There was a little doubt at the crucial moment.

There was a small problem at the critical moment. please master [code = PHP] [/code] ession_start () [function. session-start]: Cannotsendsessioncachelimiter-headersalreadysent has such a situation. what is the situation? a little problem occurs at a critical moment.
[Code = PHP] [/code]
Ession_start () [function. session-start]: Cannot send session cache limiter-headers already sent. what is the situation?

Include ("conn. php ");
$ Username = trim ($ _ POST ['username']);
$ Paw = md5 (trim ($ _ POST ['paw']);
$ Post = $ _ POST ['check'];
$ Errmsg = '';
If (! Empty ($ username )){
If (empty ($ username )){
$ Errmsg = 'incomplete data input ';
}
If (empty ($ errmsg )){


If (mysqli_connect_errno ()){
$ Errmsg = "database connection failed! \ N ";
}
Else {

$ SQL = "SELECT * FROM user WHERE username = '$ username' AND pwd =' $ paw '";
$ Result = mysql_query ($ SQL );
If ($ result & mysql_num_rows ($ result)> 0 & $ post =$ _ SESSION [check_pic]) {
Echo "script" alert ('login succeeded '); window. location. href =' ../admin/index. php' script ";

} Else {
Echo "script" alert ('incorrect user name or password and verification code '); window. location. href = 'login1. php' script ";
}

Mysql_free_result ($ result );
Mysql_close ($ db );
}
}
}

?>
This is the code of the program.

------ Solution --------------------