ERROR-PHP hint "headers already sent by" what's going on?

Error message:
Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 9

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 10

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 28

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 29

Approximate code:

   
 ";                } else {echo "Login failed!";            echo "Please check that your user name or password is filled in correctly";            }} else {echo "Login failed!";        echo "Please check if your user name or password is empty"; }}?>

The error is roughly this location:
Setcookie (' username ', ' $username ', Time () +31536000, '/');
Setcookie (' Logset ', ' OK ', Time () +31536000, '/');

Reply content:

Error message:
Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 9

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 10

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 28

Sae_warning:cannot Modify header Information-headers already sent by (output started at/data1/www/htdocs/345/leank/1/b BS/LOGIN.PHP:15) in bbs/login.php on line 29

Approximate code:

   
 ";                } else {echo "Login failed!";            echo "Please check that your user name or password is filled in correctly";            }} else {echo "Login failed!";        echo "Please check if your user name or password is empty"; }}?>

The error is roughly this location:
Setcookie (' username ', ' $username ', Time () +31536000, '/');
Setcookie (' Logset ', ' OK ', Time () +31536000, '/');

Because in the Setcookie before the output of something caused, see the code seems to be the output of space, the middle of the

?>  
 
  
get rid of it.
                                        
                                    
Dear. Remember to save the file to UTF-8 without BOM format every time you finish writing the program. Otherwise it would be easier to say the wrong thing.
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