PHP 5.4.33 Released

연산자

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연산자는 하나 이상의 값(또는, 프로그래밍 은어로 표현)을 받아서 다른 값을 산출합니다. (그러므로 구조 자체는 표현이 됩니다) 그러므로 (print처럼) 값을 반환하는 함수나 구조를 연산자로 생각할 수 있고, (echo처럼) 아무것도 반환하지 않는 것을 다른 것으로 생각할 수 있습니다.

세 종류의 연산자가 있습니다. 첫번째는 하나의 값에만 작용하는 일항 연산자입니다. 예를 들면, !(부정 연산자)나 ++(증가 연산자)가 있습니다. 두번째는 이항 연산자로 불립니다; 이 종류는 PHP가 지원하는 대부분의 연산자에 해당합니다. 목록은 아래의 연산자 우선권 섹션에 있습니다.

세번째는 삼항 연산자입니다: ?:. 이것은 세번째에 의존해서 두 표현 중 하나를 선택하는 데 사용합니다. 삼항 연산자를 괄호로 감싸는 건 매우 좋은 생각입니다.

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User Contributed Notes 12 notes

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46
Anonymous
10 years ago
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
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6
figroc at gmail dot com
6 years ago
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]
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5
yasuo_ohgaki at hotmail dot com
13 years ago
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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-2
golotyuk at gmail dot com
8 years ago
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
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-4
rick at nomorespam dot fourfront dot ltd dot uk
9 years ago
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.
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-5
me at robrosenbaum dot com
7 years ago
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.
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-8
phpnet dot 20 dot dpnsubs at xoxy dot net
6 years ago
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:

<?php
$a
= 2;

echo (
$a == 1 ? 'one' :
        (
$a == 2 ? 'two' :
        (
$a == 3 ? 'three' :
        (
$a == 4 ? 'four' : 'other') ) ) );
echo
"\n";
//prints 'two'
?>
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-7
janturon at email dot cz
6 years ago
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";
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-11
madcoder at gmail dot com
7 years ago
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.
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-19
ddascalescu at gmail dot com
5 years ago
The -> operator, not listed above, is called "object operator" (T_OBJECT_OPERATOR).
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-18
pgarvin76+php dot net at NOSPAMgmail dot com
5 years ago
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
*/
?>
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-18
Gautam
6 years ago
<?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
*/
?>
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