44 comments

• 

  Adrian Angelov

  8 months ago

  Well, thank got I ran on this post.
  
  I have had this problem, however, no white spaces or whatsoever prior <?php tag. I was really frustrated as the file contained only one line <?php header("Location: /subdir/index.php");?> and this was not working as expected.
  
  The issue turned out to be that the file was a UTF-8 encoded file with BOM signature. This was causing the file header to be transferred prior the content has been processed, and therefore I have had the cannot modify headers error.
  
  Please check your files encoding as well as if it seems to you there is no error in your script.
  reply
• 

  MetalGarurumon

  3 months ago

  Thanks! It works now :)))
  reply
• 

  thejimgaudet

  1 month ago

  U DA MAN... Removing DOM fixed it...
  reply
• 

  mark

  1 month ago

  Uh, yeah, that's nice, but....
  
  what if you need your PHP file to be UTF8 because you need non-ANSI characters in your script defined strings?
  
  My UTF8 .php file works fine on Windows 5.2.5, but barfs on a linux build of same version.
  
  Sigh.
  reply
• 

  Anonymous

  1 month ago

  UTF-8 should work fine on any OS. It's the BOM (Byte Order Mark) that causes the problem, but since UTF-8 always has the same byte order it doesn't need a BOM. See http://unicode.org/faq/utf_bom.html#bom5
  reply
• 

  Anonymous

  1 year ago

  In many occasions this is NOT a bug. Look at the following scenario:
  
  You run the code. It is stuck somewhere. You set display_errors=On (in php.ini or somewhere else) and run again. This time is shows some Notice then it is stuck at the point where there is a call for header function and displays this "Warning: Cannot modify header information - headers already sent by (output ...". You are thinking this is the bug you have to fix and try this and that. You are WRONG. Your bug is somewhere else past the header function.
  
  When you run the code with display_errors=On and when you see the first Notice about something, the browser already got the header to display the Notice and cannot change the header in the header function which follows after the Notice(s).
  
  That means you cannot see any errors past a header function with display_errors=On and there are some notice(s) you wish to ignore.
  
  The solution is resolve all the notices prior to that warning or keep the display_errors=Off and see the error log to find the real problem. Thanks
  reply
• 

  Anonymous

  1 year ago

  Good Day!
  
  i do consider this as a bug. Setting display_error = Off only hides the message error from the user's GUI. And still your header('location: xxx.php') wont work. If you dont have much time tracing your scripts, try this solution:
  
  output_buffering = 4096
  
  good day
  reply
• 

  Anonymous

  1 year ago

  <ul id="quote"><h6>mgingco wrote:</h6>Good Day!
  
  i do consider this as a bug. Setting display_error = Off only hides the message error from the user's GUI. And still your header('location: xxx.php') wont work. If you dont have much time tracing your scripts, try this solution:
  
  output_buffering = 4096
  
  good day</ul>
  
  Get rid of the white space before and after <?php ?> tag, it works.
  reply
• 

  Dan

  4 months ago

  It did work! Colour me amazed! Ta!
  reply
• 

  Anonymous

  10 months ago

  I am going through this very problem now and am having a hell of a time finding it and solving the issue. In fact I have separate scripts that are both having a redirect issue. I cannot find anything in these scripts that would be outputting data to the browser before the header redirect. I have no whitespace before or after <?php ;?> tags.
  
  I am baffled. These are hard to solve sometimes.
  
  Dave
  reply
• 

  qmchenry

  10 months ago

  It can definitely be tough finding the culprit, particularly in a big set of scripts that you didn't write. Since the output has been sent already, it should be present above the error message in the page source that has been sent, so when you see the error, use your browser's View Source to look at what was sent before the error message and you might get something to search for in your source code. If it's something like <head> then you're in luck since you probably only have one of those in a file. If it's a
  then it may be a little tougher, but at least it's something.
  
  One additional tip is to exclude the final ?> tag in a file. This tag isn't necessary and if it isn't present, then there cannot be any whitespace after it.
  
  Good luck!
  reply
• 

  Anonymous

  10 months ago

  Well, the problem is that there is no source to look at because it is PHP, which leads me to believe that no output has been written ... otherwise, I would see something in the source. So, one would think possibly whitespace but I have not found that to be the case either. Very frustrating getting stopped by something like this.
  
