Operators

An operator is something that takes one or more values (or expressions, in programming jargon) and yields another value (so that the construction itself becomes an expression).

Operators can be grouped according to the number of values they take. Unary operators take only one value, for example ! (the logical not operator) or ++ (the increment operator). Binary operators take two values, such as the familiar arithmetical operators + (plus) and - (minus), and the majority of PHP operators fall into this category. Finally, there is a single ternary operator, ? :, which takes three values; this is usually referred to simply as "the ternary operator" (although it could perhaps more properly be called the conditional operator).

A full list of PHP operators follows in the section Operator Precedence. The section also explains operator precedence and associativity, which govern exactly how expressions containing several different operators are evaluated.

211
Anonymous
15 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
24
yasuo_ohgaki at hotmail dot com
18 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.
ivijan dot stefan at gmail dot com
3 months ago
If you use "AND" and "OR", you'll eventually get tripped up by something like this:

<?php
\$this_one
= true;
\$that = false;
\$truthiness = \$this_one and \$that;
?>

Want to guess what \$truthiness equals?

If you said "false"  ...it's wrong!

"\$truthiness" above has the value "true". Why?  "=" has a higher precedence than "and". The addition of parentheses to show the implicit order makes this clearer:

<?php
(\$truthiness = \$this_one) and \$that;
?>

If you used "&&" instead of and in the first code example, it would work as expected and be "false".

This also works to get the correct value, as parentheses have higher precedence than "=":

<?php
\$truthiness
= (\$this_one and \$that);
?>
figroc at gmail dot com
11 years ago
The variable symbol '\$' should be considered as the highest-precedence operator, so that the variable variables such as \$\$a won't confuse the parser.  [http://www.php.net/manual/en/language.variables.variable.php]
-6
phpnet dot 20 dot dpnsubs at xoxy dot net
11 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'
?>
-34
me at robrosenbaum dot com
12 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.
-37
rick at nomorespam dot fourfront dot ltd dot uk
14 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 (  => 1  => 6  => 3 )
as if the code said;-
\$a=\$b;

Under a C compiler the result is;-
Array (  => 1  => 5  => 3 )
as if the code said;-
\$a=\$b;

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.
-42
golotyuk at gmail dot com
13 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 