Incrementing/Decrementing Operators

Incrementing/Decrementing Operators

PHP supports pre- and post-increment and decrement operators. Those unary operators allow to increment or decrement the value by one.

| Example | Name | Effect | | --- | --- | --- | | ++$a | Pre-increment | Increments by one, then returns . | | $a++ | Post-increment | Returns , then increments by one. | | --$a | Pre-decrement | Decrements by one, then returns . | | $a-- | Post-decrement | Returns , then decrements by one. |

Voorbeeld: Examples of Increment/Decrement

<?php
echo 'Post-increment:', PHP_EOL;
$a = 5;
var_dump($a++);
var_dump($a);

echo 'Pre-increment:', PHP_EOL;
$a = 5;
var_dump(++$a);
var_dump($a);

echo 'Post-decrement:', PHP_EOL;
$a = 5;
var_dump($a--);
var_dump($a);

echo 'Pre-decrement:', PHP_EOL;
$a = 5;
var_dump(--$a);
var_dump($a);
?>

Post-increment:
int(5)
int(6)
Pre-increment:
int(6)
int(6)
Post-decrement:
int(5)
int(4)
Pre-decrement:
int(4)
int(4)

Waarschuwing: > The increment and decrement operators have no effect on values of type . A is emitted as of PHP 8.3.0, because this will implicitly cast the value to in the future. bool``E_WARNING``int

The decrement operator has no effect on values
of type .
A  is emitted as of PHP 8.3.0,
because this will implicitly cast the value to  in the future.

null``E_WARNING``int

The decrement operator has no effect on non-
.
A  is emitted as of PHP 8.3.0,
because a  will be thrown in the future.

numeric stringE_WARNING``TypeError

Opmerking: > Internal objects that support overloading addition and/or subtraction can also be incremented and/or decremented. One such internal object is . GMP

PERL string increment feature

Waarschuwing: > This feature is soft-deprecated as of PHP 8.3.0. The function should be used instead. str_increment

It is possible to increment a non-

in PHP. The string must be an alphanumerical ASCII string. Which increments letters up to the next letter, when reaching the letter the increment is carried to the value on the left. For example, turns into . numeric stringZ``$a = 'Z'; $a++;``$a``'AA'

Voorbeeld: PERL string increment example

<?php
echo '== Alphabetic strings ==' . PHP_EOL;
$s = 'W';
for ($n=0; $n<6; $n++) {
    echo ++$s . PHP_EOL;
}
// Alphanumeric strings behave differently
echo '== Alphanumeric strings ==' . PHP_EOL;
$d = 'A8';
for ($n=0; $n<6; $n++) {
    echo ++$d . PHP_EOL;
}
$d = 'A08';
for ($n=0; $n<6; $n++) {
    echo ++$d . PHP_EOL;
}
?>

== Alphabetic strings ==
X
Y
Z
AA
AB
AC
== Alphanumeric strings ==
A9
B0
B1
B2
B3
B4
A09
A10
A11
A12
A13
A14

Waarschuwing: > If the alphanumerical string can be interpreted as a

it will be cast to an  or .
This is particularly an issue with strings that look like a floating point
numbers written in exponential notation.
The  function does not suffer from
these implicit type cast.

numeric stringint``float``str_increment

Voorbeeld: Alphanumerical string converted to float

<?php
$s = "5d9";
var_dump(++$s);
var_dump(++$s);
?>

string(3) "5e0"
float(6)

 This is because the value  is interpreted
 as a  and cast to the value 
 before being incremented.
`"5e0"``float``5.0`