 3, 4, 5, 6] // Which is [0 => 1, 1 => 2, 2 => 3, 3 => 4, 4 => 5, 5 => 6] // where the original integer keys have not been retained. ?></code></div> </div> </div> <blockquote class="note">Note: Keys that are neither integers nor strings throw a <a href="class.typeerror.php" class="classname">TypeError</a>. Such keys can only be generated by a <a href="class.traversable.php" class="interfacename">Traversable</a> object. </blockquote> <blockquote class="note">Note: Prior to PHP 8.1, unpacking an array which has a string key is not supported: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $arr1 = [1, 2, 3]; $arr2 = ['a' => 4]; $arr3 = [...$arr1, ...$arr2]; // Fatal error: Uncaught Error: Cannot unpack array with string keys in example.php:5 $arr4 = [1, 2, 3]; $arr5 = [4, 5]; $arr6 = [...$arr4, ...$arr5]; // works. [1, 2, 3, 4, 5] ?></code></div> </div> </div> </blockquote> </div> <div class="sect2" id="language.types.array.examples"> <h3 class="title">Examples</h3> The array type in PHP is very versatile. Here are some examples: <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php // This: $a = array( 'color' => 'red', 'taste' => 'sweet', 'shape' => 'round', 'name' => 'apple', 4 // key will be 0 ); $b = array('a', 'b', 'c'); // . . .is completely equivalent with this: $a = array(); $a['color'] = 'red'; $a['taste'] = 'sweet'; $a['shape'] = 'round'; $a['name'] = 'apple'; $a[] = 4; // key will be 0 $b = array(); $b[] = 'a'; $b[] = 'b'; $b[] = 'c'; // After the above code is executed, $a will be the array // array('color' => 'red', 'taste' => 'sweet', 'shape' => 'round', // 'name' => 'apple', 0 => 4), and $b will be the array // array(0 => 'a', 1 => 'b', 2 => 'c'), or simply array('a', 'b', 'c'). ?></code></div> </div> </div> <div class="example" id="example-69"> Example #12 Using array() <div class="example-contents"> <div class="phpcode"><code><?php // Array as (property-)map $map = array( 'version' => 4, 'OS' => 'Linux', 'lang' => 'english', 'short_tags' => true ); // strictly numerical keys $array = array( 7, 8, 0, 156, -10 ); // this is the same as array(0 => 7, 1 => 8, ...) $switching = array( 10, // key = 0 5 => 6, 3 => 7, 'a' => 4, 11, // key = 6 (maximum of integer-indices was 5) '8' => 2, // key = 8 (integer!) '02' => 77, // key = '02' 0 => 12 // the value 10 will be overwritten by 12 ); // empty array $empty = array(); ?></code></div> </div> </div> <div class="example" id="language.types.array.examples.loop"> Example #13 Collection <div class="example-contents"> <div class="phpcode"><code><?php $colors = array('red', 'blue', 'green', 'yellow'); foreach ($colors as $color) { echo "Do you like $color?\n"; } ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> Do you like red? Do you like blue? Do you like green? Do you like yellow? </pre></div> </div> </div> Changing the values of the <a href="language.types.array.php" class="type array">array</a> directly is possible by passing them by reference. <div class="example" id="language.types.array.examples.changeloop"> Example #14 Changing element in the loop <div class="example-contents"> <div class="phpcode"><code><?php foreach ($colors as &$color) { $color = mb_strtoupper($color); } unset($color); /* ensure that following writes to $color will not modify the last array element */ print_r($colors); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> Array ( [0] => RED [1] => BLUE [2] => GREEN [3] => YELLOW ) </pre></div> </div> </div> This example creates a one-based array. <div class="example" id="example-72"> Example #15 One-based index <div class="example-contents"> <div class="phpcode"><code><?php $firstquarter = array(1 => 'January', 'February', 'March'); print_r($firstquarter); ?></code></div> </div> <div class="example-contents">The above example will output:</div> <div class="example-contents screen"> <div class="cdata"><pre> Array ( [1] => 'January' [2] => 'February' [3] => 'March' ) </pre></div> </div> </div> <div class="example" id="example-73"> Example #16 Filling an array <div class="example-contents"> <div class="phpcode"><code><?php // fill an array with all items from a directory $handle = opendir('.'); while (false !== ($file = readdir($handle))) { $files[] = $file; } closedir($handle); ?