php 故障排除“警告：session_start()：无法发送会话缓存限制器 - 标头已发送”
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原文地址: http://stackoverflow.com/questions/10612163/
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Troubleshooting "Warning: session_start(): Cannot send session cache limiter - headers already sent"
提问by user1321271
i am getting Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started aterror
我收到 警告：session_start() [function.session-start]：无法发送会话缓存限制器 - 已发送标头（输出开始时出错
If i submit form data to a different file for processing, it works. But if i submit form data to the same page, it gives this error.
如果我将表单数据提交到不同的文件进行处理，它就可以工作。但是，如果我将表单数据提交到同一页面，则会出现此错误。
please suggst
请建议
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link href="style.css" rel="stylesheet" type="text/css" />
<title>Welcome</title>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$('#nav li').hover(
function () {
//show its submenu
$('ul', this).slideDown(100);
},
function () {
//hide its submenu
$('ul', this).slideUp(100);
}
);
});
</script>
</head>
<body>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td class="header"> </td>
</tr>
<tr>
<td class="menu"><table align="center" cellpadding="0" cellspacing="0" width="80%">
<tr>
<td>
<ul id="nav">
<li><a href="#">Catalog</a>
<ul><li><a href="#">Products</a></li>
<li><a href="#">Bulk Upload</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">Purchase </a>
</li>
<li><a href="#">Customer Service</a>
<ul>
<li><a href="#">Contact Us</a></li>
<li><a href="#">CS Panel</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">All Reports</a></li>
<li><a href="#">Configuration</a>
<ul> <li><a href="#">Look and Feel </a></li>
<li><a href="#">Business Details</a></li>
<li><a href="#">CS Details</a></li>
<li><a href="#">Emaqil Template</a></li>
<li><a href="#">Domain and Analytics</a></li>
<li><a href="#">Courier</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">Accounts</a>
<ul><li><a href="#">Ledgers</a></li>
<li><a href="#">Account Details</a></li>
</ul>
<div class="clear"></div></li>
</ul></td></tr></table></td>
</tr>
<tr>
<td valign="top"><table width="80%" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<td valign="top"><table width="100%" border="0" cellspacing="0" cellpadding="2">
<tr>
<td width="22%" height="327" valign="top"><table width="100%" border="0" cellspacing="0" cellpadding="2">
<tr>
<td> </td>
</tr>
<tr>
<td height="45"><strong>-> Products</strong></td>
</tr>
<tr>
<td height="61"><strong>-> Categories</strong></td>
</tr>
<tr>
<td height="48"><strong>-> Sub Categories</strong></td>
</tr>
</table></td>
<td width="78%" valign="top"><table width="100%" border="0" cellpadding="0" cellspacing="0">
<tr>
<td> </td>
</tr>
<tr>
<td>
<table width="90%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="26%"> </td>
<td width="74%"><h2>Manage Categories</h2></td>
</tr>
</table></td>
</tr>
<tr>
<td height="30">
</td>
</tr>
<tr>
<td>
</td>
</tr>
<tr>
<td>
<table width="49%" align="center" cellpadding="0" cellspacing="0">
<tr><td>
<?php
if (isset($_SESSION['error']))
{
echo "<span id=\"error\"><p>" . $_SESSION['error'] . "</p></span>";
unset($_SESSION['error']);
}
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" enctype="multipart/form-data">
<p>
<label class="style4">Category Name</label>
<input type="text" name="categoryname" /><br /><br />
<label class="style4">Category Image</label>
<input type="file" name="image" /><br />
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
<br />
<br />
<input type="submit" id="submit" value="UPLOAD" />
</p>
</form>
<?php
session_start();
require("includes/conn.php");
function is_valid_type($file)
{
$valid_types = array("image/jpg", "image/jpeg", "image/bmp", "image/gif", "image/png");
if (in_array($file['type'], $valid_types))
return 1;
return 0;
}
function showContents($array)
{
echo "<pre>";
print_r($array);
echo "</pre>";
}
$TARGET_PATH = "images/category";
$cname = $_POST['categoryname'];
$image = $_FILES['image'];
$cname = mysql_real_escape_string($cname);
$image['name'] = mysql_real_escape_string($image['name']);
