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本文档使用 PHP中文网手册 发布
PHP 中的 数组 实际上是一个有序映射。映射是一种把 values 关联到 keys 的类型。此类型在很多方面做了优化,因此可以把它当成真正的数组,或列表(向量),散列表(是映射的一种实现),字典,集合,栈,队列以及更多可能性。由于数组元素的值也可以是另一个数组,树形结构和多维数组也是允许的。
解释这些结构超出了本手册的范围,但对于每种结构至少会提供一个例子。要得到这些结构的更多信息,建议参考有关此广阔主题的其它著作。
可以用 array() 语言结构来新建一个数组。它接受任意数量用逗号分隔的 键(key) => 值(value) 对。
array( key => value , ... ) // 键(key)可是是一个整数 integer 或字符串 string // 值(value)可以是任意类型的值
最后一个数组单元之后的逗号可以省略。通常用于单行数组定义中,例如常用 array(1, 2) 而不是 array(1, 2, )。对多行数组定义通常保留最后一个逗号,这样要添加一个新单元时更方便。
自 5.4 起可以使用短数组定义语法,用 [] 替代 array()。
Example #1 一个简单数组
<?php
$array = array(
"foo" => "bar" ,
"bar" => "foo" ,
);
// 自 PHP 5.4 起
$array = [
"foo" => "bar" ,
"bar" => "foo" ,
];
?>
key 可以是 integer 或者 string 。value 可以是任意类型。
此外 key 会有如下的强制转换:
如果在数组定义中多个单元都使用了同一个键名,则只使用了最后一个,之前的都被覆盖了。
Example #2 类型强制与覆盖示例
<?php
$array = array(
1 => "a" ,
"1" => "b" ,
1.5 => "c" ,
true => "d" ,
);
var_dump ( $array );
?>
以上例程会输出:
array(1) { [1]=> string(1) "d" }
上例中所有的键名都被强制转换为 1,则每一个新单元都会覆盖前一个的值,最后剩下的只有一个 "d"。
PHP 数组可以同时含有 integer 和 string 类型的键名,因为 PHP 实际并不区分索引数组和关联数组。
如果对给出的值没有指定键名,则取当前最大的整数索引值,而新的键名将是该值加一。如果指定的键名已经有了值,则该值会被覆盖。
Example #3 混合 integer 和 string 键名
<?php
$array = array(
"foo" => "bar" ,
"bar" => "foo" ,
100 => - 100 ,
- 100 => 100 ,
);
var_dump ( $array );
?>
以上例程会输出:
array(4) { ["foo"]=> string(3) "bar" ["bar"]=> string(3) "foo" [100]=> int(-100) [-100]=> int(100) }
key 为可选项。如果未指定,PHP 将自动使用之前用过的最大 integer 键名加上 1 作为新的键名。
Example #4 没有键名的索引数组
<?php
$array = array( "foo" , "bar" , "hallo" , "world" );
var_dump ( $array );
?>
以上例程会输出:
array(4) { [0]=> string(3) "foo" [1]=> string(3) "bar" [2]=> string(5) "hallo" [3]=> string(5) "world" }
还可以只对某些单元指定键名而对其它的空置:
Example #5 仅对部分单元指定键名
<?php
$array = array(
"a" ,
"b" ,
6 => "c" ,
"d" ,
);
var_dump ( $array );
?>
以上例程会输出:
array(4) { [0]=> string(1) "a" [1]=> string(1) "b" [6]=> string(1) "c" [7]=> string(1) "d" }
可以看到最后一个值 "d" 被自动赋予了键名 7。这是由于之前最大的整数键名是 6。
数组单元可以通过 array[key] 语法来访问。
Example #6 访问数组单元
<?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" ]);
?>
以上例程会输出:
string(3) "bar" int(24) string(3) "foo"
Note:
方括号和花括号可以互换使用来访问数组单元(例如 $array[42] 和 $array{42} 在上例中效果相同)。
自 PHP 5.4 起可以用数组间接引用函数或方法调用的结果。之前只能通过一个临时变量。
自 PHP 5.5 起可以用数组间接引用一个数组原型。
Example #7 数组间接引用
<?php
function getArray () {
return array( 1 , 2 , 3 );
}
// on PHP 5.4
$secondElement = getArray ()[ 1 ];
// previously
$tmp = getArray ();
$secondElement = $tmp [ 1 ];
// or
list(, $secondElement ) = getArray ();
?>
Note:
试图访问一个未定义的数组键名与访问任何未定义变量一样:会导致
E_NOTICE
级别错误信息,其结果为NULL
。
可以通过明示地设定其中的值来修改一个已有数组。
这是通过在方括号内指定键名来给数组赋值实现的。也可以省略键名,在这种情况下给变量名加上一对空的方括号([])。
$arr[key] = value; $arr[] = value; // key 可以是 integer 或 string // value 可以是任意类型的值
如果 $arr 还不存在,将会新建一个,这也是另一种新建数组的方法。不过并不鼓励这样做,因为如果 $arr 已经包含有值(例如来自请求变量的 string )则此值会保留而 [] 实际上代表着字符串访问运算符。初始化变量的最好方式是直接给其赋值。。
