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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 |
|---|---|
| 7.0.0 | Added strict_types directive |
| 7.0.0 | The ticks directive does no longer leak into different compilation units. |
| 5.3.0 | Added encoding 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
?>
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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Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-control-structures.declare.html
The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.
References
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