declare

(PHP 4, PHP 5, PHP 7)

declare 文は、あるコードブロックの中に 実行ディレクティブをセットするために使用されます。declare の文法は他の制御構造と似ています。

declare (ディレクティブ)
    文

ディレクティブの箇所で、セットされた declareブロックの挙動を指定することが出来ます。 現在のところ、使用できるディレクティブは ticks ( ticksに関しては以下を参照してください)、 encoding (encoding に関しては以下を参照ください)、 strict_types (strict に関しては関数の引数のページを参照ください) です。

バージョン 説明
5.3.0 encoding ディレクティブが追加されました。
7.0.0 strict_types ディレクティブが追加されました。

ディレクティブの処理は、ファイルをコンパイルする際に行われるので、 ディレクティブの値として渡せるのは、リテラルだけとなります。 変数や定数は、使えません。以下に例を示します。

<?php
// これは有効です
declare(ticks=1);

// これは無効です
const TICK_VALUE 1;
declare(
ticks=TICK_VALUE);
?>

declareブロックの の実行のされ方や実行時にどのような作用が起こるかについては ディレクティブに何が指定されたかに依存します。

declare構造はグローバルスコープしても使用され、 それはそれ以降のコード上の全てにおいて影響します (しかし、declare を含むファイルがインクルードされた場合は、 親ファイルにはその影響は及びません)。

<?php
// 以下は同じ意味です

// こうすることもできますし、
declare(ticks=1) {
    
// ここにすべてのスクリプトを書きます
}

// こうすることもできます
declare(ticks=1);
// ここにすべてのスクリプトを書きます
?>

Ticks

tickとはdeclareブロックの実行中にパーサが N個の低レベル tick 可能な文を実行するごとに 発生するイベントのことです。Nの値は declareブロックのディレクティブの箇所で ticks=Nのように 指定します。

すべての文が tick 可能なわけではありません。 たとえば条件式や引数式などは tick できません。

tickごとに発生させるイベントはregister_tick_function() を使用して指定します。詳細は以下の例を参照してください。1回のtickで 複数のイベントが起こり得ることに注意してください。

例1 Tick の使用例

<?php

declare(ticks=1);

// tick イベントごとにコールされる関数
function tick_handler()
{
    echo 
"tick_handler() called\n";
}

register_tick_function('tick_handler');

$a 1;

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

?>

例2 Ticks の使用例

<?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();

?>

register_tick_function() および unregister_tick_function() も参照ください。

Encoding

スクリプトのエンコーディングをスクリプトごとに指定するには encoding ディレクティブを使用します。

例3 スクリプトのエンコーディングの宣言

<?php
declare(encoding='ISO-8859-1');
// ここにコードを書きます
?>

警告

名前空間と組み合わせて使用する場合、使用できる形式は declare(encoding='...'); のみです。... にエンコーディングを指定します。declare(encoding='...') {} は、名前空間と組み合わせるとパースエラーとなります。

php を --enable-zend-multibyte つきでコンパイルしていない場合、 PHP 5.3 では encoding 宣言は無視されます。

PHP が --enable-zend-multibyte つきでコンパイルされているかどうかを知る方法は phpinfo() 以外に存在しないことに注意しましょう。

zend.script_encoding も参照ください。

add a note add a note

User Contributed Notes 14 notes

up
34
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
18
Kubo2
4 years ago
Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.
up
18
sawyerrken at gmail dot com
5 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
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
up
4
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.
up
3
fok at nho dot com dot br
15 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
1
digitalaudiorock at gmail dot com
1 month 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.
up
0
digitalaudiorock at gmail dot com
1 month 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.
up
0
ohcc at 163 dot com
10 months 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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0
wapmorgan at gmail dot com
1 year 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 ..
}
up
0
aeolianmeson at NOSPAM dot blitzeclipse dot com
12 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
up
-1
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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-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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