Cannot modify header information [duplicate] - php

Question

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Headers already sent by PHP
My problem is that I have a class with a function inside of it, and I get;
Warning: Cannot modify header information - headers already sent by (output started at /home/user/public_html/inc/class.php:105) in /home/user/public_html/inc/facebook/login.php on line 21
When the page I'm using it on redirects a user with the header(); tag. The class is;
class mysql {
private $user;
private $pass;
private $db;
public function __construct($user1, $pass1, $db1) {
$this->user = $user1;
$this->pass = $pass1;
$this->db = $db1;
$this->connect();
}
public function connect() {
$this->connection = mysql_connect('localhost', $this->user, $this->pass);
$select = mysql_select_db($this->db, $this->connection);
}
public function query($x) {
return mysql_query($x);
}
public function fetch($x) {
return mysql_fetch_array($x);
}
public function num($x) {
return mysql_num_rows($x);
}
}
Line 105 is the;
return mysql_fetch_array($x);
And the file trying to do the header redirect just includes this file at the top of the page and does the header lower down.
Thanks in advance.

Answer 1

What is triggering this error?
This error is triggered when some code has already output to the "screen" before you call the header function. Headers must be set before you output anything.
See the description from the header() PHP manual page:
Remember that header() must be called before any actual output is
sent, either by normal HTML tags, blank lines in a file, or from PHP.
It is a very common error to read code with include(), or require(),
functions, or another file access function, and have spaces or empty
lines that are output before header() is called. The same problem
exists when using a single PHP/HTML file.
I am not outputting anything so what gives?
I would say that your code is generating an error somewhere. Try setting:
ini_set('display_errors', true);
ini_set('error_reporting', ~0);
In your index.php file as the very first set of commands.
Another possibility is that something somewhere is outputting a space or line return character. You cannot have any output of any kind before you call the header() function.
Possible solutions
There are two ways to fix this.
Use output buffering to catch anything that might be echoed before you have set your headers
Stop the code from outputting anything prematurely although this is a little more brittle
Option 1
To implement solution 1 you would put a call to ob_start() at the very beginning of your code (at the top of your bootstrap file or index.php usually).
Then once all logic has been completed and you are ready to output you would call ob_end_flush() to output everything in the buffer. Usually this would be at the very end of your index.php or bootstrap file.
Option 2
Zend Framework has the following in their coding guidelines to help mitigate the accidental output of new lines and spaces. See http://framework.zend.com/manual/en/coding-standard.php-file-formatting.html#coding-standard.php-file-formatting.general:
For files that contain only PHP code, the closing tag ("?>") is never permitted. It is not required by PHP, and omitting it´ prevents the accidental injection of trailing white space into the response.

Answer 2

When the page I'm using it on redirects a user with the header(); tag. The class is;
That's the problem. You need to put ob_start(); right at the beginning of the file with header();.

Answer 3

That line shouldn't output anything, so that means that output was started because a warning or notice was printed. Fix the problem.
Alternatively, you gave use the wrong source file.

Answer 4

Disable wanrings on php.ini .Those are warnings , if you have access in your php.ini , modify the following
error_reporting = E_ALL & ~E_NOTICE & ~E_DEPRECATED
when in development
display_errors = On
when you'll be in production don't forget to
display_errors = Off
Don't forget to restart apache when you change php.ini
I didn't say to disable errors ,disable only warnings,
Cannot modify header information means you have outputed something before the header.remove all spaces before header();