PHP 5.4: prevent headers from being set after output

Question

I am used to headers not being able to be sent after output has started. In fact, I count on it.

In the application I'm working on, after every succesful updating or inserting query, the page is reloaded with a header('Location: ...') call. That's because I don't want the page with the POST data to be refresh-able.

But while developing, one of these queries might just have a bug in them - and then I'm printing out some debug information (with echo). This would then prevent the page from being reloaded - but ever since I upgraded to php 5.4, it simply reloads anyway. I can only read the debug information if I exit; after printing the debug information - which I don't like, because some more debug information might follow later in the script.

If I check headers_sent() in one of those echo calls, it says headers have not been sent yet. So it looks like it's being buffered without me (knowingly) having turned that on.

It might of course be a php.ini setting rather than the mere fact I'm now using version 5.4, but I can't find it.

Someone have an idea?

What is the value of output_buffering in your php.ini file? — jeroen
– jeroen, Commented Sep 14, 2012 at 14:41
Thank you jeroen - it's silly, but I had looked over this value. output_buffering is indeed set (to 4096) which causes my debug information to be automatically kept in buffer, allowing the header to be set. It must have been off on my previous php installation. — Sygmoral
– Sygmoral, Commented Sep 14, 2012 at 16:06

Community · Accepted Answer · 2023-11-14 22:27:54Z

1

Use output buffering to solve this. Basically all you need to do is to call ob_start(); as soon as you can. Then, instead of sending stuff out instantly, PHP would buffer the output. So it does not really matter what you set first, body or headers. They will be set in buffer, so manipulation is not a problem unless buffer is sent. If you do not flush buffer explicitly it will be sent by PHP when your script ends. See Output Buffering Control chapter in PHP manual.

edited Nov 14, 2023 at 22:27

CommunityBot

11 silver badge

answered Sep 14, 2012 at 14:27

Marcin Orlowski

75.7k11 gold badges128 silver badges152 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Sygmoral Over a year ago

I understand your suggestion, but I don't think that's what I want: I do NOT want buffering, but I seem to be getting it anyway. I do in fact want the header() call to fail due to the output having been started, so that I can see the debug information.

Sygmoral Over a year ago

It was indeed an output buffering issue though - thanks to jeroen's comment on my original question, I was able to find that php was automatically buffering output due to output_buffering being set in php.ini.

Sygmoral · Accepted Answer · 2012-09-14 16:11:13Z

1

jeroen answered my question (in a comment on my original question) by pointing me to the output_buffering setting in php.ini. Thank you!

answered Sep 14, 2012 at 16:11

Sygmoral

7,2012 gold badges27 silver badges33 bronze badges

Collectives™ on Stack Overflow

PHP 5.4: prevent headers from being set after output

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related