Beginner PHP Tutorial - 43 - include_once and require_once Video Lecture | PHP for Absolute Beginners: From Novice to PHP Master - Web Development

hi this is Alex from PHP calamita org
and this is a PHP video tutorial for the
new Boston now we've already looked at
include and require but what about
require once now require once looks like
this it works exactly the same one as in
at one it works exactly the same way
sorry as require and include on their
own you can also use include once as
well now but why would you want to use
this I mean presumably if I was to say
require my header Inc dot PHP file which
I've got up here which just has some
HTML data in and I was to go and refresh
the page you can see that it just says
Alex's page so we've included this we've
required this header in there's not
really any difference in output when we
do require once it's exactly the same
thing it produces exactly the same
result but there's one difference if you
use require once throughout your page it
will check to see if this file has
previously been required and if so won't
require it so let's have a go at now
requiring and just requiring not
requiring one's head adding dot PHP in
here so let's press f5 now you can see
that it's required or included if you
like the file twice now bear in mind
that throughout this whole process we
can use the include once as well as the
include so require once header dot in
dot PHP and require header dot PHP so
now what this is done is its required
heading dot PHP and once but then it's
required it again without using the once
so let's try and swap these around and
see what result we get out ok so you can
see that what's happened is we've
already required or included if you like
the header Inc dot PHP so now what this
what this statement will do if you like
it will check to see if the header Inc
dot PHP has already been included and it
will it will include it if if
if it hasn't been included and if not
then it won't and require once is
similar to doing something like this if
defined and then you choose header dot
php' within this function or this
language construct if defined then
require header Inc dot PHP so what I've
just wrote written here is exactly the
same as the require one so if we refresh
now we can see that we don't have a
record we don't have another version of
it required in here however if I was to
swap them around again so vice versa
that's what I already did a moment
they're going to swap them back around
and I click refresh you see
oh no that two are two unincluded so
this will be now been if not defined
when we refresh you can see that two of
them come up so forget this for now that
was just an example but when we use the
require once we just ensure that the
same file isn't required twice now why
might we want to do this bear in mind
the whole time you can use the include
once that's just different ways to
handle the errors include will include
the file if it doesn't exist and it will
continue with the rest of the page
content require will stop the page so
including require ones why might we want
to require them use them sorry so if
we've got a large sake or fire where we
keeping variables different functions
connecting to our database just things
like that and we then go to require the
file twice we're significantly slower
slowing down the execution of the page
and the reason for this is we're
requiring something twice or including
something twice without using this
underscore once means that it will
actually require it twice so you'll be
processing an include page more than
once so that's the main reason that you
would use it some people have said that
the require and include once language
constructs will actually slow down a
page anyway however nowadays with the
processing time it won't actually make
much difference so you're much better
off using this include
school once or require underscore once
to save the speed of your page for later
on just in case you do happen to include
or require something more than once