Recipe 20.10. Eliminating


Recipe 20.10. Eliminating "headers already sent" Errors

20.10.1. Problem

You are trying to send an HTTP header or cookie using header( ) or setcookie( ), but PHP reports a "headers already sent" error message.

20.10.2. 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>

20.10.3. 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 directory-by-directory basis. Recipe 24.7 describes how to process all the files in a directory.

Another perfectly legitimate approach to ensuring included files don't have any trailing whitespace is to just leave off the closing ?> tag. If the included file is purely PHP, this method guarantees that you won't have to go back to that file to clean up inadvertent whitespace. See http://www.php.net/manual/en/language.basic-syntax.instruction-separation.php for a bit more discussion of this syntax.

If you don't want to worry about blank lines disrupting the sending of headers, turn on output buffering. Output buffering prevents PHP from immediately sending all output to the client. If you buffer your output, you can intermix headers and body text with abandon. However, it may seem to users that your server takes longer to fulfill their requests since they have to wait slightly longer before the browser displays any output.

20.10.4. See Also

Recipe 8.12 for a discussion of output buffering; Recipe 24.7 for processing all files in a directory; documentation on header( ) at http://www.php.net/header.




PHP Cookbook, 2nd Edition
PHP Cookbook: Solutions and Examples for PHP Programmers
ISBN: 0596101015
EAN: 2147483647
Year: 2006
Pages: 445

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