Last updated: Fri, 06 Nov 2009

演算子

演算子とは、ひとつ以上の値 (あるいはプログラミング用語における「式」) から別の値 (制御構造が式になるように) を生み出すものです。つまり、値を返す関数や制御構造 (たとえば print) は演算子と考えられますし、何も値を返さないもの (たとえば echo) はそれ以外のものとなります。

演算子には 3 種類あります。ひとつめは単項演算子で、これはひとつの値に対してのみ作用します。例えば ! (否定演算子) や ++ (加算子) などです。ふたつめは二項演算子と呼ばれるものです。PHP がサポートしている演算子のほとんどはここに含まれ、その一覧は演算子の優先順位にあります。

最後のグループは、三項演算子 ?: です。これは、2 つの文や実行経路から選択するというよりも、3 番目の式に応じて 2 つの式から選択するために使用されるべきです。この演算子を使用する式は、括弧で囲んでおくことをお勧めします。

演算子の優先順位

式

Last updated: Fri, 06 Nov 2009

add a note User Contributed Notes
演算子

pgarvin76+php dot net at NOSPAMgmail dot com
30-Dec-2008 12:43


Method chaining is read left to right (left associative):

<?php



class Test_Method_Chain

{

    public function One()

    {

        echo "One" . PHP_EOL;

        return $this;

    }



    public function Two()

    {

        echo "Two" . PHP_EOL;

        return $this;

    }



    public function Three()

    {

        echo "Three" . PHP_EOL;

        return $this;

    }

}



$test = new Test_Method_Chain();



$test->One()->Two()->Three();



/* Ouputs:

One

Two

Three

*/

?>

ddascalescu at gmail dot com
24-Oct-2008 01:53


The -> operator, not listed above, is called "object operator" (T_OBJECT_OPERATOR).

figroc at gmail dot com
02-Aug-2008 10:30


The variable symbol '$' should be considered as the highest-precedence operator, so that the variable variables such as $$a[0] won't confuse the parser.  [http://www.php.net/manual/en/language.variables.variable.php]

phpnet dot 20 dot dpnsubs at xoxy dot net
01-Nov-2007 10:13


Note that in php the ternary operator ?: has a left associativity unlike in C and C++ where it has right associativity.





You cannot write code like this (as you may have accustomed to in C/C++):


<?php


$a = 2;


echo (


    $a == 1 ? 'one' : 


    $a == 2 ? 'two' : 


    $a == 3 ? 'three' : 


    $a == 4 ? 'four' : 'other');


echo "\n";


// prints 'four'


?>





You need to add brackets to get the results you want:


<?


$a = 2;





echo ($a == 1 ? 'one' : 


        ($a == 2 ? 'two' : 


        ($a == 3 ? 'three' : 


        ($a == 4 ? 'four' : 'other') ) ) );


echo "\n";


//prints 'two'





?>

Gautam
10-Oct-2007 10:22


<?php



$result1 = 7 + 8 * 9/3 -4;

$result2 = 7 + 8 * (9/3 -4);

$result3 =(7 + 8)* 9/3 -4;



echo "Result1 for 7 + 8 * 9/3 -4 = $result1  Result2 for 7 + 8 * (9/3 -4) = $result2 and Result3 (7 + 8)* 9/3 -4 = $result3 "

/*

 which gives results as under

 Result1 for 7 + 8 * 9/3 -4 = 27 Result2 for 7 + 8 * (9/3 -4) = -1 and Result3 (7 + 8)* 9/3 -4 = 41

 Execution Order is 1) expression in brackets 2) division 3) multiplication 4) addition and 5) subtraction 

*/

?>

janturon at email dot cz
08-Oct-2007 01:42


This is very common problem: set one variable to another, if it is not empty. If it is, set it to something else.

For example: set $bar to $foo, if $foo is empty, set $bar to "undefined";



if(!empty($foo)) $bar= $foo; else $bar= "undefined";



OR operator can shorten it:



$bar= @$foo or $bar= "undefined";

me at robrosenbaum dot com
12-Jul-2007 07:16


The scope resolution operator ::, which is missing from the list above, has higher precedence than [], and lower precedence than 'new'. This means that self::$array[$var] works as expected.

madcoder at gmail dot com
09-Jun-2007 10:17


In response to mathiasrav at gmail dot com:



The reason for that behavior is the parentheses.  From the description:



"Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18."



