Beginner PHP Tutorial - 64 - ob_start Video Lecture | PHP for Absolute Beginners: From Novice to PHP Master - Web Development

hello this is Alex from PHP academy' org
with another video for the new Boston in
the last tutorial we looked at the
header function and how we can use it to
change headers and we use the more
common example of relocating a user to a
specific page now we're faced with this
problem where we have output before our
page or before our PHP code therefore
this header functions returning an error
so let's just have another look at that
we're saying cannot head a kind of
modify header information headers
already sent by this page and we're
saying on line eight so we're calling
this on line eight now there's a simple
way to resolve this and to solve this
problem we use a function called OB
underscore star now this stands for
output buffering start and what this
function does is it turns out put
buffering on now I'll show you how we
write this in our program or our code
rather and then I'll tell you a bit
about the function and why we have to
use it and what it does so I'm going to
create some PHP tags as well up here
before my output and also before the
code that uses the header so this is
going at the very very top of my page
before any output and we use OB
underscore start just cool simply on its
own with no arguments applied you can
also pull this up a bit so it looks a
bit neater so it's all on one line
okay so OB star will not output any and
anything on the page what will it will
but it will be the page output will be
stored in an internal buffer rather than
as headers so if we have some page
content on here let's say my page this
is my page let's just uh let's say
redirect equals false so we don't do a
redirect
and let's run the page so before we have
this cannot modify header information
with a simple change up here ob start
actually yet let's change this to true
so we do redirect with a simple OB start
called at the top when we refresh now
our page is going to redirect so if
you're receiving this error and that
we've had before we use this let's just
get rid of that if you're receiving this
error here then you need to consider
using the OB start now at the end of the
page it's always good practice to use
another function which will clean the
output so we say OB end OB and clean and
what this function does is clears the
output buffer but doesn't actually give
us any contents back so when we refresh
this that's still going to redirect and
if we change redirect to false so we're
not redirecting and we refresh go back
and refresh okay so if we use OB and
flush and we refresh we get the page
contents out so if the redirect is false
we're not redirecting but we're still
displaying this even if this is not
redirecting if you are redirecting the
page if you're redirecting the page
you'll just need a B and clean and what
this does is it won't output anything on
the page there's no need for that so OB
and flush will put well okay so OB start
is storing the output in an internal
buffer an OB and flush is flushing this
buffer but then producing the contents
back onto the page
however the way you think about it if
you was a
logo user out you don't really need to
display anything you just need to
redirect them maybe to a thank you for
logging it or you know see you soon page
or something so as it stands this is
like this then we change this to true
and we successfully redirect the user to
another page this can also be an an
internal file as well you can say page
equals index dot PHP or page equals bi
dot PHP or anything so it doesn't have
to just be a URL
it can be a either your URL or a file
within your web server