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declare

(PHP 4, PHP 5, PHP 7)

A instrução declare é usada para definir diretivas de execução para um bloco de código. A sintaxe do declare é similar à sintaxe de outros construtos de controle de fluxo:

declare (directive)
    statement

A seção directive permite que o comportamento do bloco do declare seja definido. Atualmente três diretivas são reconhecidas: a diretiva ticks (Veja abaixo para mais informações da diretiva ticks), a diretiva encoding (Veja abaixo para mais informações da diretiva encoding) e a diretiva strict_types (Veja abaixo para mais informações na seção strict sobre argumentos de função).

Versão Descrição
5.3.0 Adicionada a diretiva encoding
7.0.0 Adicionada a diretiva strict_types

Como as diretivas são manipuladas na compilação do arquivo, somente literais podem ser usadas como valores da diretiva. Variáveis e constantes não podem ser usadas. Para ilustrar:

<?php
// Isto é válido:
declare(ticks=1);

// isto é inválido:
const TICK_VALUE 1;
declare(
ticks=TICK_VALUE);
?>

A declaração parte do bloco do declare será executada - como é executada e quais os efeitos colaterais que ocorrem durante a execução depende da diretiva definida no bloco directive.

O construtor do declare também pode ser usado no escopo global, afetando todo o código que o segue (entretanto se o arquivo com o declare for incluído, não afetará o arquivo principal).

<?php
// these are the same:

// you can use this:
declare(ticks=1) {
    
// entire script here
}

// or you can use this:
declare(ticks=1);
// entire script here
?>

Ticks

Um 'tick' é um evento que ocorre a cada N declarações de baixo nível executadas pelo interpretador dentro do bloco declare. O valor de N é especificado usando ticks=N dentro do bloco declare da seção directive.

Nem todas declarações são passiveis de executar um 'tick'. Normalmente, expressões de condições e argumentos de expressões não são.

O(s) evento(s) que serão executados a cada tick são especificados usando a função register_tick_function(). Veja o exemplo abaixo para mais detalhes. Note que mais de um evento pode ser executado para cada tick.

Exemplo #1 Exemplo de uso do Tick

<?php

declare(ticks=1);

// A function called on each tick event
function tick_handler()
{
    echo 
"tick_handler() called\n";
}

register_tick_function('tick_handler');

$a 1;

if (
$a 0) {
    
$a += 2;
    print(
$a);
}

?>

Exemplo #2 Exemplo de uso dos Ticks

<?php

function tick_handler()
{
  echo 
"tick_handler() called\n";
}

$a 1;
tick_handler();

if (
$a 0) {
    
$a += 2;
    
tick_handler();
    print(
$a);
    
tick_handler();
}
tick_handler();

?>

Veja mais sobre register_tick_function() e unregister_tick_function().

Codificação

A codificação de um script pode ser especificada, por script, utilizando a diretiva encoding.

Exemplo #3 Declarando um encoding para o script.

<?php
declare(encoding='ISO-8859-1');
// code here
?>

Cuidado

Quando usada com namespaces, a única sintaxe válida para declarar é declare(encoding='...'); onde ... é o valor do encoding. declare(encoding='...') {} irá resultar em um erro de sintaxe quando usada com namespaces.

O valor de codificação em declare será ignorada no PHP 5.3 exceto se compilado com --enable-zend-multibyte.

Note que o PHP não mostra se --enable-zend-multibyte foi usada na compilação, com exceção da utilização da função phpinfo().

Veja mais zend.script_encoding.

add a note add a note

User Contributed Notes 14 notes

up
40
Anonymous
8 years ago
It's amazing how many people didn't grasp the concept here. Note the wording in the documentation. It states that the tick handler is called every n native execution cycles. That means native instructions, not including system calls (i'm guessing). This can give you a very good idea if you need to optimize a particular part of your script, since you can measure quite effectively how many native instructions are in your actual code.

A good profiler would take that into account, and force you, the developer, to include calls to the profiler as you're entering and leaving every function. That way you'd be able to keep an eye on how many cycles it took each function to complete. Independent of time.

That is extremely powerful, and not to be underestimated. A good solution would allow aggregate stats, so the total time in a function would be counted, including inside called functions.
up
19
Kubo2
4 years ago
Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.
up
17
sawyerrken at gmail dot com
6 years ago
In the following example:

<?php
function handler(){
    print
"hello <br />";
}

register_tick_function("handler");

declare(
ticks = 1){
   
$b = 2;
}
//closing curly bracket tickable
?>

"Hello" will be displayed twice because the closing curly bracket is also tickable.

