Instruction separation
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 ($debug2) {
print("This code is 'commented' out");
}
?>
Comments
PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:
<?php
echo 'This is a test'; // This is a one-line c++ style comment
/* This is a multi line comment
yet another line of comment */
echo 'This is yet another test';
echo 'One Final Test'; # This is a one-line shell-style comment
?>
The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that. If the asp_tags configuration directive is enabled, it behaves the same with // %> and # %>. However, the </script> tag doesn't break out of PHP mode in a one-line comment.
<h1>This is an <?php # echo 'simple';?> example</h1>
<p>The header above will say 'This is an example'.</p>
'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to comment out a large block of code.
<?php
/*
echo 'This is a test'; /* This comment will cause a problem */
*/
?>
add a note
User Contributed Notes
Comments - [15 notes]
fun at nybbles dot com ¶
6 years ago
M Spreij ¶
8 years ago
A nice way to toggle the commenting of blocks of code can be done by mixing the two comment styles:
<?php
//*
if ($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;
}
// */
?>
jballard at natoga dot com ¶
2 years ago
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 ;)
<?php
// Control
echo microtime(), "<br />"; // 0.25163600 1292450508
echo microtime(), "<br />"; // 0.25186000 1292450508
// Test
echo microtime(), "<br />"; // 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(), "<br />"; // 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).
Anonymous ¶
7 years ago
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).
Steve ¶
8 years ago
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
/*
$f->setPattern('/^\d.*/');
*/
?>
Clem at no dot spam ¶
2 months ago
Uncommented:
<?php
/**/
echo "foo";
/**/
?>
Commented:
<?php
/** /
echo "foo";
/**/
?>
hcderaad at wanadoo dot nl ¶
8 years ago
Comments in PHP can be used for several purposes, a very interesting one being that you can generate API documentation directly from them by using PHPDocumentor (http://www.phpdoc.org/).
Therefor one has to use a JavaDoc-like comment syntax (conforms to the DocBook DTD), example:
<?php
/**
* The second * here opens the DocBook commentblock, which could later on<br>
* in your development cycle save you a lot of time by preventing you having to rewrite<br>
* major documentation parts to generate some usable form of documentation.
*/
?>
Some basic html-like formatting is supported with this (ie <br> tags) to create something of a layout.
theblazingangel at aol dot com ¶
5 years ago
it's perhaps not obvious to some, but the following code will cause a parse error! the ?> in //?> is not treated as commented text, this is a result of having to handle code on one line such as <?php echo 'something'; //comment ?>
<?php
if(1==1)
{
//?>
}
?>
i discovered this "anomally" when i commented out a line of code containing a regex which itself contained ?>, with the // style comment.
e.g. //preg_match('/^(?>c|b)at$/', 'cat', $matches);
will cause an error while commented! using /**/ style comments provides a solution. i don't know about # style comments, i don't ever personally use them.
mst_NO_SPAM_TO_ME at mstsoft dot com ¶
7 years ago
This "comment ends on line break or end of PHP Block" thing can be confusing. I discovered this by accident when working with XML Output from PHP...
<?PHP
header("Content-type: text/xml");
/*
echo "<?xml version=\"1.0\"?>";
echo "<page>multi-line comments work as expected.</page>";
*/
//echo "<?xml version=\"1.0\"?>";
//echo "<page>single-line comments end php mode and output your code.</page>";
?>
I would expect the comment to work, but there is no parsing in comments so the String suddenly becomes a PHP end-block tag, which is correct reading this documentation.
cheers,
martin
PS: You even see the behavior in the Syntax highlighting :-)
J Lee ¶
7 years ago
MSpreij (8-May-2005) says /* .. */ overrides //
Anonymous (26-Jan-2006) says // overrides /* .. */
Actually, both are correct. Once a comment is opened, *everything* is ignored until the end of the comment (or the end of the php block) is reached.
Thus, if a comment is opened with:
// then /* and */ are "overridden" until after end-of-line
/* then // is "overridden" until after */
philip-php at dago dot yourweb dot de ¶
2 years ago
It's true, comments do not take up PROCESSING time, but they do take some PARSING time in case you are not using a compile cache of some kind.
samuli dot karevaara at lamk dot fi ¶
7 years ago
If you want to comment out large sections of code (temporarily, usually and hopefully), consider using
<?php
if (0) {
print("This code is 'commented' out");
}
?>
instead of /* comment block */. Otherwise, as noted here, you will have parse errors if the block that you commented out contains */ somewhere, like in regexp or in another comment.
benny at bennyborn dot de ¶
2 years ago
This regex should do the job when trying to parse comments
(\/\*(.*?)\*\/)|(^|\s+)\/\/(.*?)(\n|$)|(^|\s+)#(.*?)(\n|$)
Wolfsbay at ya dot ru ¶
3 years ago
If you are using editor with code highlight, it’s much easier to notice error like /* */ */.
team at researchbib dot com ¶
1 year ago
when the comment string contains '?>', you should be careful.
e.g. output code 1= code 2 is different with code 3
1. with //
<?php
// echo '<?php ?>';
?>
2. with #
<?php
// echo '<?php ?>';
?>
3. with /* */
<?php
/* echo '<?php ?>';*/
?>