$TARGET_PATH .= $image['name'];
if ( $cname == "" || $image['name'] == "" )
{
$_SESSION['error'] = "All fields are required";
header("Location: managecategories.php");
exit;
}
if (!is_valid_type($image))
{
$_SESSION['error'] = "You must upload a jpeg, gif, or bmp";
header("Location: managecategories.php");
exit;
}
if (file_exists($TARGET_PATH))
{
$_SESSION['error'] = "A file with that name already exists";
header("Location: managecategories.php");
exit;
}
if (move_uploaded_file($image['tmp_name'], $TARGET_PATH))
{
$sql = "insert into Categories (CategoryName, FileName) values ('$cname', '" . $image['name'] . "')";
$result = mysql_query($sql) or die ("Could not insert data into DB: " . mysql_error());
header("Location: mangaecategories.php");
exit;
}
else
{
$_SESSION['error'] = "Could not upload file. Check read/write persmissions on the directory";
header("Location: mangagecategories.php");
exit;
}
?>
Here is the code for Display
这是显示的代码
<?php
require("includes/conn.php");
$sql = "select CategoryID, CategoryName, FileName, Status from Categories";
$result = mysql_query($sql) or die ("Could not access DB: " . mysql_error());
while ($row = mysql_fetch_assoc($result))
{
echo "<table border='0' cellpadding='10'>";
echo "<tr><td> </td><td>Category ID</td><td>Category Name</td><td>Status</td><td>Edit</td><td>Delete</td></tr>";
echo "<tr><td> <img src=\"images/" . $row['FileName'] . "\" alt=\"\" /> </td>";
echo "<td>". $row['CategoryID'] . "</td>";
echo "<td>". $row['CategoryName'] . "</td>";
echo "<td>". $row['Status']. "</td>";
echo "<td> <a href= 'edit.php?CategoryID=" .$row['id']. "'> Edit </a></td>";
echo "<td> <a href= 'delete.php?CategoryID=" .$row['id']. "'> Edit </a></td>";
echo "</tr> </table>";
}
?>
Nothing is happening here. Please suggest
这里什么也没有发生。请建议
回答by somnath
You will find I have added the session_start() at the very top of the page. I have also removed the session_start() call later in the page. This page should work fine.
您会发现我在页面的最顶部添加了 session_start()。我还删除了页面后面的 session_start() 调用。这个页面应该可以正常工作。
<?php
session_start();
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<link href="style.css" rel="stylesheet" type="text/css" />
<title>Welcome</title>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
$(document).ready(function () {
$('#nav li').hover(
function () {
//show its submenu
$('ul', this).slideDown(100);
},
function () {
//hide its submenu
$('ul', this).slideUp(100);
}
);
});
</script>
</head>
<body>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td class="header"> </td>
</tr>
<tr>
<td class="menu"><table align="center" cellpadding="0" cellspacing="0" width="80%">
<tr>
<td>
<ul id="nav">
<li><a href="#">Catalog</a>
<ul><li><a href="#">Products</a></li>
<li><a href="#">Bulk Upload</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">Purchase </a>
</li>
<li><a href="#">Customer Service</a>
<ul>
<li><a href="#">Contact Us</a></li>
<li><a href="#">CS Panel</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">All Reports</a></li>
<li><a href="#">Configuration</a>
<ul> <li><a href="#">Look and Feel </a></li>
<li><a href="#">Business Details</a></li>
<li><a href="#">CS Details</a></li>
<li><a href="#">Emaqil Template</a></li>
<li><a href="#">Domain and Analytics</a></li>
<li><a href="#">Courier</a></li>
</ul>
<div class="clear"></div>
</li>
<li><a href="#">Accounts</a>
<ul><li><a href="#">Ledgers</a></li>
<li><a href="#">Account Details</a></li>
</ul>
<div class="clear"></div></li>
</ul></td></tr></table></td>
</tr>
<tr>
<td valign="top"><table width="80%" border="0" align="center" cellpadding="0" cellspacing="0">
<tr>
<td valign="top"><table width="100%" border="0" cellspacing="0" cellpadding="2">
<tr>
<td width="22%" height="327" valign="top"><table width="100%" border="0" cellspacing="0" cellpadding="2">
<tr>
<td> </td>
</tr>
<tr>
<td height="45"><strong>-> Products</strong></td>
</tr>
<tr>
<td height="61"><strong>-> Categories</strong></td>
</tr>
<tr>
<td height="48"><strong>-> Sub Categories</strong></td>
</tr>
</table></td>
