004PHP_ Comments - Manual

7/28/2019 004PHP_ Comments - Manual

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[edit] Last updated: Fri, 20 Apr 2012

Comments

PHP supports 'C', 'C++' and Uni x shell-style (Perl style) comments. F or example:

The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code

after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that. If the asp_tags

configuration directive is enabled, it behaves the same with // %> and # %>. However, the tag doesn't break out of PHP mode in a one-line

comment.

This is an example

The header above will say 'This is an example'.

'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to

comment out a large block of code.

User Contributed Notes Comments

team at researchbib dot com 13-Sep-2011 07:25

PHP: Comments - Manual http://www.php.net/manual/en/language.basic-syntax.comments.php

1 of 8 26/04/2012 11:03


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1 of 8 26/04/2012 11:03

when the comment string contains '?>', you should be careful.

e.g. output code 1= code 2 is different with code 3

1. with //

2. with #

3. with /* */

philip-php at dago dot yourweb dot de 05-Mar-2011 10:29

It's true, comments do not take up PROCESSING time, but they do take some PARSING time in case you are not using a compile cache of some

kind.

jballard at natoga dot com 15-Dec-2010 02:28

Comments do NOT take up processing power.

So, for all the people who argue that comments are undesired because they take up processing power now have no reason to comment ;)


3/8

echo microtime(), "
"; // 0.25163600 1292450508

echo microtime(), "
"; // 0.25186000 1292450508

// Test

echo microtime(), "
"; // 0.25189700 1292450508

# TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST

# .. Above comment repeated 18809 times ..

echo microtime(), "
"; // 0.25192100 1292450508

?>

They take up about the same amount of time (about meaning on a repeated testing, sometimes the difference between the control and the test

was negative and sometimes positive).

benny at bennyborn dot de 08-Dec-2010 03:16

This regex should do the job when trying to parse comments

(\/\*(.*?)\*\/)|(^|\s+)\/\/(.*?)(\n|$)|( |\s+)#(.*?)(\n|$)

Wolfsbay at ya dot ru 12-May-2010 02:10

If you are using editor with code highlight, its much easier to notice error like /* */ */.

theblazingangel at aol dot com 28-Aug-2007 03:55

it's perhaps not obvious to some, but the following code will cause a parse error! the ?> in //?> is not treated as commented text, this is

a result of having to handle code on one line such as

}

?>

i discovered this "anomally" when i commented out a line of code containing a regex which itself contained ?>, with the // style comment.

e.g. //preg_match('/^(?>c|b)at$/', 'cat', $matches);

will cause an error while commented! using /**/ style comments provides a solution. i don't know about # style comments, i don't ever

personally use them.

fun at nybbles dot com 13-Jul-2006 10:28


3 of 8 26/04/2012 11:03


4/8

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:

and then deeper inside the file:


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*/

//echo "";

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

?>

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 25-May-2006 11:39

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 01:46

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 11-Nov-2005 08:30

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


5 of 8 26/04/2012 11:03PHP C M l h // h / l/ /l b i h


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}

// */

sort($morecode);

?>

..the block is suddenly commented out.

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

vs

Steve 15-Dec-2004 04:41

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 ;-)

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