></code></div> </div> </div> <a href="language.types.array.php" class="type Array">Array</a>s are ordered. The order can be changed using various sorting functions. See the <a href="ref.array.php" class="link">array functions</a> section for more information. The <a href="function.count.php" class="function">count()</a> function can be used to count the number of items in an <a href="language.types.array.php" class="type array">array</a>. <div class="example" id="example-74"> Example #17 Sorting an array <div class="example-contents"> <div class="phpcode"><code><?php sort($files); print_r($files); ?></code></div> </div> </div> Because the value of an <a href="language.types.array.php" class="type array">array</a> can be anything, it can also be another <a href="language.types.array.php" class="type array">array</a>. This enables the creation of recursive and multi-dimensional <a href="language.types.array.php" class="type array">array</a>s. <div class="example" id="example-75"> Example #18 Recursive and multi-dimensional arrays <div class="example-contents"> <div class="phpcode"><code><?php $fruits = array ( "fruits" => array ( "a" => "orange", "b" => "banana", "c" => "apple" ), "numbers" => array ( 1, 2, 3, 4, 5, 6 ), "holes" => array ( "first", 5 => "second", "third" ) ); // Some examples to address values in the array above echo $fruits["holes"][5]; // prints "second" echo $fruits["fruits"]["a"]; // prints "orange" unset($fruits["holes"][0]); // remove "first" // Create a new multi-dimensional array $juices["apple"]["green"] = "good"; ?></code></div> </div> </div> <a href="language.types.array.php" class="type Array">Array</a> assignment always involves value copying. Use the <a href="language.operators.php" class="link">reference operator</a> to copy an <a href="language.types.array.php" class="type array">array</a> by reference. <div class="informalexample"> <div class="example-contents"> <div class="phpcode"><code><?php $arr1 = array(2, 3); $arr2 = $arr1; $arr2[] = 4; // $arr2 is changed, // $arr1 is still array(2, 3) $arr3 = &$arr1; $arr3[] = 4; // now $arr1 and $arr3 are the same ?></code></div> </div> </div> </div> </div> <div class="contribute"> <h3 class="title">Found A Problem?</h3> <div> </div> <div class="edit-bug"> <a href="https://github.com/php/doc-base/blob/master/README.md" title="This will take you to our contribution guidelines on GitHub" target="_blank" rel="noopener noreferrer">Learn How To Improve This Page</a> • <a href="https://github.com/php/doc-en/blob/master/language/types/array.xml">Submit a Pull Request</a> • <a href="https://github.com/php/doc-en/issues/new?body=From%20manual%20page:%20https:%2F%2Fphp.net%2Flanguage.types.array%0A%0A---">Report a Bug</a> </div> </div><section id="usernotes"> <div class="head"> <a href="/manual/add-note.php?sect=language.types.array&repo=en&redirect=https://www.php.net/manual/en/language.types.array.php">＋add a note</a> <h3 class="title">User Contributed Notes 5 notes</h3> </div><div id="allnotes"> <div class="note" id="104064"> <div class="votes"> <div id="Vu104064"> <a href="/manual/vote-note.php?id=104064&page=language.types.array&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd104064"> <a href="/manual/vote-note.php?id=104064&page=language.types.array&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V104064" title="55% like this..."> 128 </div> </div> <a href="#104064" class="name"> mlvljr</a><a class="genanchor" href="#104064"> ¶</a><div class="date" title="2011-05-20 06:37">13 years ago</div> <div class="text" id="Hcom104064"> <div class="phpcode"><code>please note that when arrays are copied, the "reference status" of their members is preserved (<a href="http://www.php.net/manual/en/language.references.whatdo.php" rel="nofollow" target="_blank">http://www.php.net/manual/en/language.references.whatdo.php</a>).</code></div> </div> </div> <div class="note" id="118855"> <div class="votes"> <div id="Vu118855"> <a href="/manual/vote-note.php?id=118855&page=language.types.array&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd118855"> <a href="/manual/vote-note.php?id=118855&page=language.types.array&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V118855" title="58% like this..."