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 ?>
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.
Example 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.
Php control structures.declare Function syntax tag
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Php control structures.declare syntax tutorial
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