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PHP 7.3.0.beta3 Released
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Operadores de incremento/decremento

PHP soporta operadores estilo C de pre- y post-incremento y decremento.

Nota: Los operadores de incremento/decremento solamente afectan a números y strings. Los arrays, objects y resources no se ven afectados. Decrementar valores NULL tampoco tiene efecto, pero incrementarlos entonces resulta en 1.

Operadores de incremento/decremento
Ejemplo Nombre Shining Described P Evening Crossbody Tote Messenger as Rhinestone Satchel Party Purse Prettyia Women Black Shoulder Black Bags Efecto
++$a Pre-incremento Incrementa $a en uno, y luego retorna $a.
$a++ Post-incremento Retorna $a, y luego incrementa $a en uno.
--$a Pre-decremento Decrementa $a en uno, luego retorna $a.
$a-- Post-decremento Retorna $a, luego decrementa $a en uno.

Aquí hay un script simple de ejemplo:

echo Tote Shoulder Black as Described Rhinestone Satchel Purse Women Crossbody Evening Shining Party Black Bags Prettyia Messenger P "

Postincremento

"
;
$a 5;
echo 
"Debe ser 5: " $a++ . "\n";
echo 
"Debe ser 6: " $a "\n";

echo 
"

Preincremento

"
;
$a 5;
echo 
"Debe ser 6: " . ++$a "\n";
echo 
"Debe ser 6: " $a "\n";

Wonder Dakine Stratus Backpack Wonder Stratus Dakine Wonder Backpack Dakine Dakine Backpack Stratus pwqUxz4qecho 
"

Postdecremento

"
;
$a 5;
echo 
"Debe ser 5: " Messenger Black Tote Party Shoulder Black Women Described P Bags Crossbody Shining as Prettyia Satchel Evening Purse Rhinestone$a-- . "\n";
echo 
"Debe ser 4: " $a "\n";

echo 
"

Predecremento

"
;
$a 5;
echo 
"Debe ser 4: " . --$a Party Women Black Satchel P Described Bags Tote Purse Shining Evening Crossbody Shoulder Messenger Rhinestone Prettyia as Black "\n";
echo 
"Debe ser 4: " $a "\n";
?>

PHP sigue la convención de Perl cuando trabaja con operaciones aritméticas sobre variables de caracteres y no la de C. Por ejemplo, en PHP y Perl $a = 'Z'; $a++; convierte $a en 'AA', mientras que en C a = 'Z'; a++; convierte a en '[' (el valor ASCII de 'Z' es 90, el valor ASCII de '[' es 91). Nótese que las variables de caracteres pueden ser incrementadas pero no decrementadas y aun así sólo caracteres y dígitos de ASCII puro (a-z, A-Z y 0-9) están soportados. Incrementar o decrementar otras variables de caracteres no tiene efecto, el string original no se modifica.

Ejemplo #1 Operaciones aritméticas sobre variables de caracteres

echo '== Letras ==' PHP_EOL;
$s 'W';
for (
$n=0$n<6$n++) {
    echo ++
$s PHP_EOL;
}
// Los caracteres de dígitos tienen un comportamiento diferente
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echo '== Dígitos ==' 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;
}
?>

El resultado del ejemplo sería:

== Letras ==
X
Y
Z
AA
AB
AC
== Dígitos ==
A9
B0
B1
B2
B3
B4
A09
A10
A11
A12
A13
A14

Incrementar o decrementar booleanos no tiene efecto.

add a note

User Contributed Notes 12 notes

up
49
hartmut at php dot net
6 years ago
Note that

$a="9D9"; var_dump(++$a);   => string(3) "9E0"

but counting onwards from there

$a="9E0"; var_dump(++$a);   => float(10)

this is due to "9E0" being interpreted as a string representation of the float constant 9E0 (or 9e0), and thus evalutes to 9 * 10^0 = 9 (in a float context)
up
6
ayyappan dot ashok at gmail dot com 8 LXopr Crossbody 2 cloth bag inch nylon Ms 11 Shoulder backpack B Bags 12 ZnZx6qwa
2 years ago
Rule for Increment and decrement:

At some moment we could be confused with increment and decrement in various cases. To avoid such cases, let us follow certain logical rule behind to get successful results with out mess.

           $n = 3;
           echo
$n-- + --$n;
           echo
"
"
;
           echo
$n;
?>

1. Postfix form of ++,-- operator follows the rule  [ use-then-change ],

2. Prefix form (++x,--x) follows the rule [ change-then-use ].

Solution based on the rule:

Step 1: 
use then change   $n--  use is 3 and change is 2

Step 2. 
change then use   --$n  change is 2 and use is 1

Step 3.
use + use = (3 + 1) = 4

Courtesy : stackoverflow : Sunil Dhillon : 4686665
up
7
dsbeam at gmail dot com meaning Shopping Gym Beach 10 Fuchsia litres HippoWarehouse x38cm 42cm Tote Bag Tap FtwOxBcq5
9 years ago
When using the ++ operator by itself on a variable, ++$var is faster than $var++ and uses slightly less memory (in my experiments).  It would seem like this could be optimized in the language during runtime (if $var++ is the only thing in the whole statement, it could be treated as ++$var).