要修改某个值,通过其键名给该单元赋一个新值。要删除某键值对,对其调用 unset() 函数。
<?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:
如上所述,如果给出方括号但没有指定键名,则取当前最大整数索引值,新的键名将是该值加上 1(但是最小为 0)。如果当前还没有整数索引,则键名将为 0。
注意这里所使用的最大整数键名不一定当前就在数组中。它只要在上次数组重新生成索引后曾经存在过就行了。以下面的例子来说明:
<?php
// 创建一个简单的数组
$array = array( 1 , 2 , 3 , 4 , 5 );
print_r ( $array );
// 现在删除其中的所有元素,但保持数组本身不变:
foreach ( $array as $i => $value ) {
unset( $array [ $i ]);
}
print_r ( $array );
// 添加一个单元(注意新的键名是 5,而不是你可能以为的 0)
$array [] = 6 ;
print_r ( $array );
// 重新索引:
$array = array_values ( $array );
$array [] = 7 ;
print_r ( $array );
?>以上例程会输出:
Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) Array ( ) Array ( [5] => 6 ) Array ( [0] => 6 [1] => 7 )
有很多操作数组的函数,参见数组函数一节。
Note:
unset() 函数允许删除数组中的某个键。但要注意数组将不会重建索引。如果需要删除后重建索引,可以用 array_values() 函数。
<?php
$a = array( 1 => 'one' , 2 => 'two' , 3 => 'three' );
unset( $a [ 2 ]);
$b = array_values ( $a );
// Now $b is array(0 => 'one', 1 =>'three')
?>
foreach 控制结构是专门用于数组的。它提供了一个简单的方法来遍历数组。
应该始终在用字符串表示的数组索引上加上引号。例如用 $foo['bar'] 而不是 $foo[bar]。但是为什么呢?可能在老的脚本中见过如下语法:
<?php
$foo [ bar ] = 'enemy' ;
echo $foo [ bar ];
// etc
?>
这样是错的,但可以正常运行。那么为什么错了呢?原因是此代码中有一个未定义的常量(bar)而不是字符串('bar'-注意引号),而
PHP 可能会在以后定义此常量,不幸的是你的代码中有同样的名字。它能运行,是因为
PHP 自动将裸字符串(没有引号的字符串且不对应于任何已知符号)转换成一个其值为该裸字符串的正常字符串。例如,如果没有常量定义为
bar
,PHP 将把它替代为 'bar' 并使用之。
Note: 这并不意味着总是给键名加上引号。用不着给键名为常量或变量的加上引号,否则会使 PHP 不能解析它们。
<?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" ;
}
?>以上例程会输出:
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: 1Checking 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
演示此行为的更多例子:
<?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
// 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']" ;
// Concatenation is another option
print "Hello " . $arr [ 'fruit' ]; // Hello apple
?>
当打开 error_reporting 来显示
E_NOTICE
级别的错误(将其设为
E_ALL
)时将看到这些错误。默认情况下
error_reporting
被关闭不显示这些。
和在语法一节中规定的一样,在方括号(“[”和“]”)之间必须有一个表达式。这意味着可以这样写:
<?php
echo $arr [ somefunc ( $bar )];
?>
这是一个用函数返回值作为数组索引的例子。PHP 也可以用已知常量,可能之前已经见过:
<?php
$error_descriptions [ E_ERROR ] = "A fatal error has occured" ;
$error_descriptions [ E_WARNING ] = "PHP issued a warning" ;
$error_descriptions [ E_NOTICE ] = "This is just an informal notice" ;
?>
注意 E_ERROR 也是个合法的标识符,就和第一个例子中的 bar 一样。但是上一个例子实际上和如下写法是一样的:
<?php
$error_descriptions [ 1 ] = "A fatal error has occured" ;
$error_descriptions [ 2 ] = "PHP issued a warning" ;
$error_descriptions [ 8 ] = "This is just an informal notice" ;
?>
因为 E_ERROR 等于 1,等等。
也许有一天,PHP 开发小组可能会想新增一个常量或者关键字,或者用户可能希望以后在自己的程序中引入新的常量,那就有麻烦了。例如已经不能这样用 empty 和 default 这两个词了,因为他们是保留字。
Note: 重申一次,在双引号字符串中,不给索引加上引号是合法的因此 "$foo[bar]" 是合法的(“合法”的原文为 valid。在实际测试中,这么做确实可以访问数组的该元素,但是会报一个常量未定义的 notice。无论如何,强烈建议不要使用 $foo[bar]这样的写法,而要使用 $foo['bar'] 来访问数组中元素。--haohappy 注)。至于为什么参见以上的例子和字符串中的变量解析中的解释。