  Dave
  reply
• 

  Tim Glenn

  8 months ago

  Great this helped me out a bunch. I would also use these commands to help debug:
  
  ini_set('display_errors', true);
  ini_set('display_startup_errors', true);
  error_reporting (E_ALL);
  reply
• 

  elz

  8 months ago

  i am getting this error even though i dont have header() redirect code.
  
  the lines that prints out the error are on my setcookie() events.
  reply
• 

  elz

  8 months ago

  thought i would add that my problem was easily fixable via the same methods as it is still technically the same issue - setting values after outputting.
  
  just wanted to broaden the horizon on problems that generate this error output
  reply
• 

  Quinn McHenry

  8 months ago

  That's great -- thanks for sharing! I haven't run into this before, but now that you point it out, it makes sense.
  reply
• 

  Andrei

  8 months ago

  Thanks a lot for this post!
  #3 solved my problem! :)
  reply
• 

  Affordable Web Design

  7 months ago

  Good advice thanks for the post
  reply
• 

  P M

  7 months ago

  Very informative article. It was the blank line that was my problem. This article clearly explains subtle issues.
  
  Thanks
  reply
• 

  Packing Machines

  7 months ago

  I had the same problem. the congif-sample file is having two empty lines at the end and they were causing trouble.
  Take care
  Problend
  reply
• 

  carlos

  6 months ago

  sigh , my god my I knew about the problems with the header since a long time ago, Ive been using PHP for years but today I just couldtn find what was wrong with mine, my header was on top of my page, no echos, everything seemed so clean...then I googled this and there you go, a single space was messin it up, this is exactly how my code was
  <?php
  ......
  ?>
  all i had to do was
  <?php
  ......
  ?>
  
  can you not the difference? i couldnt either :(
  reply
• 

  Jon

  6 months ago

  This had me pulling my hair out for hours today.
  
  I had all my php code before the HEAD without any whitespace. (you can't imagine how many times I pressed the delete key trying to get rid of white space that wasn't there :)
  
  Anway, the culprit was that Dreamweaver saved the .php file as as a UTF-8 format file (I had renamed it from a UTF .html file .. so it's really my fault).
  
  When a .php file is saved as UTF it inserts a
  line break before everything, but it will be invisible in Dreamweaver.
  
  What you have to do is open the .php file in notepad, and 'Save as' ANSI.
  
  And now, you're good to go!
  
  reply
• 

  Full time link builder hire

  6 months ago

  thanks jon for sharing , i have faced the same problem with Dreamweaver, your input helped me to over come it. Many many hours spent on this before I got this article on google.
  reply
• 

  Chris

  5 months ago

  Thanks!
  reply
• 

  Fr

  5 months ago

  Strange issue, I've removed header completely from html, actually, completely <html> tags, and only with
  <?php
  ......
  header("location:../first.php");
  ?>
  then it is working properly.
  I've got a line with echo before the header, and got the same warning - Cannot modify header information - headers already sent.
  This is happening on a linux environment, on windows (+Apache+mysql) I've got no such a messages, well, I didn't compared those two php.ini properly.
  Anyway, thanks for help.
  reply
• 

  Klaus

  5 months ago

  Thanks, helped me a lot.
  Amazing what some additional unnoticed whitespace can cause havoc
  sometimes.
  reply
• 

  Sachin

  4 months ago

  hi
  please help me.. please please please.
  please take a look at the following script:
  it is giving the following errors
  ---------------------------------------------------------------------------------------
  Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /home/compkcom/public_html/cmpanel/check_login.php on line 11
  
