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8.19. Eliminating "headers already sent" Errors

8.19.2. 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); ?>

8.19.3. 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 19.8 describes how to process all the files in a directory.

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.

8.19.4. See Also

Recipe 8.13 discusses output buffering; Recipe 19.8 for processing all files in a directory; documentation on header( ) at http://www.php.net/header.

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