One may wonder why the opening curly bracket is not tickable if the closing is tickable. This is because the instruction for PHP to start ticking is given by the opening curly bracket so the ticking starts immediately after it.
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2
digitalaudiorock at gmail dot com
5 months ago
A few important things to note for anyone using this in conjunction with signal handlers:

If anyone is trying to optionally use either pcntl_async_signals() when available (PHP >= 7.1) or ticks for older versions, this is not possible...at least not in a way that does NOT enable ticks for newer PHP versions. This is because there is simply no way to conditionally declare ticks. For example, the following will "work" but not in the way you might expect:

<?php
if (function_exists('pcntl_async_signals')) {
   
pcntl_async_signals(true);
} else {
    declare(
ticks=1);
}
?>

While signal handlers will work with this for old and new version, ticks WILL be enabled even in the case where pcntl_async_signals exists, simply because the declare statement exists. So the above is functionally equivalent to:

<?php
if (function_exists('pcntl_async_signals')) pcntl_async_signals(true);
declare(
ticks=1);
?>

Another thing to be aware of is that the scoping of this declaration changed a bit from PHP 5.6 to 7.x...actually it was corrected apparently as noted here:

http://php.net/manual/en/function.register-tick-function.php#121204

This can cause some very confusing behavior. One example is with the pear/System_Daemon module. With PHP 5.6 that will work with a SIGTERM handler even if the script using it doesn't itself use declare(ticks=1), but does not work in PHP 7 unless the script itself has the declaration. Not only does the handler not get called, but the signal does nothing at all, and the script doesn't exit.

A side note regarding ticks that's annoyed me for some time: As if there wasn't enough confusion around all this, the Internet is full of false rumors that ticks were deprecated and are being removed, and I believe they all started here:

http://www.hackingwithphp.com/4/21/0/the-declare-function-and-ticks

Despite a very obscure author's note at the very end of the page saying he got that wrong (that even I just noticed), the first very prominent sentence of the article still says this, and that page is near the top of any Google search.
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4
php dot net at e-z dot name
5 years ago
you can register multiple tick functions:

<?PHP
function a() { echo "a\n"; }
function
b() { echo "b\n"; }

register_tick_function('a');
register_tick_function('b');
register_tick_function('b');
register_tick_function('b');

?>

will output on every tick:
a
b
b
b
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3
fok at nho dot com dot br
16 years ago
This is a very simple example using ticks to execute a external script to show rx/tx data from the server

<?php

function traf(){
 
passthru( './traf.sh' );
  echo
"<br />\n";
 
flush(); // keeps it flowing to the browser...
 
sleep( 1 );
}

register_tick_function( "traf" );

declare(
ticks=1 ){
  while(
true ){}   // to keep it running...
}

?>

contents of traf.sh:
# Shows TX/RX for eth0 over 1sec
#!/bin/bash

TX1=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $9}'`
RX1=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $1}'`
sleep 1
TX2=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $9}'`
RX2=`cat /proc/net/dev | grep "eth0" | cut -d: -f2 | awk '{print $1}'`

echo -e "TX: $[ $TX2 - $TX1 ] bytes/s \t RX: $[ $RX2 - $RX1 ] bytes/s"
#--= the end. =--
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3
markandrewslade at dontspamemeat dot gmail
10 years ago
Note that the two methods for calling declare are not identical.

Method 1:

<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($str = '') {
    list(
$sec, $usec) = explode(' ', microtime());
   
printf("[%.4f] Tick.%s\n", $sec + $usec, $str);
}
register_tick_function('do_tick');

// Tick once before declaring so we have a point of reference.
do_tick('--start--');

// Method 1
declare(ticks=1);
while(
1) sleep(1);

/* Output:
[1234544435.7160] Tick.--start--
[1234544435.7161] Tick.
[1234544435.7162] Tick.
[1234544436.7163] Tick.
[1234544437.7166] Tick.
*/

?>

Method 2:
<?php
// Print "tick" with a timestamp and optional suffix.
function do_tick($str = '') {
    list(
$sec, $usec) = explode(' ', microtime());
   
printf("[%.4f] Tick.%s\n", $sec + $usec, $str);
}
register_tick_function('do_tick');

// Tick once before declaring so we have a point of reference.
do_tick('--start--');

// Method 2
declare(ticks=1) {
    while(
1) sleep(1);
}

/* Output:
[1234544471.6486] Tick.--start--
[1234544472.6489] Tick.
[1234544473.6490] Tick.
[1234544474.6492] Tick.
[1234544475.6493] Tick.
*/
?>

Notice that when using {} after declare, do_tick wasn't auto-called until about 1 second after we entered the declare {} block.  However when not using the {}, do_tick was auto-called not once but twice immediately after calling declare();.