  Warning: Cannot modify header information - headers already sent by (output started at /home/compkcom/public_html/cmpanel/check_login.php:11) in /home/compkcom/public_html/cmpanel/check_login.php on line 19
  ---------------------------------------------------------------------------------------
  here goes the php script
  ----------------------------------------------------------------------------------------------------
  <?php session_start();
  if((isset($_POST['username'])&&$_POST['username']!="")&&(isset($_POST['password'])&&$_POST['password']!="")){
  $error='';
  $conn = mysql_connect('localhost','compkcom_care','ptk')or die('Could not connect to MySQL database. ' . mysql_error());
  mysql_select_db(SQL_DB,$conn);
  $query = "SELECT COUNT(username) AS record FROM admin WHERE username ='" . $_POST['username']."' AND password = '".$_POST['password']."'";
  $result = mysql_query($query);
  $row = mysql_fetch_array($result);
  if($row['record']==1){
  $_SESSION['user_logged'] = $_POST['username'];
  $_SESSION['user_password'] = $_POST['password'];
  header("location:welcome.php");
  }
  else{
  $error .="Please+Enter+Correct+Username+and+password%21%0D%0A";
  header("location:index.php?&error=".$error);
  }
  }
  else{
  $error .="Please+Enter+the+Username+and+password+First%21%0D%0A";
  header("location:index.php?&error=".$error);
  }
  ?>:
  ----------------------------------------------------------------------------------------------------
  this script is running fine on my local windows server but giving the above mentioned errors on my linux hosted server..
  Please help me...
  Thanks..
  reply
• 

  Quinn McHenry

  4 months ago

  Your database query may not be returning a valid result. It's good practice to make sure the result returned from your mysql_query command is valid.. something like:
  
  if (!$result) {
  die('Invalid query: ' . mysql_error());
  }
  
  Dumping the error message may help in this case, too.
  
  Good luck!
  reply
• 

  dave

  4 months ago

  wwwwwwwwwwwwwoooooow thanks sir problem solved,, stupid white space
  reply
• 

  dominic

  4 months ago

  This helped me to some my problem. Where i was trying to generate a xml file using php.
  
  Thanks
  reply
• 

  Fr

  4 months ago

  Actually, there are some solution, problem is well documented on link:
  http://php.net/manual/en/function.header.php
  
  It is related to earlier versions of PHP, or to setup in php.ini
  I've put on the very first line:
  <?php
  ob_start();
  session_start();
  ?>
  Now, everything works fine, i-e you can have more than one header in your code.
  reply
• 

  RORO

  3 months ago

  This did it! THANKS SO MUCH!! Nothing else worked and I tried it all!
  reply
• 

  manuel

  2 months ago

  how can modify display_error in php script ?
  reply
• 

  Lito

  2 months ago

  Warning: Cannot modify header information - headers already sent by (output started at /home/misaghi/public_html/config.php:47) in /home/misaghi/public_html/login_process.php on line 79
  reply
• 

  IMQ

  2 months ago

  this error will be thrown if u have any white spaces or any print or echo above header call.
  There should be no print , no echo and no spaces before or after header statement.
  reply
• 

  bapo333

  1 month ago

  thnks.........
  i have been working on the same for the past 5 days........... the error i had was a space before PHP tag..
  reply
• 

  Andy

  1 month ago

  Legendary stuff... this article just saved my sanity. A white space after the close php tag in an 'include' file caused my hours of frustration.
  
  Thank you!
  reply
• 

  neoniflor

  4 weeks ago

  That was fun..... whitespace really where a problem... thanks
  reply
• 

  Mithus

  3 weeks ago

  That really great....thanx.....sooo mch....
  reply
• 

  Jamie

  3 weeks ago

  Ugh. Of course!! My problem was, as you said, hiding in plain site. I was echoing a file upload verification right before calling header(), and I didn't even notice it.
  
  Thanks for the easy instructions!
  reply
• 

  Leandro

  2 weeks ago

  I had an include with two blank lines after the ?> in that include... I deleted those blank lines and It works perfectly!
  
  Thanks!
  reply
• 

  dinesh

  2 weeks ago

  Make sure there is no white space outside of the php start and end tags
  
  This is really a culprit.
  Thanks for help.
  reply
• 

  Emmanuel Afonrinwo

  1 week ago

  Thanks a lot, after reading and carefully looking through the codes paying attention to your advice theproblem was resolved.
  reply
• 

  Charlies

  2 days ago

  I am not getting this error on my local PC, but when I upload the scripts to the hosting provide I get this error. How can I set my local machine to display the same error
  
  Cheers
  reply