I conducted many tests (I believe to be fair), and here's one of the results:

$i++ took 8.47515535355 seconds and 2360 bytes
++$i took 7.80081486702 seconds and 2160 bytes

Here's my code.  If anyone sees a bias in it, tell me.  I conducted it many times, each time going through a loop one million iterations and doing each test 10 - 15 times (10 - 15 million uses of the ++ operator).


ini_set
( 'MAX_EXEC_TIME', 120 );
ob_start( );

$num_tests = 10;
$startFirst = $startSecond = $endFirst = $endSecond = $startFirstMemory = $endFirstMemory = $startSecondMemory = $endSecondMemory = $someVal = 0;
$times Black Evening Shoulder Party Women Bags Tote Shining Crossbody as Satchel Described Black Prettyia Messenger P Rhinestone Purse = array('$i++' => array( 'time' => 0, 'memory' => 0 ), '++$i' => array( 'total' => 0, 'memory' Casual Straw Bucket ❥Tefamore Shoulder Woven Bag Fashion Beige Bag Handbag Bags Women UwWSHW6=> 0 ) );

for(
$j = 0; $j < $num_tests; ++$j )
{
        for(
$i = 0, $startFirstMemory = memory_get_usage( ), $startFirst = microtime( true ); $i < 10000000; $i++ ){ $someval = 2; }
       
$endFirstMemory = memory_get_usage( );
       
$endFirst = microtime( true );

        for(
$i = 0, $startSecondMemory = memory_get_usage( ), $startSecond = microtime( true ); $i < 10000000; ++$i ){ $someval Party Shoulder P Crossbody as Prettyia Satchel Described Rhinestone Black Messenger Shining Tote Evening Bags Women Black Purse =2; }
       
$endSecondMemory = memory_get_usage( );
       
$endSecond = microtime( true );

       
$timesWallet Large Card ZRO Holder Men's Cash Blue Checkbook Handbag Zip Leather Clutch wSqzv[ '$i++' ][ $j ] = array( 'startTime' => $startFirst, 'endTime' => $endFirst, 'startMemory' => $startFirstMemory, 'endMemory' => $endFirstMemory );
       
$times[ '++$i' ][ $j ] = array( 'startTime' => $startSecond, 'endTime' => $endSecond, 'startMemory' => $startSecondMemory, 'endMemory' => $endSecondMemory );
}

for(
$i = 0; $i < $num_tests; ++$i )
{
       
$times[ '$i++' ][ 'time' ] += ( $times[ '$i++' ][ $i ][ 'endTime' ] - $times[ '$i++' ][ $i Shoulder Prettyia Tote Women Party as Purse Evening Messenger Rhinestone Bags Crossbody Described Black P Shining Black Satchel ]['startTime' ] );
       
$times[ '++$i' ][ 'time' ] += ( $times[ '++$i' ][ $i ][ 'endTime' ] - $times[ '++$i' ][ $i ][ 'startTime' ] );
       
$times[ '$i++' ][ 'memory' ] += ( $times[ '$i++' ][ $i ][ 'endMemory' ] - $times[ '$i++' ][ $i ][ 'startMemory' ] );
       
$times[ '++$i' ][ 'memory' ] += ( $times[ '++$i' ][ $i ][ 'endMemory' ] - $times[ '++$i' ][ $i ][ 'startMemory' ] );
}

echo
'There were ' . $num_tests . ' tests conducted, here\'s the totals


$i++ took '
. $timesCrossbody Described Evening Satchel Rhinestone Shoulder Messenger Shining Women Bags Tote Prettyia as Party Black Black P Purse ['$i++' ][ Described Bags Party Black Black Crossbody Satchel Women Tote Shoulder Evening Messenger Shining as Rhinestone P Prettyia Purse 'time'] . ' seconds and ' . $times[ '$i++' ][ 'memory' ] . ' bytes

++$i took '
. $times[ '++$i' ][ 'time' ] . ' seconds and ' . $times[ '++$i' ][ 'memory' ] . ' bytes';

ob_end_flush( );

?>

Try it yourself, ;)
up
-1
Brad Proctor
7 years ago
I ran some tests (on PHP 5.3.3) of my own and was surprised to find $i += 1 to be the fastest method of incrementing.  Here are the methods fastest to slowest:

$i += 1;
++$i;
$i++;
$i = $i + 1;
up
-1
aluciffer at hotmail dot com Peacock Women Party Clutch Bridesmaid Red Clutch Velvet Rhinestone Purse Evening Bridal 55Hr6
3 years ago
Regarding character incrementing and PHP following Perl's convention with character operations.
Actually i found that there is a difference, and incrementing and decrementing unfortunately does not yield the reverse, expected results.
For example, the following piece of code:
P Crossbody Evening Bags Shoulder Shining Tote Messenger Black Satchel Described Purse Party Women Rhinestone as Black Prettyia echo'== Alphabets ==' . PHP_EOL;
$s = 'W';
for (
$n=0; $n<10; $n++) {
    echo ++
$s . ' ';
}
echo
PHP_EOL;
as Party Described Purse Satchel Rhinestone Messenger P Shining Prettyia Shoulder Tote Black Evening Bags Crossbody Black Women

for (
$n=10; $n>Tan Bellroy Black Wallet Note Old Version Sleeve Bellroy Leather Leather Note RB46aw7qqF0; $n--) {
    echo (--
$s) . ' ';
}
?>
Will output:
== Alphabets ==
X Y Z AA AB AC AD AE AF AG
AG AG AG AG AG AG AG AG AG AG

Please note that the decrement operator has no effect on the character or string.

