November 2002
Intermediate to advanced
640 pages
16h 33m
English
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8.18. Eliminating “headers already sent” Errors
Problem
You are trying to send a
HTTP header or cookie using header( )
or setcookie( ),
but PHP reports a
“headers already
sent” error message.
Solution
This error happens when you send nonheader output before calling
header( ) or setcookie( ).
Rewrite your code so any output happens after sending headers:
// good
setcookie("name", $name);
print "Hello $name!";
// bad
print "Hello $name!";
setcookie("name", $name);
// good
<?php setcookie("name",$name); ?>
<html><title>Hello</title>Discussion
An HTTP message has a header and a body, which are sent to the client
in that order. Once you begin sending the body, you
can’t send any more headers. So, if you call
setcookie( ) after printing some HTML, PHP
can’t send the appropriate Cookie
header.
Also, remove trailing whitespace in any
include files. When you include a file
with blank lines outside <?php ?> tags, the
blank lines are sent to the browser. Use trim( )
to
remove leading and trailing blank lines from files:
$file = '/path/to/file.php';
// backup
copy($file, "$file.bak") or die("Can't copy $file: $php_errormsg);
// read and trim
$contents = trim(join('',file($file)));
// write
$fh = fopen($file, 'w') or die("Can't open $file for writing: $php_errormsg);
if (-1 == fwrite($fh, $contents)) { die("Can't write to $file: $php_errormsg); }
fclose($fh) or die("Can't close $file: $php_errormsg);Instead of processing files on a one-by-one basis, it may be more convenient to do so on a ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.