So the order of operations says that even though the equality operator has higher precedence, the parentheses in your statement force the assignment operator to a higher precedence than the equality operator.



That said, it still doesn't work the way you expect it to.  Neither way works, for these reasons:

<?php

if ( $a != ($a = $b) )

?>



Order of operations says to do the parentheses first.  So you end up with:

<?php

$a = $b;

if ( $a != $a )

?>



Which is obviously going to be false.  Without the parentheses:

<?php

if ( $a != $a = $b )

?>



Order of operations says to do the inequality first, then the assignment, so you have:

<?php

if ( $a != $a );

$a = $b;

?>



Which again is not what you expected, and again will always be false.  But because you are only working with values of 0 and 1, you can make use of the XOR operator:



<?php

if ( $a ^= $b )

?>



This will only be true if 1) $a is 0 and $b is 1, or 2) $a is 1 and $b is 0.  That is precisely what you wanted, and it even does the assignment the way you expected it to.



<?php

foreach ($ourstring as $c) {

  if ($bold ^= $c['bold']) $resstring .= bold;

  if ($underline ^= $c['underline']) $resstring .= underline;

  $resstring .= $c[0];

}

?>



That code now works and produces the output you expected.

golotyuk at gmail dot com
09-Jul-2006 04:51


Simple POST and PRE incremnt sample:



<?php



$b = 5;

$a = ( ( ++$b ) > 5 ); // Pre-increment test

echo (int)$a;



$b = 5;

$a = ( ( $b++ ) > 5 ); // Post-increment test

echo (int)$a;



?>



This will output 10, because of the difference in post- and pre-increment operations

rick at nomorespam dot fourfront dot ltd dot uk
02-Sep-2005 10:51


A quick note to any C developers out there, assignment expressions are not interpreted as you may expect - take the following code ;-



<?php

$a=array(1,2,3);

$b=array(4,5,6);

$c=1;



$a[$c++]=$b[$c++];



print_r( $a ) ;

?>



This will output;-

Array ( [0] => 1 [1] => 6 [2] => 3 )

as if the code said;-

$a[1]=$b[2];



Under a C compiler the result is;-

Array ( [0] => 1 [1] => 5 [2] => 3 )

as if the code said;-

$a[1]=$b[1];



It would appear that in php the increment in the left side of the assignment is processed prior to processing the right side of the assignment, whereas in C, neither increment occurs until after the assignment.

10-Jun-2004 12:58


of course this should be clear, but i think it has to be mentioned espacially:



AND is not the same like &&



for example:



<?php $a && $b || $c; ?>

is not the same like

<?php $a AND $b || $c; ?>



the first thing is

(a and b) or c



the second

a and (b or c)



'cause || has got a higher priority than and, but less than &&



of course, using always [ && and || ] or [ AND and OR ] would be okay, but than you should at least respect the following:



<?php $a = $b && $c; ?>

<?php $a = $b AND $c; ?>



the first code will set $a to the result of the comparison $b with $c, both have to be true, while the second code line will set $a like $b and THAN - after that - compare the success of this with the value of $c



maybe usefull for some tricky coding and helpfull to prevent bugs :D



greetz, Warhog

yasuo_ohgaki at hotmail dot com
26-Mar-2001 07:53


Other Language books' operator precedence section usually include "(" and ")" - with exception of a Perl book that I have. (In PHP "{" and "}" should also be considered also). However, PHP Manual is not listed "(" and ")" in precedence list. It looks like "(" and ")" has higher precedence as it should be.





Note: If you write following code, you would need "()" to get expected value.





<?php


$bar = true;


$str = "TEST". ($bar ? 'true' : 'false') ."TEST";


?>





Without "(" and ")" you will get only "true" in $str. 


(PHP4.0.4pl1/Apache DSO/Linux, PHP4.0.5RC1/Apache DSO/W2K Server)


It's due to precedence, probably.

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演算子の優先順位

式

Last updated: Fri, 06 Nov 2009

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