对于任意 integer , float , string , boolean 和 resource 类型,如果将一个值转换为数组,将得到一个仅有一个元素的数组,其下标为 0,该元素即为此标量的值。换句话说,(array)$scalarValue 与 array($scalarValue) 完全一样。
如果一个 object 类型转换为 array ,则结果为一个数组,其单元为该对象的属性。键名将为成员变量名,不过有几点例外:整数属性不可访问;私有变量前会加上类名作前缀;保护变量前会加上一个 '*' 做前缀。这些前缀的前后都各有一个 NULL 字符。这会导致一些不可预知的行为:
<?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 ());
?>
上例会有两个键名为 'AA',不过其中一个实际上是 '\0A\0A'。
将 NULL
转换为 array 会得到一个空的数组。
可以用 array_diff() 和数组运算符来比较数组。
PHP 中的数组类型有非常多的用途。以下是一些示例:
<?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').
?>
Example #8 使用 array()
<?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();
?>
Example #9 集合
<?php
$colors = array( 'red' , 'blue' , 'green' , 'yellow' );
foreach ( $colors as $color ) {
echo "Do you like $color ?\n" ;
}
?>
以上例程会输出:
Do you like red? Do you like blue? Do you like green? Do you like yellow?
直接改变数组的值自 PHP 5 起可以通过引用传递来做到。之前的版本需要需要采取变通的方法:
Example #10 在循环中改变单元
<?php
// PHP 5
foreach ( $colors as & $color ) {
$color = strtoupper ( $color );
}
unset( $color );
// Workaround for older versions
foreach ( $colors as $key => $color ) {
$colors [ $key ] = strtoupper ( $color );
}
print_r ( $colors );
?>
以上例程会输出:
Array ( [0] => RED [1] => BLUE [2] => GREEN [3] => YELLOW )
本例生成一个下标从 1 开始的数组。
Example #11 下标从 1 开始的数组
<?php
$firstquarter = array( 1 => 'January' , 'February' , 'March' );
print_r ( $firstquarter );
?>
以上例程会输出:
Array ( [1] => 'January' [2] => 'February' [3] => 'March' )
Example #12 填充数组
<?php
// fill an array with all items from a directory
$handle = opendir ( '.' );
while ( false !== ( $file = readdir ( $handle ))) {
$files [] = $file ;
}
closedir ( $handle );
?>
数组是有序的。也可以使用不同的排序函数来改变顺序。更多信息参见数组函数。可以用 count() 函数来数出数组中元素的个数。
Example #13 数组排序
<?php
sort ( $files );
print_r ( $files );
?>
因为数组中的值可以为任意值,也可是另一个数组。这样可以产生递归或多维数组。
Example #14 递归和多维数组
<?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" ;
?>
数组(Array) 的赋值总是会涉及到值的拷贝。使用引用运算符通过引用来拷贝数组。
<?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 $arr3 are the same
?>
[#1] florenxe [2015-10-07 18:53:45]
//a nice little way to print leap years using array
for ($leap = 2032; $leap < 2050; $leap+=4)
{
$arr = [];
array_push($arr, $leap);
foreach($arr as $a) {
echo ($a).PHP_EOL;
}
}
[#2] aditycse at gmail dot com [2015-08-10 09:23:11]
<?php
//Array can have following data type in key i.e string,integer
//Behaviour of array in case of array key has data type float or double
$exampleArray = array(0,
1,
"2.99999999" => 56,
2 => 2,
3.9999 => 3,
3 => 3.1,
true => 4,
false => 6,
);
//array structure
print_r($exampleArray);
//array of array keys
print_r(array_keys($exampleArray));
[#3] perske at uni-muenster dot de [2015-04-18 23:16:20]
Regarding this note: ??Strings containing valid integers will be cast to the integer type.??
