<p>This is going to be ignored by PHP and displayed by the browser.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored by PHP and displayed by the browser.</p>
<?php
$a = 1; /* global scope */
function test()
{
echo $a; /* reference to local scope variable */
}
test();
?>
Regarding earlier note by @purkrt :
> I would like to stress out that the opening tag is "<?php[whitespace]", not just "<?php"
This is absolutely correct, but the wording may confuse some developers less familiar with the extent of the term "[whitespace]".
Whitespace, in this context, would be any character that generated vertical or horizontal space, including tabs ( \t ), newlines ( \n ), and carriage returns ( \r ), as well as a space character ( \s ). So reusing purkrt's example:
<?php/*blah*/ echo "a"?>
would not work, as mentioned, but :
<?php /*php followed by space*/ echo "a"?>
will work, as well as :
<?php
/*php followed by end-of-line*/ echo "a"?>
and :
<?php /*php followed by tab*/ echo "a"?>
I just wanted to clarify this to prevent anyone from misreading purkrt's note to mean that a the opening tag --even when being on its own line--required a space ( \s ) character. The following would work but is not at all necessary or how the earlier comment should be interpreted :
<?php
/*php followed by a space and end-of-line*/ echo "a"?>
The end-of-line character is whitespace, so it is all that you would need.
<?php
$foo = "1"; // $foo is string (ASCII 49)
$foo *= 2; // $foo is now an integer (2)
$foo = $foo * 1.3; // $foo is now a float (2.6)
$foo = 5 * "10 Little Piggies"; // $foo is integer (50)
$foo = 5 * "10 Small Pigs"; // $foo is integer (50)
?>
"<script language="php"> </script>, are always available." since PHP 7.0.0 is no longer true. These are removed along the ASP "<%, %>, <%=" tags.
<?php
class SimpleClass
{
// property declaration
public $var = 'a default value';
// method declaration
public function displayVar() {
echo $this->var;
}
}
?>
One aspect of PHP that you need to be careful of, is that ?> will drop you out of PHP code and into HTML even if it appears inside a // comment. (This does not apply to /* */ comments.) This can lead to unexpected results. For example, take this line:
<?php
$file_contents = '<?php die(); ?>' . "\n";
?>
If you try to remove it by turning it into a comment, you get this:
<?php
// $file_contents = '<?php die(); ?>' . "\n";
?>
Which results in ' . "\n"; (and whatever is in the lines following it) to be output to your HTML page.
The cure is to either comment it out using /* */ tags, or re-write the line as:
<?php
$file_contents = '<' . '?php die(); ?' . '>' . "\n";
?>
it's perhaps not obvious to some, but the following code will cause a parse error! the ?> in //?> is not treated as commented text, this is a result of having to handle code on one line such as <?php echo 'something'; //comment ?>
<?php
if(1==1)
{
//?>
}
?>
i discovered this "anomally" when i commented out a line of code containing a regex which itself contained ?>, with the // style comment.
e.g. //preg_match('/^(?>c|b)at$/', '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.
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.
<?php
$foo = 'Bob'; // Assign the value 'Bob' to $foo
$bar = &$foo; // Reference $foo via $bar.
$bar = "My name is $bar"; // Alter $bar...
echo $bar;
echo $foo; // $foo is altered too.
?>