What is the difference between include and require?

[noRush]

What is the difference? When should I use include, require or require_once? Thank you!

[merk]

include will include the file, and should it fail, keep running the script.

require will include the file, and should it fail, the script will stop.

include_once and require_once are even more handy if you write scripts that run and include eachother, because including() a file more than once will generate errors, but include_once() will only inlcude the file once, regardless of how many times it is called.

[noRush]

How does it know if it is the same file? By the file name or what is actually in the file?

[Chroder]

Also, require will include the file regardless of control structures etc.


$value = true;

if($value == true)
{
echo "alright";
}

else
{
require("error.php");
}

// error.php will be included, even when $value is true

[merk]

How does it know if it is the same file? By the file name or what is actually in the file?
PHP will keep an internal list of files included. Im not sure exactly how it does it, you could check out the PHP source for the function if you need to :)

There might be more explination in the PHP manual.

[Faruk]

I'm not 100% sure of this at all, but I think PHP just looks at the filename you specify, verifies its location and date, requires (or includes) it, and when a call to the same file is made (it knows which files with what datestamps are included) it checks to see if the date has changed, and if so require it again and if not, doesn't do anything..

That would at least be the logical (and very simple) approach....

[i am coo man]

Also, require will include the file regardless of control structures etc.


$value = true;

if($value == true)
{
echo "alright";
}

else
{
require("error.php");
}

// error.php will be included, even when $value is true
Not true, require works the same as include and is executed like any other code

[merk]

I'm not 100% sure of this at all, but I think PHP just looks at the filename you specify, verifies its location and date, requires (or includes) it, and when a call to the same file is made (it knows which files with what datestamps are included) it checks to see if the date has changed, and if so require it again and if not, doesn't do anything..

That would at least be the logical (and very simple) approach....
From memory (i read this in the manual a while ago), php only stores a list of files, it doesnt use dates

[Scott MacVicar]

it gets the full path
/path/to/filename.php

creates a hash of the path.

When you do an include_once / require_once it checks the hash against its internal hash table and either ignores or includes again.

[Chroder]

Not true, require works the same as include and is executed like any other code
Ah yeah, my bad. Prior to v.4.0.2 ;)

[noRush]

So for v.4.0.2 or higher, it only includes when it need to, but any version lower than v.4.0.2, it always includes it no matter what?
Thanks for the support!:)