PHP 5.6.22 is available

Operator Precedence

The precedence of an operator specifies how "tightly" it binds two expressions together. For example, in the expression 1 + 5 * 3, the answer is 16 and not 18 because the multiplication ("*") operator has a higher precedence than the addition ("+") operator. Parentheses may be used to force precedence, if necessary. For instance: (1 + 5) * 3 evaluates to 18. If operator precedence is equal, left to right associativity is used.

The following table lists the precedence of operators with the highest-precedence operators listed at the top of the table. Operators on the same line have equal precedence, in which case their associativity decides which order to evaluate them in.

Operator Precedence
Associativity Operators Additional Information
non-associative clone new clone and new
left [ array()
non-associative ++ -- increment/decrement
right ~ - (int) (float) (string) (array) (object) (bool) @ types
non-associative instanceof types
right ! logical
left * / % arithmetic
left + - . arithmetic and string
left << >> bitwise
non-associative < <= > >= <> comparison
non-associative == != === !== comparison
left & bitwise and references
left ^ bitwise
left | bitwise
left && logical
left || logical
left ? : ternary
right = += -= *= /= .= %= &= |= ^= <<= >>= => assignment
left and logical
left xor logical
left or logical
left , many uses

Left associativity means that the expression is evaluated from left to right, right associativity means the opposite.

Example #1 Associativity

<?php
$a 
5// (3 * 3) % 5 = 4
$a true true 2// (true ? 0 : true) ? 1 : 2 = 2

$a 1;
$b 2;
$a $b += 3// $a = ($b += 3) -> $a = 5, $b = 5
?>
Use parentheses to increase readability of the code.

Note:

Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.

add a note add a note

User Contributed Notes 9 notes

up
67
Antistone
2 years ago
BEWARE:  Addition, subtraction, and string concatenation have equal precedence!
<?
$x
= 4;
echo
"x minus one equals " . $x-1 . ", or so I hope";
?>
will print "-1, or so I hope"

(Concatenate the first string literal and the value of $x, then implicitly convert that to a number (zero) so you can subtract 1 from it, then concatenate the final string literal.)
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30
fabmlk
11 months ago
Watch out for the difference of priority between 'and vs &&' or '|| vs or':
<?php
$bool
= true && false;
var_dump($bool); // false, that's expected

$bool = true and false;
var_dump($bool); // true, ouch!
?>
Because 'and/or' have lower priority than '=' but '||/&&' have higher.
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11
nicoolasens at gmail dot com
7 months ago
Too add something ton Antistone's comment :
{Antistone ΒΆ
1 year ago
BEWARE:  Addition, subtraction, and string concatenation have equal precedence!
<?
$x
= 4;
echo
"x minus one equals " . $x-1 . ", or so I hope";
?>
will print "-1, or so I hope"

(Concatenate the first string literal and the value of $x, then implicitly convert that to a number (zero) so you can subtract 1 from it, then concatenate the final string literal.)
}

You can use the operator "," instead of ".".
This way allows you to concatenate the first string literal after $x-1.
So the first string literal is note convert to a number (zero) .
Solution :

<?php
$x
= 4;
echo
"x minus one equals " , $x-1 . ", or so I hope";
?>

will print :
"x minus one equals 3, or so I hope "
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24
Carsten Milkau
3 years ago
Beware the unusual order of bit-wise operators and comparison operators, this has often lead to bugs in my experience. For instance:

<?php if ( $flags & MASK  == 1) do_something(); ?>

will not do what you might expect from other languages. Use

<?php if (($flags & MASK) == 1) do_something(); ?>

in PHP instead.
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2
Bilal Mustafa
1 month ago
Another way to sort out the problem mentioned by "nicoolasens at gmail dot com" and "Antistone" is:

<?php
$x
= 4;
echo
"x minus one equals " . $x-1 . ", or so I hope";
?>
will print "-1, or so I hope"

Solution:

We can wrap the methematical part in "()" and let the parser tell to solve it first in other words here we can get the benefit of higher precedence of "()" So if we rewrite the example as:

<?php
$x
= 4;
echo
"x minus one equals " . ($x-1) . ", or so I hope";
?>

The answer will be according to our expectation which is:

"x minus one equals 3, or so I hope"
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3
karlisd at gmail dot com
6 months ago
Sometimes it's easier to understand things in your own examples.
If you want to play around operator precedence and look which tests will be made, you can play around with this:

<?php
function F($v) {echo $v." "; return false;}
function
T($v) {echo $v." "; return true;}

IF (
F(0) || T(1) && F(2)  || F(3)  && ! F(4) ) {
  echo
"true";
} else echo
" false";
?>
Now put in IF arguments f for false and t for true, put in them some ID's. Play out by changing "F" to "T" and vice versa, by keeping your ID the same. See output and you will know which arguments  actualy were checked.
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5
headden at karelia dot ru
6 years ago
Although example above already shows it, I'd like to explicitly state that ?: associativity DIFFERS from that of C++. I.e. convenient switch/case-like expressions of the form

$i==1 ? "one" :
$i==2 ? "two" :
$i==3 ? "three" :
"error";

will not work in PHP as expected
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0
Anonymous
1 year ago
The following example will output false
$a = 1;
$b = 1;

$c = $a + $a++;
$d = 1 + $b++;

if($c == $d){
    echo 'true';
}else{
    echo 'false';
}
up
0
leipie at gmail dot com
2 years ago
The precedence of the arrow operator (->) on objects seems to the highest of all, even higher then clone.

But you can't wrap (clone $foo)->bar() like this!
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