PHP: Комментарии

PHP поддерживает комментарии в стиле языков программирования C, C++ и в стиле командной оболочки Unix-систем, которая унаследовала стиль комментариев из языка Perl. Например:

<?php
    echo "Это тест"; // Это однострочный комментарий в стиле языка C++
    /* Это многострочный комментарий
       ещё одна строка комментария */
    echo "Это ещё один тест";
    echo "Последний тест"; # Это комментарий в стиле Unix-оболочки
?>

Однострочные комментарии распространяются только до конца строки PHP-кода или на текущий блок PHP-кода в HTML-строке, в зависимости от того, что идёт первым. Поэтому HTML-код после начала однострочного комментария // ... ?> или # ... ?> выводится: тег ?> прерывает режим разбора PHP-кода и возвращает режим HTML-разметки, и символы // или # не влияют на это.

<h1>Это <?php # echo "простой";?> пример</h1>
<p>Заголовок вверху выведет 'Это  пример'.</p>

Комментарии в стиле языка C заканчиваются, когда обнаруживается первая последовательность */. Программисты следят за тем, чтобы комментарии в стиле языка C не оказались вложенными. Ошибку с вложенными C-комментариями часто допускают, когда комментируют большой блок кода.

<?php
 /*
    echo "Это тест"; /* Этот комментарий вызовет ошибку */
 */
?>

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Инструкция • Исправление • Сообщение об ошибке

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Примечания пользователей 11 notes

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450

J. Prettyman ¶

10 years ago

Notes can come in all sorts of shapes and sizes. They vary, and their uses are completely up to the person writing the code. However, I try to keep things consistent in my code that way it's easy for the next person to read. So something like this might help...

<?php

//======================================================================
// CATEGORY LARGE FONT
//======================================================================

//-----------------------------------------------------
// Sub-Category Smaller Font
//-----------------------------------------------------

/* Title Here Notice the First Letters are Capitalized */

# Option 1
# Option 2
# Option 3

/*
 * This is a detailed explanation
 * of something that should require
 * several paragraphs of information.
 */
 
// This is a single line quote.
?>

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318

M Spreij ¶

19 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;
}
// */
?>

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aetonsi ¶

2 years ago

As of php 8, single line comments starting exactly with "#[" have a special meaning: they are treated as "attributes", and they must respect the expected syntax. See: https://www.php.net/manual/en/language.attributes.php

So the following code throws an error in php 8+, while it is perfectly valid in php <8:
<?php
#[~~my super cool comment~~~]
?>

To be safe, just always use "//" comments instead of "#". Maybe in the future there will be other special meanings for the "#" comments, who knows.

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143

magnesium dot oxide dot play+php at gmail dot com ¶

11 years ago

It is worth mentioning that, HTML comments have no meaning in PHP parser. So,

<!-- comment
<?php echo some_function(); ?>
-->

WILL execute some_function() and echo result inside HTML comment.

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hcderaad at wanadoo dot nl ¶

19 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.

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J Lee ¶

18 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 */

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Steve ¶

20 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.*/');

*/

?>

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theblazingangel at aol dot com ¶

17 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.

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jballard at natoga dot com ¶

14 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).

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Wolfsbay at ya dot ru ¶

14 years ago

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

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fun at nybbles dot com ¶

18 years ago

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");
         }
?>

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