php包含和关闭标记

Question

Saw a thread about omitting the closing ?> in PHP scripts and got me wondering.

Take this code:

foo.php

<?php
echo 'This is foo.php';
include('bar.php');

bar.php

<?php   
echo 'This is bar.php';

If you create these two scripts and run them, php outputs:

This is foo.php
This is bar.php

(new line added for artistic license before anyone points that out)

So, how come: baz.php

<?php
echo 'This is foo.php';

<?php
echo 'This is bar.php';

results in a predictable syntax error unexpected '<' , when "include" does just that - or rather, my understanding of include is that PHP just dumps the file at that point as if it had always been there.

Does PHP check for opening tags and ignore future ones if the file is included? Why not do this when there are two sets of tags in one script?

Thanks for any clarification. Not exactly an important issue but would be nice to understand PHP a little more.

Answer 1

If you include a file, PHP internally switches from parsing to literal mode (ie what it normally does on a closing tag. That's why this works:

<?php
include 'foo.php';
?>

//foo.php
<?php
echo 'yo';
?>

Even though when inlined it would become

<?php
<?php
echo 'yo';
?>
?>

Because interally it's transformed into something like this (for illustrative purposes, in reality it probably doesn't actually merge the contents of the files, it just jumps between them)

<?php
?>
<?php
echo 'yo';
?>
<?php
?>

You can omit the closing ?> because at the end of the include file, PHP switches back to parsing the including file, regardles of what mode it's currently in.

Answer 2

Personal speculation:

When you write include('bar.php'); , the parser reads the content fo bar.php and inserts it into foo.php , when reading it probably strips the starting <?php since it recognise all the content of bar.php is PHP code, hence the result does not yelds to an error.

Answer 3

It might help to think of it as PHP not actually including the other page inside the first one, as in PHP doesn't internally create a single file with all included pages inside and then parse that.

What it does is that it parses the first file, finds include and then stops parsing the first file and starts parsing the included file. When the included file is done it resumes parsing the original file where it left off. (This is quite a bit simplified though.)

Answer 4

I somewhere read about omitting both opening and closing php tags.

The problem when I do this is that my editor doesn't format the files as php files but as regular text files.

up till now I never had a problem with any include file that has the tags. I don't know if it is depreciated behavior to use the tags or not.