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return> <switch
[edit] Last updated: Fri, 23 Mar 2012

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declare

declare yapısı bir kod bloğunun çalıştırılması esnasında uygulanacak yönergeleri belirlemek için kullanılır. declare yapısının sözdizimi diğer akış denetim yapılarının söz dizimi ile benzerdir: 

declare (yönerge)
    deyim

yönerge bölümü, declare bloğunun davranışını belirlemek için kullanılır. Şimdilik yalnızca iki yönerge kullanılabilmektedir: ticks yönergesi (Daha fazla bilgi edinmek için aşağıya, ticks yönergesine bakınız.) ve encoding yönergesi.

Bilginize: encoding yönergesi PHP 5.3.0'da eklenmiştir.

declare bloğunun deyim bölümünün nasıl çalıştırılacağı ve çalışma esnasındaki yan etkilerinin ne olacağı yönerge bölümünde belirtilen yönergeye bağlı olabilir.

declare bloğu kendinden sonra gelen tüm kodu etkilemesi için genel betik kapsamında da kullanılabilir. Bununla birlikte, declare bloğu dahil edilen bir dosyanın içindeyse ebeveyn dosya bundan etkilenmez.

<?php
// aşağıdaki iki örnek aynıdır:

// bunu kullanabilirsiniz:
declare(ticks=1) {
    // betiğin tamamı burada
}

// ya da bunu kullanabilirsiniz:
declare(ticks=1);
    // betiğin tamamı burada
?>

Tikler

Bir "tik", declare bloğu içersinde çözümleyici tarafından çalıştırılan her N tiklenebilir deyimde bir ortaya çıkan bir olaydır. N değeri, declare bloğunun yönerge bölümünde ticks=N kullanılarak belirtilir.

Her deyim tik sayımına dahil edilebilir değildir. Koşullu ifadeler ve değiştirge ifadeleri bu tür deyimlerdendir.

Her tik ile oluşturulacak eylem register_tick_function() işlevi ile belirtilir. Daha ayrıntılı bilgi için aşağıdaki örneğe bakınız. Her tik için birden fazla olayın oluşabileceğini gözardı etmeyiniz.

Örnek 1 - Tik kullanım örneği 1

<?php

declare(ticks=1);

// Her tik deyimde bir çalıştırılacak işlev
function tik_eylemci()
{
    echo "tik_eylemci() çağrıldı\n" ;
}

// Tik eylemcisini belirtelim
register_tick_function("tik_eylemci");

$a = 1;

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

Örnek 2 - Tik kullanım örneği 2

<?php

function tik_eylemci()
{
    echo "tik_eylemci() çağrıldı\n" ;
}

$a = 1;
tik_eylemci();

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

?>

Ayrıca, register_tick_function() ve unregister_tick_function() işlevlerini de inceleyin.

encoding

Her betiğin karakter kodlaması betiğin başında encoding yönergesi ile belirtilebilir.

Örnek 3 - Betik için kodlama belirtmek

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

Dikkat

İsim alanları ile birlikte kullanıldığında, tek geçerli sözdizimi declare(encoding='...'); olup, buradaki ... kodlama değeridir. declare(encoding='...') {} sözdizimi isim alanları ile birlikte kullanıldığında bir çözümleme hatası ile sonuçlanacaktır.

Karakter kodlaması bildirim değeri, PHP, --enable-zend-multibyte yapılandırma seçeneği ile derlenmediği takdirde PHP 5.3'te yoksayılır. PHP 6.0'da --enable-zend-multibyte etkindir.



return> <switch
[edit] Last updated: Fri, 23 Mar 2012
 
add a note add a note User Contributed Notes declare
Tom Samplonius 01-Apr-2011 03:02
The tick handler is intended for code profiling.  You can use it to determine the number of time units (ticks) that a chunk of code takes.  And you can vary the tick frequency so profiling doesn't impact your specific code too much.  A tick handler can gather other useful performance data, besides just counting ticks.

You can use the tick handler to poll that your connection is a alive, but this will block your entire script.  Polling connection status is no substitute for checking return values, and using timeouts on any function that connects to an external system.
ramamneh at gmail dot com 19-Dec-2010 11:15
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 ;
}
?>
Anonymous 27-Sep-2010 02:10
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.
markandrewslade at dontspamemeat dot gmail 13-Feb-2009 09:06
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.
anotheruser at example dot com 23-Aug-2008 04:50
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

?>
zabmilenko at charter dot net 08-Jan-2008 01:49
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
rsemil at gmail dot com 06-Jan-2008 06:30
rosen_ivanov's solution can be replaced by a simple call to memory_get_peak_usage() if you're running at least PHP 5.2.0
rosen_ivanov at abv dot bg 28-Aug-2006 06:06
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 :)
aeolianmeson at NOSPAM dot blitzeclipse dot com 30-May-2006 12:06
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.
warhog at warhog dot net 18-Dec-2005 12:39
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
}

?>
chris-at-free-source.com 28-Feb-2005 12:16
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.
fok at nho dot com dot br 07-Jul-2003 06:45
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. =--
daniel@swn 01-Feb-2003 11:56
<?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); }
xxoes 08-Jan-2003 02:23
If i use ticks i must declare all functions before i call the function.

example:

Dosn't work
<?php
function ticks() {
   echo "tick";
}
register_tick_function("ticks");

declare (ticks=1) 1;

echo "";
echo "";

foo(); // Call to undefined function.

function foo() {
   echo "foo";
}
?>

Work
<?php
function ticks() {
   echo "tick";
}
register_tick_function("ticks");

//declare (ticks=1) 1;

echo "";
echo "";

foo();

function foo() {
   echo "foo";
}
?>

win2k : PHP 4.3.0 (cgi-fcgi)
rob_spamsux at rauchmedien dot ihatespam dot com 19-Mar-2002 02:45
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.
rob_spamsux at rauchmedien dot ihatespam dot com 19-Mar-2002 01:58
Here is an example of multi-tasking / multi-threading:

<?php
# declare functions
function a() {
  echo "a";
}
function b() {
  echo "b";
}

# register tick functions
register_tick_function ("a");
register_tick_function ("b");

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

# that's all there is to it.
?>

Notes:
This will make functions a and b run once each at the same time.

If you try:

declare (ticks=1) {
  1;
}

They will run twice each. That is because it seems to be an undocumented fact that there is always an extra tick.

Therefore:

declare (ticks=2) {
  1;
}

Will cause them to run once.
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