Руководство по PHP
Пред. | Глава 16. Control Structures | След.

# `declare`

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 one directive is recognized: the `ticks` directive. (See below for more information on the ticks directive)

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.

`<?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 statements executed by the parser within the `declare` block. The value for `N` is specified using `ticks=`N`` within the `declare` blocks's `directive` section.

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.

Пример 16-3. Profile a section of PHP code

`<?php
// A function that records the time when it is called
function profile($dump = FALSE)
{
static $profile;
// Return the times stored in profile, then erase it
if ($dump) {
$temp = $profile;
unset($profile);
return $temp;
}
$profile[] = microtime();
}
// Set up a tick handler
register_tick_function("profile");
// Initialize the function before the declare block
profile();
// Run a block of code, throw a tick every 2nd statement
declare(ticks=2) {
for ($x = 1; $x < 50; ++$x) {
echo similar_text(md5($x), md5($x*$x)), "<br />;";
}
}
// Display the data stored in the profiler
print_r(profile(TRUE));
?>`

The example profiles the PHP code within the 'declare' block, recording the time at which every second low-level statement in the block was executed. This information can then be used to find the slow areas within particular segments of code. This process can be performed using other methods: using ticks is more convenient and easier to implement.

Ticks are well suited for debugging, implementing simple multitasking, background I/O and many other tasks.

See also register_tick_function() and unregister_tick_function().

Пред. | Начало | След.
`switch` | Уровень выше | return