declare

(PHP 4, PHP 5, PHP 7, PHP 8)

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)

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
?>

<?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);
}

?>

<?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();

?>

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