This is true only for decimal integers without leading ??+??, but not for octal, hexadecimal, or binary integers.
Example:
<?php
$array = array(
"0" => "a",
"-1" => "b",
"+1" => "c",
"00" => "d",
"01" => "e",
"0x1" => "f",
);
var_dump($array);
?>
This example will output:
array(7) {
[0]=>
string(1) "a"
[-1]=>
string(1) "b"
["+1"]=>
string(1) "c"
["00"]=>
string(1) "d"
["01"]=>
string(1) "e"
["0x1"]=>
string(1) "f"
}
Thus different strings are always mapped to different array keys.
[#4] mathiasgrimm at gmail dot com [2014-09-29 16:20:22]
<?php
$a['a'] = null;
$a['b'] = array();
echo $a['a']['non-existent']; // DOES NOT throw an E_NOTICE error as expected.
echo $a['b']['non-existent']; // throws an E_NOTICE as expected
?>
I added this bug to bugs.php.net (https://bugs.php.net/bug.php?id=68110)
however I made tests with php4, 5.4 and 5.5 versions and all behave the same way.
This, in my point of view, should be cast to an array type and throw the same error.
This is, according to the documentation on this page, wrong.
From doc:
"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 be NULL."
[#5] brta dot akos at gmail dot com [2014-01-10 13:45:43]
Why not to user one-based arrays:
<?php
$a = array(1 => 'a', 'b', 'd');
print_r($a);
array_splice($a,2,0,'c');
print_r($a);
?>
output:
Array ( [1] => a [2] => b [3] => d ) Array ( [0] => a [1] => b [2] => c [3] => d )
[#6] note dot php dot lorriman at spamgourmet dot org [2014-01-09 15:01:55]
There is another kind of array (php>= 5.3.0) produced by
$array = new SplFixedArray(5);
Standard arrays, as documented here, are marvellously flexible and, due to the underlying hashtable, extremely fast for certain kinds of lookup operation.
Supposing a large string-keyed array
$arr=['string1'=>$data1, 'string2'=>$data2 etc....]
when getting the keyed data with
$data=$arr['string1'];
php does *not* have to search through the array comparing each key string to the given key ('string1') one by one, which could take a long time with a large array. Instead the hashtable means that php takes the given key string and computes from it the memory location of the keyed data, and then instantly retrieves the data. Marvellous! And so quick. And no need to know anything about hashtables as it's all hidden away.
However, there is a lot of overhead in that. It uses lots of memory, as hashtables tend to (also nearly doubling on a 64bit server), and should be significantly slower for integer keyed arrays than old-fashioned (non-hashtable) integer-keyed arrays. For that see more on SplFixedArray :
http://uk3.php.net/SplFixedArray
Unlike a standard php (hashtabled) array, if you lookup by integer then the integer itself denotes the memory location of the data, no hashtable computation on the integer key needed. This is much quicker. It's also quicker to build the array compared to the complex operations needed for hashtables. And it uses a lot less memory as there is no hashtable data structure. This is really an optimisation decision, but in some cases of large integer keyed arrays it may significantly reduce server memory and increase performance (including the avoiding of expensive memory deallocation of hashtable arrays at the exiting of the script).
[#7] ivegner at yandex dot ru [2013-08-28 08:43:28]
Note that objects of classes extending ArrayObject SPL class are treated as arrays, and not as objects when converting to array.
<?php
class ArrayObjectExtended extends ArrayObject
{
private $private = 'private';
public $hello = 'world';
}
$object = new ArrayObjectExtended();
$array = (array) $object;
// This will not expose $private and $hello properties of $object,
// but return an empty array instead.
var_export($array);
?>
[#8] chris at ocportal dot com [2013-05-28 09:01:11]
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.
[#9] gtisza at gmail dot com [2013-02-12 14:17:26]
Be very careful when using a result as an array.
<?php echo $a['foo']['bar']['baz'] ?>
will throw an error if $a is an object, and throw a warning if $a is an array but does not have the right keys, but it will silently return true if $a is null or boolean or int, and if $a is a string, it will return its first character. (This is true even with E_STRICT set.) This can be a major gotcha with functions which return null or false if they are unsuccessful.
