1. Putting php code in other files
If you start writing your php scripts they get longer and longer. If you write other php scripts which have the similar layout you get a new php script which gets longer and longer. It would make more sense if you can put this code somewhere else and just say load the code xyz. One way would be to put the code inside a function, but this must be written in the php script and the same function may be written and use in other php scripts, too. So its better to use include. This language construct is given a filenamen and the php script loads this file as php code.
2. Include
If you use the language construct include the following actions take place in background.
-
Leave the php modus (
?>). -
Load and execute the file.
-
Reenter php modus (
<?php).
The execution is the same as the file contents is copy&pasted
at the place where the include statement was.
<p>
HTML Code in a file called <code>file.html</code>.
</p>
<?php
// content of a php file called index.php which is opened by an user
echo 'Before the include';
include 'file.html';
echo 'After the include';
?>
You will get the following html output.
Before the include<p>
HTML Code in a file called <code>file.html</code>.
</p>
After the include
Now you see why include is leaving the php code. This way you can easily output html files. Internally it would looks like this.
<?php
// content of a php file called index.php which is opened by an user
echo 'Before the include';
?><p>
HTML Code in a file called <code>file.html</code>.
</p>
<?php
echo 'After the include';
?>
That means if you want to load php files as php scripts you must still use
<?php and ?> in your files.
<?php
// File: foobar.php
echo "A second line\n";
?>
<?php
// File: index.php, opened by an user
echo "First line\n";
include 'foobar.php';
echo "Third line\n";
?>
Generates the following output.
First line A second line Thrid line
PHP has done something like this.
<?php
// File: index.php, opened by an user
echo "First line\n";
?><?php
// File: foobar.php
echo "A second line\n";
?><?php
echo "Third line\n";
?>
If we delete this ?<>?php lines we see the complete
php code we wants.
<?php
// File: index.php, opened by an user
echo "First line\n";
// File: foobar.php
echo "A second line\n";
echo "Third line\n";
?>
For this reason we also can use variables which are used in another file.
<?php
// File: config.php
$surname = 'John';
$lastname = 'Doe';
?>
<?php
// file: index.php, opened by the user
include 'config.php';
echo 'I am '.$surname.' '.$lastname.', welcome to my homepage';
?>
3. Include with directories
If you include a file inside a directory and this file also includes a file inside this directory php is looking at two positions for this file. The first position is relative to the file which wants to load the file. The second position is relative to the start script which is loaded in the browser. Here is an example how it works.
<?php
// index.php (opened by the user)
include 'inc/config.php';
echo 'My name is "'.$name.'"';
?>
<?php
// config.php (inside of the directory inc/)
include 'functions.php';
include 'variables.php';
echo "Config loaded\n";
?>
<?php
// functions.php (same directory as the file index.php)
function foobar() {
// ...
}
echo "Functions loaded\n";
?>
<?php
// variables.php (inside of the directory inc/)
$name = 'John Doe';
echo "Variables loaded\n";
?>
The directory and files looks like followed.
index.php functions.php inc/config.php inc/variables.php
If you open the index.php file you will get the following output.
Functions loaded Variables loaded Config loaded My name is "John Doe"
It doesn't matter somehow where the files are which to load (in this case
functions.php and inc/variables.php). Internally
the following happends.
-
At
include 'functions.php';the filefunctions.phpis searched first in the directory where theconfig.phpfile is (ininc/). As it isn't found there it searches at the location of the start script. There is is the file and it gets loaded. -
At
include 'variables.php';the file is search first in the directory where theconfig.phpfile is (ininc/). There it finds the variable and loads it.
This can be a problem as there are two locations for searching a file
(and even more with include_path).
You can disable this if the path to the file starts with ./ or ../
(for the current and parent directory). If this is used the path is always relative to
the start script and not relative to an other include anymore.
For developers this whole thing means that you you simply can use include
without care about the paths where are other files are located or the current file
is located. So you write just include 'variables.php'; instead of
statements like include dirname(__FILE__).'/variables.php';.
4. Return value of include
Include files can use return like functions. This way you can use a
include like a function and save the value in a variable.
<?php
// file.php
return "text";
?>
<?php
// index.php
$var = include 'file.php';
echo $var; // echoes 'text'
?>
The include returns the integer value 1 by default.
This is a common error for beginners which try to load a php script with
sth. like echo include 'news.php' and wonders where this stupid
1 at the end is coming from. So this hint: echo include '...';
doesn't make sense in most of the cases.
