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About Comments - Images: Japanese
Hey there, everyone!
Next up, let's look at 'comments' and 'commenting out'. HTML has comments too, and in fact pretty much every programming language has a comment feature. Adding a comment or turning something into a comment is often called "commenting out." So 'comment' is the noun and 'comment out' is the verb.
Let's take a fresh look at what a 'comment' actually is. The syntax varies by language, but the one thing they all have in common is that the code inside a 'comment' is never executed.
So let's quickly refresh our memory on HTML comments. An HTML comment looks like this:
<!-- This is a comment. -->
Written this way, the content is treated as a 'comment' and won't be rendered by the browser.
However, there's an important caveat with HTML comments worth remembering. An HTML comment is just not rendered — it still exists as plain text in the file. That means if a visitor clicks "View Page Source" in their browser, they can read your comment right there.
<!-- HTML comments are visible to anyone viewing the source, so writing unreleased info like this is asking for trouble. --> <!-- Hey engineers: please publish the following item on Feb 7. --> <!-- <a href="/new.html">Dragon of Fantasy 12 releases on March 7!</a> -->
With a dynamic language like PHP, however, comments are never executed and therefore never output as text — so you can freely write unreleased info or anything else you'd like without it leaking to visitors.
<?php // With PHP comments, nothing here is ever output as text. Feel free to write unreleased info, vent about your boss, or scribble whatever's on your mind. // Hey engineers: please publish the following item on Feb 7. // <a href="/new.html">Dragon of Fantasy 12 releases on March 7!</a>
So when building websites with PHP, it's generally a good idea to use 'PHP comments' rather than 'HTML comments' wherever possible.
Now let's go through the PHP comment syntax. PHP has two types of comments: 'single-line comments' and 'block comments'.
First, single-line comments. Adding '//' or '#' makes everything from that point to the end of the line a comment. As for which one is more common — it's probably about half and half, so feel free to use whichever you prefer.
<?php // This is a 'comment'. # This is also a 'comment'.
One thing to keep in mind with PHP single-line comments: a single-line comment ends at either a 'newline' or a 'PHP closing tag'. Pay particular attention to the behavior where a comment ends at the PHP closing tag — it's a PHP-specific gotcha that comes from its HTML-embedding design.
<?php // This is a 'comment'. // This part is a 'comment'. ?>But this is outside the PHP block, so it's NOT a comment. It gets output normally.
Next, block comments. These are for multi-line comments. Just wrap the content between '/*' and '*/' and that entire section becomes a comment.
<?php /* This is a comment. You can span multiple lines. */ ?>
This applies to other languages too, but be careful not to nest /* and */ inside each other. In the example below, the first */ encountered ends the comment, leaving a stray */ which causes an error.
<?php /* /* Nesting like this will cause unexpected behavior. */ */ ?>
Also, unlike single-line comments, a block comment does NOT end at a PHP closing tag.
<?php /* A PHP closing tag does not end a block comment. ?>see */ echo 'Hello world';
Think of it as the '?>' being treated as part of the comment. Easy to get tripped up on, so keep it in mind.
And that covers PHP 'comments'. In the next article, we'll take a look at how PHP handles 'statements', whitespace, newlines, and tab characters. See you there!
This article was written by Sakurama.
Author's beloved small mammal |
桜舞 春人 Sakurama HarutoA Tokyo-based programmer who has been creating various content since the ISDN era, with a bit of concern about his hair. A true long sleeper who generally feels unwell without at least 10 hours of sleep. His dream is to live a life where he can sleep as much as he wants. Loves games, sports, and music. Please share some hair with him. |
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