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 20 notes

up
8
Kubo2
1 year ago
Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.
up
14
sawyerrken at gmail dot com
2 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.
up
11
Anonymous
5 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
8
markandrewslade at dontspamemeat dot gmail
7 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.
up
3
php dot net at e-z dot name
2 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
up
1
SteAp
1 month ago
This helper class traces executed statements. Calls it like so:

       CStatementTracer::getInstance()->enableTrace( 'START' );

Source Code

<?php

declare(ticks=1);

class
CStatementTracer {
   
    static private
       
$_instance;
       
    static
$lastMessage;
   
    static
$skipFunctionNames;
   
    protected function
__construct( ) {

       
self::$skipFunctionNames = array(
        );
           
    }
// CStatData

        /**
     * Liefert die Instanz zurück
     *
     * @return unknown
     */
   
static public function getInstance() {
       
       if (
self::$_instance === null ) {
           
self::$_instance = new CStatementTracer();
        }
        return
self::$_instance;
       
    }
   
    public function
addToSkipFunctionNames( $aName ) {
       
       
self::$skipFunctionNames[] = $aName;
       
    }
   
    public function
enableTrace() {
       
       
$this->writeMessage( '*************** START  ********************' );
       
       
register_tick_function( array( $this, 'traceCallback' ) );

    }
   
    public function
disableTrace() {

       
$this->writeMessage( 'STOP - ' );
       
       
unregister_tick_function( array( $this, 'traceCallback' ) );
       
       
    }

    public function
traceCallback( ) {
       
       
$trace = debug_backtrace();
       
       
$latestCall = $trace[ 1 ];
       
       
$shortenedArgs = array();
        foreach(
$latestCall['args'] as $noUseKey => $someArg ) {
           
            if (
is_object( $someArg ) ) {
               
$someArg = get_class( $someArg ) . '{}';
            } elseif (
is_array( $someArg ) ) {
               
$someArg = print_r( $someArg, TRUE );
            } elseif (
is_string( $someArg )) {
               
$someArg = '"' . $someArg . '"';
            }
           
           
$someArg = str_replace( "\n", ' ', $someArg );
           
$someArg = str_replace( "\r", ' ', $someArg );
           
$someArg = str_replace( "    ", ' ', $someArg );
           
$someArg = str_replace( "   ", ' ', $someArg );
           
$someArg = str_replace( "  ", ' ', $someArg );
           
            if (
80 < strlen( $someArg ) ) {
               
$someArg = substr( $someArg, 0, 15 ) . '...' . substr( $someArg, -15 );
            }
           
           
$shortenedArgs[] = $someArg;
           
        }

        if ( isset(
$latestCall['file'] )) {

           
$file = explode( '\\', $latestCall[ 'file' ] );
           
$file = $file[ count( $file ) - 1 ];
            if (
'' == $file ) {
               
$file = '{}';
            }
           
$file .= '/' . $latestCall[ 'line' ];

        } else {

           
$file = '[NpFile]';

        }
       
        if (  (
True === in_array( $latestCall['function'], self::$skipFunctionNames ) )
           ) {
            return;
        }
       
       
$args = implode( ', ', $shortenedArgs );
       
$newInfo = $file . ': ' . $latestCall['function'] . '( ' . $args . ' )';
       
       
$newInfo = str_pad( '', 2 * count( $trace ) ) . $newInfo;
       
       
$this->writeMessage( $newInfo );
    }

   
    public function
writeMessage( $someData ) {
       
        if (
self::$lastMessage == $someData ) {
            return;
        }
       
       
self::$lastMessage = $someData;
       
       
$logfilePath = dirname( __FILE__ ) . '/../statementTracer.log';
       
       
$fp = fopen( $logfilePath, 'a+' );
       
        if (
is_array( $someData ) ) {
           
fwrite( $fpprint_r( $someData, TRUE )  . "\n" );
        } else {
           
fwrite( $fp$someData  . "\n" );
        }
       
       
fclose( $fp );
    }  
    
   
}
// CStatementTracer
up
1
fok at nho dot com dot br
12 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. =--
up
0
zabmilenko at charter dot net
8 years ago
If you misspell the directive, you won't get any error or warning.  The declare block will simply act as a nest for statements:

<?php
declare(tocks="four hundred")
{
   
// Has no affect on code and produces
    // no error or warning.
}
?>

Tested in php 5.2.5 on XPsp2
up
-1
nospam dot narf at bofh dot bg
2 years ago
This manual doesn't say what "script's encoding" means and how declaring it affects its behavior.

Of course declare(encoding='foo') would specify the encoding - that's self-explanatory and not helpful.
up
-3
php at niekbosch dot nl
2 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
up
-3
aeolianmeson at NOSPAM dot blitzeclipse dot com
9 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.
up
-6
ramamneh at gmail dot com
5 years ago
check loaded server connection

<?php
$connection 
= false;
function
checkConnection( $connectionWaitingTime = 3 )
{
   
// check connection & time
   
global $time,$connection;
    if( (
$t = (time() - $time)) >= $waitingTime  && !$connection){ 
        echo (
"<p> Server not responding  for <strong>$t</strong> seconds !! </p>");
        die(
"Connection aborted");
           
    }
   
}

register_tick_function("checkConnection");
$time = time();
declare (
ticks=1)
{
    while(
true ){ // connecting to loaded server
   
}
   
$connection = true ;
}
?>
up
-4
danekilian at wp dot pl
1 year ago
We can specify different encoding to different blocks:

declare(encoding=ENCODING_VALUE) {
    //for a block
}

found this here:
http://code2care.org/tutorials/php/PHP-Declare-ticks-and-tick-functions-Statements-Tutorial.php
up
-10
Kamil Pawelkiewicz
3 years ago
I've created memory usage monitor class using tick event.

