Can I use hash sign (#) for commenting in PHP?

问题:

I have never, ever, seen a PHP file using hashes (#) for commenting. But today I realized that I actually can! I'm assuming there's a reason why everybody uses // instead though, so here I am.

Is there any reason, aside from personal preference, to use // rather than # for comments?

回答1:

The answer to the question Is there any difference between using "#" and "//" for single-line comments in PHP? is no.

There is no difference. By looking at the parsing part of PHP source code, both "#" and "//" are handled by the same code and therefore have the exact same behavior.

回答2:

PHP's documentation describes the different possibilities of comments. See http://www.php.net/manual/en/language.basic-syntax.comments.php

But it does not say anything about differences between "//" and "#". So there should not be a technical difference. PHP uses C syntax, so I think that is the reason why most of the programmers are using the C-style comments '//'.

回答3:

<?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
?>

RTM

回答4:

Is there any reason, aside from personal preference, to use // rather than # for comments?

I think it is just a personal preference only. There is no difference between // and #. I personally use # for one-line comment, // for commenting out code and /** */ for block comment.

<?php
    # This is a one-line comment
    echo 'This is a test';

    // echo 'This is yet another test'; // commenting code

    /** 
     * This is a block comment
     * with multi-lines 
     */
    echo 'One final test';
?>

回答5:

One might think that the # form of commenting is primarily intended to make a shell script using the familiar "shebang" (#!) notation. In the following script, PHP should ignore the first line because it is also a comment. Example:

#!/usr/bin/php
<?php

echo "Hello PHP\n";

If you store it in an executable file you can then run it from a terminal like this

./hello

The output is

Hello PHP

However, this reasoning is incorrect, as the following counterexample shows:

#!/usr/bin/php
#A
<?php

#B
echo "Hello PHP\n";

The first line (the shebang line) is specially ignored by the interpreter. The comment line before the PHP tag is echoed to standard output because it is not inside a PHP tag. The comment after the opening PHP tag is interpreted as PHP code but it is ignored because it is a comment.

The output of the revised version is

#A
Hello PHP

回答6:

If you establish some rule sets in your team / project... the 2 types of comments can be used to outline the purpose of the commented code.

For example I like to use # to mute / disable config settings, sub functions and in general a piece of code that is useful or important, but is just currently disabled.

回答7:

There's no official PSR for that.

However, in all PSR example code, they use // for inline comments.

There's an PSR-2 extension proposal that aims to standardize it, but it's not official: https://github.com/php-fig-rectified/fig-rectified-standards/blob/master/PSR-2-R-coding-style-guide-additions.md#commenting-code

// is more commonly used in the PHP culture, but it's fine to use # too. I personally like it, for being shorter and saving bytes. It's personal taste and biased, there's no right answer for it, until, of course, it becomes a standard, which is something we should try to follow as much as possible.

回答8:

Yes, however there are cross platform differences.

I use # all the time for commenting in PHP, but I have noticed an adoption difference.

On windows keyboard the # key is easy to use. On mac keyboard # key mostly isn't present.

So for mac users, [Alt] + [3] or [⌥] + [3] is more difficult to type than //, so // has become a cross platform way of displaying code with comments.

This is my observation.

回答9:

Comments with "#" are deprecated with PHP 5.3. So always use // or /.../