> 74 </div> </div> <a href="#118855" class="name"> thomas tulinsky</a><a class="genanchor" href="#118855"> ¶</a><div class="date" title="2016-02-17 08:10">9 years ago</div> <div class="text" id="Hcom118855"> <div class="phpcode"><code>I think your first, main example is needlessly confusing, very confusing to newbies: $array = array( "foo" => "bar", "bar" => "foo", ); It should be removed. For newbies: An array index can be any string value, even a value that is also a value in the array. The value of array["foo"] is "bar". The value of array["bar"] is "foo" The following expressions are both true: $array["foo"] == "bar" $array["bar"] == "foo"</code></div> </div> </div> <div class="note" id="80311"> <div class="votes"> <div id="Vu80311"> <a href="/manual/vote-note.php?id=80311&page=language.types.array&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd80311"> <a href="/manual/vote-note.php?id=80311&page=language.types.array&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V80311" title="52% like this..."> 59 </div> </div> <a href="#80311" class="name"> ken underscore yap atsign email dot com</a><a class="genanchor" href="#80311"> ¶</a><div class="date" title="2008-01-09 08:00">17 years ago</div> <div class="text" id="Hcom80311"> <div class="phpcode"><code>"If you convert a NULL value to an array, you get an empty array." This turns out to be a useful property. Say you have a search function that returns an array of values on success or NULL if nothing found. <?php $values = search(...); ?> Now you want to merge the array with another array. What do we do if $values is NULL? No problem: <?php $combined = array_merge((array)$values, $other); ?> Voila.</code></div> </div> </div> <div class="note" id="52124"> <div class="votes"> <div id="Vu52124"> <a href="/manual/vote-note.php?id=52124&page=language.types.array&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd52124"> <a href="/manual/vote-note.php?id=52124&page=language.types.array&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V52124" title="52% like this..."> 55 </div> </div> <a href="#52124" class="name"> jeff splat codedread splot com</a><a class="genanchor" href="#52124"> ¶</a><div class="date" title="2005-04-21 09:16">19 years ago</div> <div class="text" id="Hcom52124"> <div class="phpcode"><code>Beware that if you're using strings as indices in the $_POST array, that periods are transformed into underscores: <html> <body> <?php printf("POST: "); print_r($_POST); printf(" "); ?> <form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>"> <input type="hidden" name="Windows3.1" value="Sux"> <input type="submit" value="Click" /> </form> </body> </html> Once you click on the button, the page displays the following: POST: Array ( [Windows3_1] => Sux )</code></div> </div> </div> <div class="note" id="112289"> <div class="votes"> <div id="Vu112289"> <a href="/manual/vote-note.php?id=112289&page=language.types.array&vote=up" title="Vote up!" class="usernotes-voteu">up</a> </div> <div id="Vd112289"> <a href="/manual/vote-note.php?id=112289&page=language.types.array&vote=down" title="Vote down!" class="usernotes-voted">down</a> </div> <div class="tally" id="V112289" title="52% like this..."> 37 </div> </div> <a href="#112289" class="name"> chris at ocportal dot com</a><a class="genanchor" href="#112289"> ¶</a><div class="date" title="2013-05-28 09:01">11 years ago</div> <div class="text" id="Hcom112289"> <div class="phpcode"><code>Note that array value buckets are reference-safe, even through serialization. <?php $x='initial'; $test=array('A'=>&$x,'B'=>&$x); $test=unserialize(serialize($test)); $test['A']='changed'; echo $test['B']; // Outputs "changed" ?> This can be useful in some cases, for example saving RAM within complex structures.</code></div> </div> </div></div> <div class="foot"><a href="/manual/add-note.php?sect=language.types.array&repo=en&redirect=https://www.php.net/manual/en/language.types.array.php">＋add a note</a></div> </section> </section> <aside class='layout-menu'> <ul class='parent-menu-list'> <li> <a href="language.types.php">Types</a> <ul class='child-menu-list'> <li class=""> <a href="language.types.intro.php" title="Introduction">Introduction</a> </li> <li class=""> <a href="language.types.type-system.php" title="Type System">Type System</a> </li> <li class=""> <a href="language.types.null.php" title="NULL">NULL</a> </li> <li class=""> <a href="language.types.boolean.php" title="Booleans">Booleans</a> </li> <li class=""> <a 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