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>Hoofdstuk 11. Control Structures</TD
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><H1
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><A
NAME="control-structures.declare"
><VAR
CLASS="literal"
>declare</VAR
></A
></H1
><P
> The <VAR
CLASS="literal"
>declare</VAR
> construct is used to is
used to set execution directives for a block of code.
The syntax of <VAR
CLASS="literal"
>declare</VAR
> is similiar to
the syntax of other flow control constructs:
<DIV
CLASS="informalexample"
><P
></P
><A
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></A
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><TD
><PRE
CLASS="programlisting"
>declare (directive) statement</PRE
></TD
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></TABLE
><P
></P
></DIV
>
</P
><P
> The <VAR
CLASS="literal"
>directive</VAR
> section allows the
behavior of the <VAR
CLASS="literal"
>declare</VAR
> block to
be set.
Currently only one directive is recognized: the
<VAR
CLASS="literal"
>ticks</VAR
> directive. (See below for more
information on the
<A
HREF="control-structures.declare.html#control-structures.declare.ticks"
>ticks</A
>
directive)
</P
><P
> The <VAR
CLASS="literal"
>statement</VAR
> part of the
<VAR
CLASS="literal"
>declare</VAR
> block will be executed - how
it is executed and what side-effects occur during execution
may depend on the directive set in the
<VAR
CLASS="literal"
>directive</VAR
> block.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="control-structures.declare.ticks"
>Ticks</A
></H2
><P
>A tick is an event that occurs for every
<VAR
CLASS="replaceable"
>N</VAR
> low-level statements executed
by the parser within the <VAR
CLASS="literal"
>declare</VAR
> block.
The value for <VAR
CLASS="replaceable"
>N</VAR
> is specified
using <VAR
CLASS="literal"
>ticks=<VAR
CLASS="replaceable"
>N</VAR
></VAR
>
within the <VAR
CLASS="literal"
>declare</VAR
> blocks's
<VAR
CLASS="literal"
>directive</VAR
> section.
</P
><P
> The event(s) that occurs on each tick is specified using the
<A
HREF="function.register-tick-function.html"
><B
CLASS="function"
>register_tick_function()</B
></A
>. See the example
below for more details. Note that more than one event can occur
for each tick.
</P
><P
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><DIV
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><A
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></A
><P
><B
>Voorbeeld 11-1. Profile a section of PHP code</B
></P
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><code><font color="#000000">
<pre><br /><font color="#0000BB"><?php<br /></font><font color="#FF8000">// A function that records the time when it is called<br /></font><font color="#007700">function </font><font color="#0000BB">profile </font><font color="#007700">(</font><font color="#0000BB">$dump </font><font color="#007700">= </font><font color="#0000BB">FALSE</font><font color="#007700">)<br />{<br /> static </font><font color="#0000BB">$profile</font><font color="#007700">;<br /><br /> </font><font color="#FF8000">// Return the times stored in profile, then erase it<br /> </font><font color="#007700">if (</font><font color="#0000BB">$dump</font><font color="#007700">) {<br /> </font><font color="#0000BB">$temp </font><font color="#007700">= </font><font color="#0000BB">$profile</font><font color="#007700">;<br /> unset (</font><font color="#0000BB">$profile</font><font color="#007700">);<br /> return (</font><font color="#0000BB">$temp</font><font color="#007700">);<br /> }<br /><br /> </font><font color="#0000BB">$profile</font><font color="#007700">[] = </font><font color="#0000BB">microtime </font><font color="#007700">();<br />}<br /><br /></font><font color="#FF8000">// Set up a tick handler<br /></font><font color="#0000BB">register_tick_function</font><font color="#007700">(</font><font color="#DD0000">"profile"</font><font color="#007700">);<br /><br /></font><font color="#FF8000">// Initialize the function before the declare block<br /></font><font color="#0000BB">profile </font><font color="#007700">();<br /><br /></font><font color="#FF8000">// Run a block of code, throw a tick every 2nd statement<br /></font><font color="#007700">declare (</font><font color="#0000BB">ticks</font><font color="#007700">=</font><font color="#0000BB">2</font><font color="#007700">) {<br /> for (</font><font color="#0000BB">$x </font><font color="#007700">= </font><font color="#0000BB">1</font><font color="#007700">; </font><font color="#0000BB">$x </font><font color="#007700">< </font><font color="#0000BB">50</font><font color="#007700">; ++</font><font color="#0000BB">$x</font><font color="#007700">) {<br /> echo </font><font color="#0000BB">similar_text </font><font color="#007700">(</font><font color="#0000BB">md5</font><font color="#007700">(</font><font color="#0000BB">$x</font><font color="#007700">), </font><font color="#0000BB">md5</font><font color="#007700">(</font><font color="#0000BB">$x</font><font color="#007700">*</font><font color="#0000BB">$x</font><font color="#007700">)), </font><font color="#DD0000">"<br>"</font><font color="#007700">;<br /> }<br />}<br /><br /></font><font color="#FF8000">// Display the data stored in the profiler<br /></font><font color="#0000BB">print_r </font><font color="#007700">(</font><font color="#0000BB">profile </font><font color="#007700">(</font><font color="#0000BB">TRUE</font><font color="#007700">));<br /></font><font color="#0000BB">?><br /></font></pre></font>
</code></TD
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>
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.
</P
><P
> Ticks are well suited for debugging, implementing simple
multitasking, backgrounded I/O and many other tasks.
</P
><P
> See also <A
HREF="function.register-tick-function.html"
><B
CLASS="function"
>register_tick_function()</B
></A
> and
<A
HREF="function.unregister-tick-function.html"
><B
CLASS="function"
>unregister_tick_function()</B
></A
>.
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