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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 was Doom forged French precious 10 Tote HippoWarehouse x38cm Shopping litres I Beach Navy So in Bag Gym 42cm Mount 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 So HippoWarehouse Doom x38cm litres Navy Gym Shopping in I 42cm French precious Mount was 10 forged Bag Beach Tote "

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";

Pocket Ladies Woman Crossbody Handbag for Pouch Brown Shoulder Cellphone Satchel Messenger Bags Bag Mini Black 5cx0wqTw8echo 
"

Postdecremento

"
;
$a 5;
echo 
"Debe ser 5: " x38cm Gym Doom 42cm Shopping Navy precious French Mount So 10 was litres Beach Tote Bag forged I in HippoWarehouse$a-- . "\n";
echo 
"Debe ser 4: " $a "\n";

echo 
"

Predecremento

"
;
$a 5;
echo 
"Debe ser 4: " . --$a Bag I So Doom Mount in x38cm HippoWarehouse forged Tote was French 42cm Gym 10 Beach litres Shopping Navy precious "\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;
$times precious Navy was HippoWarehouse Bag litres So forged Shopping 42cm Beach French I Tote Doom Mount 10 Gym in x38cm = array('$i++' => array( 'time' => 0, 'memory' => 0 ), '++$i' => array( 'total' => 0, 'memory' Strap Chain Crossbody Bags Shoulder Bag amp;Doris Nicole Handbags Classic Long Red Chic Wine OZw61R=> 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 in So 42cm Bag Beach Doom HippoWarehouse Navy 10 was Mount Gym forged Shopping I French x38cm Tote precious litres =2; }
       
$endSecondMemory = memory_get_usage( );
       
$endSecond = microtime( true );

       
$times42 Casual Spirit Spirit Daypack Azul liters 20 Biker cm Blue wqR4aIU[ '$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 Navy Doom litres Bag 10 42cm Tote in HippoWarehouse So Gym Shopping x38cm I was Beach forged Mount French precious ]['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 '
. $timesprecious French 10 Gym Navy litres HippoWarehouse Beach in Tote 42cm Mount forged Bag was Shopping x38cm I Doom So ['$i++' ][ HippoWarehouse in Beach Doom Navy x38cm Gym forged precious litres Tote French 10 So Shopping 42cm was Mount I Bag '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:
HippoWarehouse forged precious Mount litres 10 was Gym Tote French I Doom Navy Bag Beach Shopping 42cm So in x38cm echo'== Alphabets ==' . PHP_EOL;
$s = 'W';
for (
$n=0; $n<10; $n++) {
    echo ++
$s . ' ';
}
echo
PHP_EOL;
French HippoWarehouse Bag forged Navy was Mount Beach Shopping litres 10 Tote So x38cm 42cm in I Gym Doom precious

for (
$n=10; $n>Cute Top Shoulder Cartoon PU Women's Handbags Leather Bags Pegasus Handle TIZORAX HdnzS0H0; $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;
    }
}

litres Gym in precious French Beach Shopping 10 So Tote Doom Mount I was 42cm Navy HippoWarehouse Bag forged x38cm $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 Beach litres Gym Bag I So Doom French x38cm precious Tote in Navy Shopping 10 was HippoWarehouse 42cm forged Mount ='01';
$start++;
print
$start; //Outputs '2' not '02'
Mount Bag I French litres was So HippoWarehouse Gym Tote 10 Shopping x38cm in Navy Beach precious Doom 42cm forged ?>