Quando il PHP inizia a esaminare un file, cerca i tag di apertura e di chiusura, che sono <?php e ?>, i quali indicano dove iniziare e terminare l'interpretazione del codice. Questa tecnica permette al PHP di essere incorporato in tutte le tipologie di documenti, poiché ogni cosa esterna ai tag di apertura e di chiusura viene ignorata dal parser PHP.

PHP permette anche dei tag abbreviati <? e ?> (che sono sconsigliati in quanto sono disponibili solo se abilitati con la direttiva short_open_tag nel file di configurazione php.ini, oppure se PHP è stato configuration con l'opzione --enable-short-tags .

Se un file contiene solo codice PHP, è cosniglato di omettere il tag di chiusura PHP alla fine del file. Questo evita che vengano aggiunti spazi o ritorni a capo dopo il tag di chiusura, che può creare effetti indesiderati poiché PHP comincerà a processare l'output quando in realtà non c'è intenzione da parte dello sviluppatore di inviare dell'output in quella parte dello script.

echo "Hello world";

// ... altro codice

echo "Last statement";

// lo script finisce qui senza tag di chiusura

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User Contributed Notes 6 notes

crazytonyi at gmail dot com
2 years ago
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 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 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.
Mark Clements (kennel17.co.uk)
3 months ago
Closing PHP tags are recognised within single-line comments:

// Code will end here ?> This is output as literal text.

# Same with this method of commenting ?> This is output as literal text.

However they do not have an effect in C-style comments:

/* Code will not end here ?> as closing tags are ignored inside C-style comments. */
dave at juuce dot com
6 months ago
// ///////
// comments

Found that single line comments cause issues and received "notice: use of undefined constant php - assumed 'php'" for line 1 of file.

// //////
// comments

Add a space character after <?php on the first line corrects the problem.
raoni at gmail dot com
2 months ago
If short_open_tag = Off

<?php/*php not followed by space*/ echo "a"?>
This will not be parsed by php

If short_open_tag = On

<?php/*php not followed by space*/ echo "a"?>
This will be parsed by php, but it throw "Parse error: Syntax error ..." because because 'php' will be assumed as a constant

<?/*? not followed by space*/ echo "a"?>
This will be parsed by php,  and work fine.

(Tested in php 7.1)
purkrt at gmail dot com
3 years ago
I would like to stress out that the opening tag is "<?php[whitespace]", not just "<?php". While this might seem blatantly obvious, I thought for some time that

<?php/*blah*/ echo "a"?>

would work, and it does not; the comment does not work as whitespace. I've run into this while converting some older code with short open tag.
alexander dot podgorny at somewhere dot com
3 years ago
One reason to use long tags over short is to avoid confusion with <?xml ?> notation.
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