[#10] martijntje at martijnotto dot nl [2012-03-29 07:48:35]
Please note that adding the magic __toString() method to your objects will not allow you to seek an array with it, it still throws an Illegal Offset warning.
The solution is to cast it to a string first, like this
$array[(string) $stringableObject]
[#11] mlvljr [2011-05-20 06:37:27]
please note that when arrays are copied, the "reference status" of their members is preserved (http://www.php.net/manual/en/language.references.whatdo.php).
[#12] Walter Tross [2010-08-12 11:04:39]
It is true that "array assignment always involves value copying", but the copy is a "lazy copy". This means that the data of the two variables occupy the same memory as long as no array element changes.
E.g., if you have to pass an array to a function that only needs to read it, there is no advantage at all in passing it by reference.
[#13] ken underscore yap atsign email dot com [2008-01-09 08:00:16]
"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.
[#14] carl at linkleaf dot com [2007-09-06 11:36:40]
Its worth noting that there does not appear to be any functional limitations on the length or content of string indexes. The string indexes for your arrays can contain any characters, including new line characters, and can be of any length:
<?php
$key = "XXXXX";
$test = array($key => "test5");
for ($x = 0; $x < 500; $x++) {
$key .= "X";
$value = "test" . strlen($key);
$test[$key] = $value;
}
echo "<pre>";
print_r($test);
echo "</pre>";
?>
Keep in mind that using extremely long array indexes is not a good practice and could cost you lots of extra CPU time. However, if you have to use a long string as an array index you won't have to worry about the length or content.
[#15] Spudley [2007-03-16 01:44:27]
On array recursion...
Given the following code:
<?php
$myarray = array('test',123);
$myarray[] = &$myarray;
print_r($myarray);
?>
The print_r() will display *RECURSION* when it gets to the third element of the array.
There doesn't appear to be any other way to scan an array for recursive references, so if you need to check for them, you'll have to use print_r() with its second parameter to capture the output and look for the word *RECURSION*.
It's not an elegant solution, but it's the only one I've found, so I hope it helps someone.
[#16] [2006-10-25 09:18:13]
This page should include details about how associative arrays are implemened inside PHP; e.g. using hash-maps or b-trees.
This has important implictions on the permance characteristics of associative arrays and how they should be used; e.g. b-tree are slow to insert but handle collisions better than hashmaps. Hashmaps are faster if there are no collisions, but are slower to retrieve when there are collisions. These factors have implictions on how associative arrays should be used.
[#17] ia [AT] zoznam [DOT] sk [2005-09-30 02:55:37]
Regarding the previous comment, beware of the fact that reference to the last value of the array remains stored in $value after the foreach:
<?php
foreach ( $arr as $key => &$value )
{
$value = 1;
}
// without next line you can get bad results...
//unset( $value );
$value = 159;
?>
Now the last element of $arr has the value of '159'. If we remove the comment in the unset() line, everything works as expected ($arr has all values of '1').
Bad results can also appear in nested foreach loops (the same reason as above).
So either unset $value after each foreach or better use the longer form:
<?php
foreach ( $arr as $key => $value )
{
$arr[ $key ] = 1;
}
?>
[#18] caifara aaaat im dooaat be [2005-08-28 02:28:08]
[Editor's note: You can achieve what you're looking for by referencing $single, rather than copying it by value in your foreach statement. See http://php.net/foreach for more details.]
Don't know if this is known or not, but it did eat some of my time and maybe it won't eat your time now...
I tried to add something to a multidimensional array, but that didn't work at first, look at the code below to see what I mean:
<?php
$a1 = array( "a" => 0, "b" => 1 );
$a2 = array( "aa" => 00, "bb" => 11 );
$together = array( $a1, $a2 );
foreach( $together as $single ) {
$single[ "c" ] = 3 ;
}
print_r( $together );
foreach( $together as $key => $value ) {
$together[$key]["c"] = 3 ;
}
print_r( $together );
?>
[#19] jeff splat codedread splot com [2005-04-21 09:16:32]
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("<br/>");
?>
<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 )
[#20] lars-phpcomments at ukmix dot net [2005-03-28 08:40:25]
Used to creating arrays like this in Perl?
@array = ("All", "A".."Z");
Looks like we need the range() function in PHP:
<?php
$array = array_merge(array('All'), range('A', 'Z'));
?>
You don't need to array_merge if it's just one range:
<?php
$array = range('A', 'Z');
?>