PHP. Руководство по PHP. 2005

declare

Руководство по PHP

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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.