declare

(PHP 4, PHP 5, PHP 7)

The declare construct is used to set execution directives for a block of code. The syntax of declare is similar to the syntax of other flow control constructs:

declare (directive)
    statement

The directive section allows the behavior of the declare block to be set. Currently only three directives are recognized: the ticks directive (See below for more information on the ticks directive), the encoding directive (See below for more information on the encoding directive) and the strict_types directive (See for more information the strict section on the Function arguments page)

Version Description
5.3.0 Added encoding directive
7.0.0 Added strict_types directive

As directives are handled as the file is being compiled, only literals may be given as directive values. Variables and constants cannot be used. To illustrate:

<?php
// This is valid:
declare(ticks=1);

// This is invalid:
const TICK_VALUE 1;
declare(
ticks=TICK_VALUE);
?>

The statement part of the declare block will be executed - how it is executed and what side effects occur during execution may depend on the directive set in the directive block.

The declare construct can also be used in the global scope, affecting all code following it (however if the file with declare was included then it does not affect the parent file).

<?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

A tick is an event that occurs for every N low-level tickable statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare block's directive section.

Not all statements are tickable. Typically, condition expressions and argument expressions are not tickable.

The event(s) that occur on each tick are specified using the register_tick_function(). See the example below for more details. Note that more than one event can occur for each tick.

Example #1 Tick usage example

<?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);
}

?>

Example #2 Ticks usage example

<?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();

?>

See also register_tick_function() and unregister_tick_function().

Encoding

A script's encoding can be specified per-script using the encoding directive.

Example #3 Declaring an encoding for the script.

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

Caution

When combined with namespaces, the only legal syntax for declare is declare(encoding='...'); where ... is the encoding value. declare(encoding='...') {} will result in a parse error when combined with namespaces.

The encoding declare value is ignored in PHP 5.3 unless php is compiled with --enable-zend-multibyte.

Note that PHP does not expose whether --enable-zend-multibyte was used to compile PHP other than by phpinfo().

See also zend.script_encoding.

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User Contributed Notes 12 notes

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29
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
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
13
Kubo2
3 years ago
Note that in PHP 7 <?php declare(encoding='...'); ?> throws an E_WARNING if Zend Multibyte is turned off.
up
4
php dot net at e-z dot name
5 years ago
you can register multiple tick functions