PHP 错误无法发送会话缓存限制器 - 标头已发送

Question

Hello I have three PHP codes where one page I have is of index.php where I am scanning the username and password from the user and then sending it to another file userlogin_process.php where I am first starting the session and then I am matching the scanned values with the database and if they match I am storing them into session variable but it shows me 2 warnings on that page Cannot send session cache limiter - headers already sent and last page I have is of user_session.php where I am locating the user to the home page of the website.

index.php

session_start();
<form method="post" action="userlogin_process.php">
<div class="p">User Login</div>  
<table style="margin-top:5%;margin-left:12%;">
<tr><td> <label style="font-size:16px"> UserName :</label></td></tr>
<tr><td><input class="input" type="text" name="username" placeholder="FirstName"/></td></tr>
<tr><td><label style="font-size:16px">Password :</label></td></tr>
<tr><td><input class="input" type="password" name="userpass" placeholder="Mobile No"/></td></tr>
<tr><td>&nbsp;</td></tr>
<tr><td align="center"><input class="button" type="submit" name="usersubmit" value="Login"/></td></tr>
</table>
</form>

user_loginprocess.php

<?php 
session_start();
include("db.php");
$uname = $_POST['username'];
$upass = $_POST['userpass'];
echo $uname;
echo $upass;
$sql = mysql_query("select id,fname,mobile from user where fname='$uname'") or die(mysql_error());
$count = mysql_num_rows($sql);
if ($count > 0){
while($row = mysql_fetch_array($sql)){
$id = $row['id'];
$fname = $row['fname'];
$mobile = $row['mobile'];
}
}
if( $uname == $fname && $upass == $mobile ){
$_SESSION['uid'] = $id; 
$_SESSION['username'] = $fname;
$_SESSION['usermobile'] = $mobile;
$_SESSION['login'] = "yes";
header('location:user_session.php');
}
else{       
header('location:index.php?msg=incorrect');
} 
?> 

user_sesssion.php

<?php 
 session_start();
if( isset($_SESSION['login']) == "yes"){
header('location:user_detail.php?pageno=1');
} 
else{   
header('location:index.php?msg=login');
}
 ?>

Answer 1

First thing i can see is that you use session_start() multiple times. as you can see it in their docs that will not create any harm but it may throw an error or warnings.. so it is better to stick to use only once.

Second please use mysqli_* docs since my_sql is deprecated. or PDO .

and this part looks off::

session_start();
<form method="post" action="userlogin_process.php">

it should be:

<?php session_start(); ?>
<form method="post" action="userlogin_process.php">

but either way is wrong since session should be stared in top of the page. and last try to fix all those small mistakes, it may work or throw another error, which in either case is good, since is moving forwards :)

Answer 2

To stop sending header very early it is good to buffer output and send at the end of script. For this turn on buffering in php.ini.

output_buffering = On