The headers_sent() function checks if / where the HTTP headers have been sent.
This function returns TRUE if headers has been sent or FALSE if not.
|file,line||Optional. If the file and line parameters are set, headers_sent() will put the PHP source file name and line number where output started in the file and line variables|
Note: You can't add more header lines using header() once the header block has already been sent.
Note: The optional file and line parameters where added in PHP 4.3.
Using the optional file and line parameters:
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