What s the use of ob start in php

Question

Is ob start   used for output buffering so that the headers are buffered and not sent to the browser  Am I making sense here  If not then why should we use ob start

User · Answer

No  you are wrong  but the direction fits     The Output-Buffering buffers the output of a script  Thats  in short  everthing after echo or print  The thing with the headers is  that they only can get sent  if they are not already sent  But HTTP says  that headers are the very first of the transmission  So if you output something for the first time  in a request  the headers are sent and you can not set any other headers

User · Answer

Following things are not mentioned in the existing answers   Buffer size configuration HTTP Header and Nesting    Buffer size configuration for ob start    ob start null  4096      Once the buffer size exceeds 4096 bytes  PHP automatically executes flush  ie  the buffer is emptied and sent out    The above code improve server performance as PHP will send bigger chunks of data  for example  4KB  wihout ob start call  php will send each echo to the browser      If you start buffering without the chunk size  ie  a simple ob start     then the page will be sent once at the end of the script   Output buffering does not affect the HTTP headers  they are processed in different way  However  due to buffering you can send the headers even after the output was sent  because it is still in the buffer   ob start        turns on output buffering  foo- gt bar        all output goes only to buffer ob clean        delete the contents of the buffer  but remains buffering active  foo- gt render       output goes to buffer ob flush       send buffer output  none   ob get contents        buffer content is now an empty string ob end clean        turn off output buffering   Nicely explained here   https   phpfashion com everything-about-output-buffering-in-php

User · Answer

You have it backwards  ob start does not buffer the headers  it buffers the content   Using ob start allows you to keep the content in a server-side buffer until you are ready to display it   This is commonly used to so that pages can send headers  after  they ve  sent  some content already  ie  deciding to redirect half way through rendering a page

User · Answer

this is to further clarify JD Isaaks answer       The problem  you run into often is that you are using php to output html from many different php sources  and those sources are often  for whatever reason  outputting via different ways    Sometimes you have literal html content that you want to directly output to the browser  other times the output is being dynamically created  server-side     The dynamic content is always    going to be a string  Now you have to combine this stringified dynamic html with any literal  direct-to-display html     into one meaningful html node structure   This usually forces the developer to wrap all that direct-to-display content into a string  as JD Isaak was discussing  so that it can be properly delivered inserted in conjunction with the dynamic html     even though you don t really want it wrapped    But by using ob    methods you can avoid that string-wrapping mess  The literal content is  instead  output to the buffer  Then in one easy step the entire contents of the buffer  all your literal html   is concatenated into your dynamic-html string     My example shows literal html being output to the buffer  which is then added to a html-string     look also at JD Isaaks example to see string-wrapping-of-html     lt  php    parent php    ---------------------------------  lvs html           lvs html      lt div gt html lt  div gt      lvs html    gf component assembler  without ob       lvs html      lt div gt more html lt  div gt       lvs html     ---- lt br  gt       lvs html      lt div gt html lt  div gt      lvs html    gf component assembler  with ob       lvs html      lt div gt more html lt  div gt      echo  lvs html             02 - component contents       html       01 - component header       03 - component footer       more html       ----       html       01 - component header       02 - component contents       03 - component footer       more html     --------------------------------- function gf component assembler  without ob               lvs html      lt div gt 01 - component header lt  div gt         lt table  gt  lt tr gt         include   component contents php           lvs html      lt div gt 03 - component footer lt  div gt         lt  tr gt  lt  table gt          return  lvs html            --------------------------------- function gf component assembler  with ob               lvs html      lt div gt 01 - component header lt  div gt         lt table  gt  lt tr gt              ob start            include   component contents php           lvs html    ob get clean          lvs html      lt div gt 03 - component footer lt  div gt         lt  tr gt  lt  table gt          return  lvs html            ---------------------------------   gt       lt  -- component contents php -- gt     lt div gt      02 - component contents    lt  div gt

User · Answer

Think of ob start   as saying  Start remembering everything that would normally be outputted  but don t quite do anything with it yet    For example   ob start    echo  Hello there       would normally get printed to the screen output to browser  output   ob get contents    ob end clean      There are two other functions you typically pair it with  ob get contents    which basically gives you whatever has been  saved  to the buffer since it was turned on with ob start    and then ob end clean   or ob flush    which either stops saving things and discards whatever was saved  or stops saving and outputs it all at once  respectively

User · Answer

This function isn t just for headers  You can do a lot of interesting stuff with this  Example  You could split your page into sections and use it like this    someTemplate- gt selectSection  header    echo  This is the header      someTemplate- gt selectSection  content    echo  This is some content      You can capture the output that is generated here and add it at two totally different places in your layout

User · Answer

I use this so I can break out of PHP with a lot of HTML but not render it  It saves me from storing it as a string which disables IDE color-coding    lt  php ob start      gt   lt div gt       lt span gt text lt  span gt       lt a href     gt link lt  a gt   lt  div gt   lt  php  content   ob get clean      gt    Instead of    lt  php  content     lt div gt       lt span gt text lt  span gt       lt a href     gt link lt  a gt   lt  div gt      gt

User · Answer

I prefer   ob start    echo  Hello there      output   ob get clean      Get current buffer contents and delete current output buffer

User · Answer

The accepted answer here describes what ob start   does - not why it is used  which was the question asked    As stated elsewhere ob start   creates a buffer which output is written to    But nobody has mentioned that it is possible to stack multiple buffers within PHP  See ob get level     As to the why       Sending HTML to the browser in larger chunks gives a performance benefit from a reduced network overhead  Passing the data out of PHP in larger chunks gives a performance and capacity benefit by reducing the number of context switches required Passing larger chunks of data to mod gzip mod deflate gives a performance benefit in that the compression can be more efficient  buffering the output means that you can still manipulate the HTTP headers later in the code explicitly flushing the buffer after outputting the  head       head  can allow the browser to begin marshaling other resources for the page before HTML stream completes  Capturing the output in a buffer means that it can redirected to other functions such as email  or copied to a file as a cached representation of the content

[php] What's the use of ob_start() in php?

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