I'm assuming this is due to how PHP handles ticking internally.  That is, declare() without the {} seems to trigger more low-level instructions which in turn fires tick a few times (if ticks=1) in the act of declaring.
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1
ohcc at 163 dot com
1 year ago
Using a directive that is not supported by current version of PHP will generate a warning like:

Warning: Unsupported declare 'strict_types' in D:\Server\wuxiancheng.cn\index.php on line 2

You CAN'T prepend an @ sign to the declare construct to supress that error message.

@declare(strict_types=1);

The above code will lead to a Parse error like:

Parse error: syntax error, unexpected 'declare' (T_DECLARE) in D:\Server\wuxiancheng.cn\index.php on line 2
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1
digitalaudiorock at gmail dot com
5 months ago
Regarding my previous comment as to the change in scope of declare(ticks=1) between 5.6 and 7.x, I intended to mention another example of the affect this can have on signal handlers:

If your script uses declare(ticks=1) and assigns handlers, in 5.6 signals will get caught and call the handler even when the code that is running is in an included file (where the included file doesn't have the declaration). However in 7.x the signal wouldn't get caught until the code returns to the main script.

The best solution to that is to use pcntl_async_signals(true) when it's available, which will allow the signals to get caught regardless of what file the code happens to be in.
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0
ja2016 at wir dot pl
1 year ago
Don't use uft-8 encoding with BOM. Then fatal error occurs ALWAYS. Substitute it with utf-8 without BOM.

---

*BOM*
<?php
declare(strict_types=1);
//Fatal error: strict_types declaration must be the very first statement in the script
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0
wapmorgan at gmail dot com
2 years ago
If you fork'ed (with pcntl_fork) after you've used `declare`, you need to do it again in child thread.

declare(ticks=1);
$pid = pcntl_fork();
if ($pid === 0) {
    declare(ticks=1);
} else {
    // code ..
}
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0
aeolianmeson at NOSPAM dot blitzeclipse dot com
13 years ago
The scope of the declare() call if used without a block is a little unpredictable, in my experience. It appears that if placed in a method or function, it may not apply to the calls that ensue, like the following:

<?php
function a()
{
   declare(
ticks=2);
  
b();
}

function
b()
{
  
// The declare may not apply here, sometimes.
}
?>

So, if all of a sudden the signals are getting ignored, check this. At the risk of losing the ability to make a mathematical science out of placing a number of activities at varying durations of ticks like many people have chosen to do, I've found it simple to just put this at the top of the code, and just make it global.
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-1
php at niekbosch dot nl
5 years ago
Basically 'declare( encoding = .... );' overrides the zend.script_encoding configuration option (as set in php.ini). However, keep in mind that:

* the file encoding must be compatible (at least in the ASCII range of characters) to the zend.script_encoding setting. If you set 'zend.script_encoding' to UTF-8 and save the file in UTF-16, PHP will not be able to interpret the file, let alone the declare statement. As long as you use ASCII compatible encodings (i.e. ISO-8859-1(5), UTF-8 etc) for both the file encoding as the zend.script_encoding, you should be fine. (However, I have not experimented with adding non-ascii characters in comments above the declare statement).

* PHP string literals are converted from your source code encoding (either set with the declare statement or else according to zend.script_encoding) to the mbstring.internal_encoding as set in your php.ini (even if you change the setting using mb_internal_encoding). As an example:

php.ini:
mbstring.internal_encoding = UTF-8

test.php:
<?php
declare(encoding = 'ISO-8859-15');
mb_internal_encoding( 'ISO-8859-15' );
echo
'aäaß' . "\n";
?>

This will still output the string UTF-8 encoded; in a terminal/browser with encoding 'ISO-8859-15' the string will look (something) like this: aÀaß
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-2
Ionut
2 years ago
I haven't found this written in the doc: when using declare in the global context, it has to be the first statement in the script, before any other output.

This works:

<?php
declare(strict_types=1);
function
sum(int $a, int $b): int {
    return
5.78;
}
# ... but fails when calling the function
?>

This doesn't work:

<html>
<body>
<?php
declare(strict_types=1);
function
sum(int $a, int $b): int {
    return
5.78;
}
# PHP Fatal error:  strict_types declaration must be the very first statement in the script [...]
?>
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