Reference — What does this symbol mean in PHP?
What is this?
This is a collection of questions that come up every now and then about syntax in PHP. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.
Why is this?
It used to be hard to find questions about operators and other syntax tokens.¹
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the PHP Manual.
¹ Note: Since January 2013, Stack Overflow does support special characters. Just surround the search terms by quotes, eg [php] "==" vs "==="
What should I do here?
If you have been pointed here by someone because you have asked such a question, please find the particular syntax below. The linked pages to the PHP manual along with the linked questions will likely answer your question then. If so, you are encouraged to upvote the answer. This list is not meant as a substitute to the help others provided.
The List
If your particular token is not listed below, you might find it in the List of Parser Tokens.
& Bitwise Operators or References
=& References
&= Bitwise Operators
&& Logical Operators
% Arithmetic Operators
!! Logical Operators
@ Error Control Operators
?: Ternary Operator
?? Null Coalesce Operator (since PHP 7)
: Alternative syntax for control structures, Ternary Operator
:: Scope Resolution Operator
Namespaces
-> Classes And Objects
=> Arrays
^ Bitwise Operators
>> Bitwise Operators
<< Bitwise Operators
<<< Heredoc or Nowdoc
= Assignment Operators
== Comparison Operators
=== Comparison Operators
!== Comparison Operators
!= Comparison Operators
<> Comparison Operators
<=> Comparison Operators (since PHP 7.0)
| Bitwise Operators
|| Logical Operators
~ Bitwise Operators
+ Arithmetic Operators, Array Operators
+= and -= Assignment Operators
++ and -- Incrementing/Decrementing Operators
.= Assignment Operators
. String Operators
, Function Arguments
, Variable Declarations
$$ Variable Variables
` Execution Operator
<?= Short Open Tags
[] Arrays (short syntax since PHP 5.4)
$var = [] empty array <? Opening and Closing tags
... Argument unpacking (since PHP 5.6)
** Exponentiation (since PHP 5.6)
# One-line shell-style comment
Incrementing / Decrementing Operators
++ increment operator
-- decrement operator
Example Name Effect
---------------------------------------------------------------------
++$a Pre-increment Increments $a by one, then returns $a.
$a++ Post-increment Returns $a, then increments $a by one.
--$a Pre-decrement Decrements $a by one, then returns $a.
$a-- Post-decrement Returns $a, then decrements $a by one.
These can go before or after the variable.
If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.
For example:
$apples = 10;
for ($i = 0; $i < 10; ++$i) {
echo 'I have ' . $apples-- . " apples. I just ate one.n";
}
Live example
In the case above ++$i is used, since it is faster. $i++ would have the same results.
Pre-increment is a little bit faster, because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.
However, you must use $apples-- , since first you want to display the current number of apples, and then you want to subtract one from it.
You can also increment letters in PHP:
$i = "a";
while ($i < "c") {
echo $i++;
}
Once z is reached aa is next, and so on.
Note that character variables can be incremented but not decremented and even so only plain ASCII characters (az and AZ) are supported.
Stack Overflow Posts:
Bitwise Operator
What is a bit? A bit is a representation of 1 or 0. Basically OFF(0) and ON(1)
What is a byte? A byte is made up of 8 bits and the highest value of a byte is 255, which would mean every bit is set. We will look at why a byte's maximum value is 255.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
This representation of 1 Byte
1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 (1 Byte)
A few examples for better understanding
The "AND" operator: &
$a = 9;
$b = 10;
echo $a & $b;
This would output the number 8. Why? Well let's see using our table example.
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| & | 0| 0| 0| 0| 1| 0| 0| 0|
-------------------------------------------
So you can see from the table the only bit they share together is the 8 bit.
Second example
$a = 36;
$b = 103;
echo $a & $b; // This would output the number 36.
$a = 00100100
$b = 01100111
The two shared bits are 32 and 4, which when added together return 36.
The "Or" operator: |
$a = 9;
$b = 10;
echo $a | $b;
This would output the number 11. Why?
-------------------------------------------
| 1 Byte ( 8 bits ) |
-------------------------------------------
|Place Value | 128| 64| 32| 16| 8| 4| 2| 1|
-------------------------------------------
| $a | 0| 0| 0| 0| 1| 0| 0| 1|
-------------------------------------------
| $b | 0| 0| 0| 0| 1| 0| 1| 0|
-------------------------------------------
| | | 0| 0| 0| 0| 1| 0| 1| 1|
-------------------------------------------
You will notice that we have 3 bits set, in the 8, 2, and 1 columns. Add those up: 8+2+1=11.
_ Alias for gettext()
The underscore character '_' as in _() is an alias to the gettext() function.
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