注释

PHP 支持 C，C++ 和 Unix Shell 风格（Perl 风格）的注释。例如:


<?php
    echo "This is a test"; // This is a one-line c++ style comment
    /* This is a multi line comment
       yet another line of comment */
    echo "This is yet another test";
    echo "One Final Test"; # This is shell-style style comment
?>

单行注释仅仅注释到行末或者当前的 PHP 代码块，视乎哪个首先出现。这意味着在 // ?> 之后的 HTML 代码将被显示出来：?> 跳出了 PHP 模式并返回了 HTML 模式，// 并不能影响到这一点。如果启用了 asp_tags 配置选项，其行为和 // %> 相同。不过，</script> 标记在单行注释中不会跳出 PHP 模式。


<h1>This is an <?php # echo "simple";?> example.</h1>
<p>The header above will say 'This is an example'.

C 风格的注释在碰到第一个 */ 时结束。小心不要嵌套 C 风格的注释，当注释大量代码时，可能犯该错误。


<?php
 /*
    echo "This is a test"; /* This comment will cause a problem */
 */
?>

add a note User Contributed Notes

fun at nybbles dot com
14-Jul-2006 01:28


a trick I have used in all languages to temporarily block out large sections (usually for test/debug/new-feature purposes), is to set (or define) a var at the top, and use that to conditionally comment the blocks; an added benefit over if(0) (samuli's comment from nov'05) is that u can have several versions or tests running at once, and u dont require cleanup later if u want to keep the blocks in:  just reset the var.



personally, I use this more to conditionally include code for new feature testing, than to block it out,,,, but hey, to each their own :)



this is also the only safe way I know of to easily nest comments in any language, and great for multi-file use, if the conditional variables are placed in an include :)



for example, placed at top of file:



<?php $ver3 = TRUE;  

       $debug2 = FALSE; 

?> 



and then deeper inside the file: 



<?php if ($ver3) {

           print("This code is included since we are testing version 3");

         }

?>



<?php if ($debug2) {

           print("This code is 'commented' out");

         }

?>

mst_NO_SPAM_TO_ME at mstsoft dot com
05-Jun-2006 08:38


This "comment ends on line break or end of PHP Block" thing can be confusing. I discovered this by accident when working with XML Output from PHP...



<?PHP



header("Content-type: text/xml");



/*

echo "<?xml version=\"1.0\"?>";

echo "<page>multi-line comments work as expected.</page>";

*/



//echo "<?xml version=\"1.0\"?>";

//echo "<page>single-line comments end php mode and output your code.</page>";



?>



I would expect the comment to work, but there is no parsing in comments so the String suddenly becomes a PHP  end-block tag, which is correct reading this documentation.



cheers,

martin

PS: You even see the behavior in the Syntax highlighting :-)

J Lee
26-May-2006 02:39


MSpreij (8-May-2005) says  /* .. */ overrides //  

Anonymous (26-Jan-2006) says // overrides /* .. */



Actually, both are correct. Once a comment is opened, *everything* is ignored until the end of the comment (or the end of the php block) is reached.



Thus, if a comment is opened with: 

   //  then /* and */ are "overridden" until after end-of-line 

   /*  then // is "overridden" until after */

21-Jan-2006 05:46


M Spreij wrote, 08-May-2005 08:15...

A nice way to toggle the commenting of blocks of code can be done by mixing the two comment styles:

...

This works because a /* .. */ overrides //. 



The final sentence should be the other way round, i.e.



This works because a // overrides /* .. */. 

(If it didn't the /* .. */ would comment out the code regardless of whether an additional '/' is prefixed to the first line).

samuli dot karevaara at lamk dot fi
12-Nov-2005 12:30


If you want to comment out large sections of code (temporarily, usually and hopefully), consider using

<?php

if (0) {

     print("This code is 'commented' out");

}

?>

instead of /* comment block */. Otherwise, as noted here, you will have parse errors if the block that you commented out contains */ somewhere, like in regexp or in another comment.

hcderaad at wanadoo dot nl
30-Jun-2005 04:51


Comments in PHP can be used for several purposes, a very interesting one being that you can generate API documentation directly from them by using PHPDocumentor (http://www.phpdoc.org/).



Therefor one has to use a JavaDoc-like comment syntax (conforms to the DocBook DTD), example:

<?php

/**

* The second * here opens the DocBook commentblock, which could later on<br>

* in your development cycle save you a lot of time by preventing you having to rewrite<br>

* major documentation parts to generate some usable form of documentation.

*/

?>

Some basic html-like formatting is supported with this (ie <br> tags) to create something of a layout.

M Spreij
09-May-2005 03:15


A nice way to toggle the commenting of blocks of code can be done by mixing the two comment styles:

<?php

//*

if ($foo) {

  echo $bar;

}

// */

sort($morecode);

?>



Now by taking out one / on the first line..



<?php

/*

if ($foo) {

  echo $bar;

}

// */

sort($morecode);

?>

..the block is suddenly commented out.

This works because a /* .. */ overrides //. You can even "flip" two blocks, like this:

<?php

//*

if ($foo) {

  echo $bar;

}

/*/

if ($bar) {

  echo $foo;

}

// */

?>

vs

<?php

/*

if ($foo) {

  echo $bar;

}

/*/

if ($bar) {

  echo $foo;

}

// */

?>

Steve
15-Dec-2004 08:41


Be careful when commenting out regular expressions.



E.g. the following causes a parser error.



I do prefer using # as regexp delimiter anyway so it won't hurt me ;-)



<?php 



/*



 $f->setPattern('/^\d.*/');



*/



?>

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