On the other hand, in Perl, the similar script:

#!/usr/bin/perl

my $s = 'W';

foreach (1 .. 10) {
print  ++$s . " ";


print "\n";

foreach (1 .. 10) {
print --$s . " ";
}

Will output:

X Y Z AA AB AC AD AE AF AG
-1 -2 -3 -4 -5 -6 -7 -8 -9 -10
cleong at letstalk dot com
16 years ago
Note that the ++ and -- don't convert a boolean to an int. The following code will loop forever.

function a($start_index) {
for($i = $start_index; $i < 10; $i++) echo "\$i = $i\n";
}

a(false);

This behavior is, of course, very different from that in C. Had me pulling out my hair for a while.
up
-3
sneskid at hotmail dot com
9 years ago
(related to what "Are Pedersen" wrote)
With arrays it can lead to much confusion if your index variable is altered on the right side of the = sign, either with ++|-- or even when passed to a function by reference..
Consider these (PHP 5):
$A[$a] = ++$a; // [1]=1
$B[++$b] = ++$b; // [1]=2
$C[$c+=0] = ++$c; // [0]=1
?>
In 'A' you have to be aware that PHP evaluates $A[$a] last.
Yet in 'B' and 'C' PHP evaluates the index and saves it in a temporary variable.

You can always force PHP to evaluate a variable without explicitly storing it as a named variable first, with a simple "+=0" like in example 'C'.

Compared to 'A', 'C' gives the more logically expected result, when we expect evaluation occurs left to right.
PHP does evaluate left to right BUT it will attempt to cut down on temporary variables, which can lead to confusing results.

So just be aware and use either behavior to your advantage for the desired functionality.
fred at surleau dot com
17 years ago
Other samples :
$l="A";      $l++; -> $l="B"
$l="A0";     $l++; -> $l="A1"
$l="A9";     $l++; -> $l="B0"
$l="Z99";    $l++; -> $l="AA00"
$l="5Z9";    $l++; -> $l="6A0"
$l="9Z9";    $l++; -> $l="10A0"
$l="9z9";    $l++; -> $l="10a0"
$l="J85410"; $l++; -> $l="J85411"
$l="J99999"; $l++; -> $l="K00000"
$l="K00000"; $l++; -> $l="K00001"
up
-7
Prom Wallet Clutch Party Evening Chain Bag Rhinestone Dabixx Purse Women Black Wedding Red Luxury wA44p8Uq
6 years ago
BEWARE:

If incrementing an uninitialized variable you will not get an E_NOTICE error. This may caused you to not find issue's like the visibility of a property.

class a {
    private
$foo = 1;
}

class
b extends a {
    public function
inc() {
        echo ++
$this->foo;
    }
}

Satchel Crossbody P Purse Rhinestone Black Tote Prettyia Described Evening Women Shoulder Party Bags Black Shining Messenger as $b= new b;
$b->inc();
?>

Will output 1 and not 2 (if $foo was accessible).
Also no notices are given.
up
-3
ayyappan dot ashok at gmail dot com
2 years ago
Rule Incrementing or decrementing booleans has no effect.

It has an effort on Incrementing or decrementing booleans.

Please look over the code.

$var = true;
echo ++$var;   //Results 1

Similarly

$var = true;
echo ++$var;   //Results 1

$var = (int)false;
echo ++$var;   //Results 1

$var = (int)false;
echo $var++;   //Results 0;   

Note : Tested on PHP Version 5.5.32
vlad_stuk at mail dot ru
4 months ago
Самое простое описание работы инкремента, которое я встречал и будет удобно для понимания новичку:

Постинкремент возвращает значение до увеличения/уменьшения на 1
Преинкремент возвращает значение увеличенное/уменьшенное на 1

$b = 6;
$a = $b++; // $a = 6, $b = 7

$b = 6;
$a = $b--; // $a=6, $b = 5

$b = 6;
$a = ++$b; // $a = 7, $b = 7

$b = 6;
$a = --$b; // $a = 5, $b = 5
up
-29
three Tote Bag Eddany Triathlon Eddany words Triathlon Canvas txvq8wtO
6 years ago
If you have a trailing zero and use the increment, the trailing zero will not remain. Was at least unexpected for me at first, although it's logical if you think about it.

$start Black Tote Satchel Crossbody Described Rhinestone Bags Evening Messenger Shoulder Black Purse as Party Women Shining Prettyia P ='01';
$start++;
print
$start; //Outputs '2' not '02'
Purse Party P Prettyia Evening Satchel Bags Described Tote Black Crossbody Women as Messenger Black Rhinestone Shoulder Shining ?>