The result is returned in a fancy graph using GD library.

You can get the source, readme and example script at:
https://github.com/kampaw/profiler

Usage is very simple:

<?php
 
require('profiler.php');

 
$profiler = new profiler;
  declare(
ticks = 1000);

 
// monitor started
  // insert your code here

 
$profiler->chart();
?>
up
-5
daniel@swn
13 years ago
<?php
ob_end_clean
();
ob_implicit_flush(1);

function
a() {
for(
$i=0;$i<=100000;$i++) { }
echo
"function a() ";
}
function
b() {
for(
$i=0;$i<=100000;$i++) { }
echo
"function b() ";
}

register_tick_function ("a");
register_tick_function ("b");

declare (
ticks=4)
{
    while(
true)
    {
       
sleep(1);
        echo
"\n<br><b>".time()."</b><br>\n";;
    }
}
?>
You will see that a() and b() are slowing down this process. They are in fact not executed every second as expected. So this function is not a real alternative for multithreading using some slow functions..there is no difference to this way: while (true) { a(); b(); sleep(1); }
up
-8
anotheruser at example dot com
7 years ago
Code evaluation script which uses debug_backtrace() to get execution time in ns, relative current line number, function, file, and calling function info on each tick, and shove it all in $script_stats array.  See debug_backtrace manual to customize what info is collected.

Warning: this will exhaust allowed memory very easily, so adjust tick counter according to the size of your code.  Also, array_key_exists checking on debug_backtrace arrays is removed here only to keep this example simple, but should be added to avoid a large number of resulting PHP Notice errors.

<?php

$script_stats
= array();
$time = microtime(true);

function
track_stats(){
    global
$script_stats,$time;
   
$trace = debug_backtrace();
   
$exe_time = (microtime(true) - $time) * 1000;
   
$func_args = implode(", ",$trace[1]["args"]);
   
$script_stats[] = array(
       
"current_time" => microtime(true),
       
"memory" => memory_get_usage(true),
       
"file" => $trace[1]["file"].': '.$trace[1]["line"],
       
"function" => $trace[1]["function"].'('.$func_args.')',
       
"called_by" => $trace[2]["function"].' in '.$trace[2]["file"].': '.$trace[2]["line"],
       
"ns" => $exe_time
       
);
   
$time = microtime(true);
    }

declare(
ticks = 1);
register_tick_function("track_stats");

// the rest of your project code

// output $script_stats into a html table or something

?>
up
-7
warhog at warhog dot net
10 years ago
as i read about ticks the first time i thought "wtf, useless crap" - but then i discovered some usefull application...

you can declare a tick-function which checks each n executions of your script whether the connection is still alive or not, very usefull for some kind of scripts to decrease serverload

<?php

function check_connection()
{ if (
connection_aborted())
   {
// do something here, e.g. close database connections
      // (or  use a shutdown function for this
     
exit; }
}

register_tick_function("connection");

declare (
ticks=20)
{
 
// put your PHP-Script here
  // you may increase/decrease the number of ticks
}

?>
up
-7
chris-at-free-source.com
11 years ago
Also note that PHP is run in a single thread and so everything it does will be one line of code at a time.  I'm not aware of any true threading support in PHP, the closest you can get is to fork.

so, declare tick doens't "multi-thread" at all, it is simply is a way to automaticaly call a function every n-lines of code.
up
-7
rob_spamsux at rauchmedien dot ihatespam dot com
14 years ago
Correction to above note:

Apparently, the end brace '}' at the end of the statement causes a tick.

So using

------------
declare (ticks=1) echo "1 tick after this prints";
------------

gives the expected behavior of causing 1 tick.

Note: the tick is issued after the statement executes.

Also, after playing around with this, I found that it is not really the multi-tasking I had expected. It behaves the same as simply calling the functions. I.e. each function must finish before passing the baton to the next function. They do not run in parallel.

It also seems that they always run in the order in which they were registered.

So,

<?php
------------
# register tick functions
register_tick_function ("a");
register_tick_function ("b");

# make the tick functions run
declare (ticks=1);
?>
------------

is equivalent to

------------
a();
b();
------------

It is simply a convenient way to have functions called periodically while some other code is being executed. I.e. you could use it to periodically check the status of something and then exit the script or do something else based on the status.
up
-8
rosen_ivanov at abv dot bg
9 years ago
As Chris already noted, ticks doesn't make your script multi-threaded, but they are still great. I use them mainly for profiling - for example, placing the following at the very beginning of the script allows you to monitor its memory usage:

<?php

function profiler($return=false) {
    static
$m=0;
    if (
$return) return "$m bytes";
    if ((
$mem=memory_get_usage())>$m) $m = $mem;
}

register_tick_function('profiler');
declare(
ticks=1);

/*
Your code here
*/

echo profiler(true);

?>

This approach is more accurate than calling memory_get_usage only in the end of the script. It has some performance overhead though :)
To Top