<td width="78%" valign="top"><table width="100%" border="0" cellpadding="0" cellspacing="0">
<tr>
<td> </td>
</tr>
<tr>
<td>
<table width="90%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td width="26%"> </td>
<td width="74%"><h2>Manage Categories</h2></td>
</tr>
</table></td>
</tr>
<tr>
<td height="30">
</td>
</tr>
<tr>
<td>
</td>
</tr>
<tr>
<td>
<table width="49%" align="center" cellpadding="0" cellspacing="0">
<tr><td>
<?php
if (isset($_SESSION['error']))
{
echo "<span id=\"error\"><p>" . $_SESSION['error'] . "</p></span>";
unset($_SESSION['error']);
}
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" enctype="multipart/form-data">
<p>
<label class="style4">Category Name</label>
<input type="text" name="categoryname" /><br /><br />
<label class="style4">Category Image</label>
<input type="file" name="image" /><br />
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
<br />
<br />
<input type="submit" id="submit" value="UPLOAD" />
</p>
</form>
<?php
require("includes/conn.php");
function is_valid_type($file)
{
$valid_types = array("image/jpg", "image/jpeg", "image/bmp", "image/gif", "image/png");
if (in_array($file['type'], $valid_types))
return 1;
return 0;
}
function showContents($array)
{
echo "<pre>";
print_r($array);
echo "</pre>";
}
$TARGET_PATH = "images/category";
$cname = $_POST['categoryname'];
$image = $_FILES['image'];
$cname = mysql_real_escape_string($cname);
$image['name'] = mysql_real_escape_string($image['name']);
$TARGET_PATH .= $image['name'];
if ( $cname == "" || $image['name'] == "" )
{
$_SESSION['error'] = "All fields are required";
header("Location: managecategories.php");
exit;
}
if (!is_valid_type($image))
{
$_SESSION['error'] = "You must upload a jpeg, gif, or bmp";
header("Location: managecategories.php");
exit;
}
if (file_exists($TARGET_PATH))
{
$_SESSION['error'] = "A file with that name already exists";
header("Location: managecategories.php");
exit;
}
if (move_uploaded_file($image['tmp_name'], $TARGET_PATH))
{
$sql = "insert into Categories (CategoryName, FileName) values ('$cname', '" . $image['name'] . "')";
$result = mysql_query($sql) or die ("Could not insert data into DB: " . mysql_error());
header("Location: mangaecategories.php");
exit;
}
else
{
$_SESSION['error'] = "Could not upload file. Check read/write persmissions on the directory";
header("Location: mangagecategories.php");
exit;
}
?>
回答by Chris B
The answer is above by Ross.
答案在罗斯上面。
Firstly, putting session_start() as the first line of code will mean that you cannot deserialise any objects correctly into session variables.
首先，将 session_start() 作为第一行代码意味着您无法将任何对象正确反序列化为会话变量。
The reason for getting this issue is 99% likely to be trailing spaces at the end of your include files (yes - I know it sounds unlikely but just try it). The offending file is in the error message. I wanted to back up Ross answer which worked for me but this site is counter intuitive.
出现此问题的原因是 99% 的可能是包含文件末尾的尾随空格（是的 - 我知道这听起来不太可能，但请尝试一下）。有问题的文件在错误消息中。我想支持对我有用的罗斯答案，但这个网站是违反直觉的。
IGNORE the nonsense answers. Remove the trailing spaces, newlines etc... and all will be well. ROSS knows what he is talking about. Putting session_start() at the top of your file DOES work but it isnt the correct solution.
忽略无意义的答案。删除尾随空格、换行符等......一切都会好起来的。罗斯知道他在说什么。将 session_start() 放在文件顶部确实有效，但它不是正确的解决方案。
回答by Birb
I had the same issue, but my solution wasn't as obvious as the suggested ones. It turned out that my php-file was written in UTF-8, which caused issues. I copy/pasted the content of the entire file into a new php-file (Notepad++ tells me this is written in ANSI rather than UTF-8), and now it work flawlessly.
我有同样的问题，但我的解决方案并不像建议的那样明显。原来我的 php 文件是用 UTF-8 编写的，这导致了问题。我将整个文件的内容复制/粘贴到一个新的 php 文件中（Notepad++ 告诉我这是用 ANSI 而不是 UTF-8 编写的），现在它可以完美地工作。
回答by somnath
This should solve your problem. session_start() should be called before any character is sent back to the browser. In your case, HTML and blank lines were sent before you called session_start(). Documentation here.
这应该可以解决您的问题。session_start() 应该在任何字符发送回浏览器之前调用。在您的情况下，HTML 和空行是在您调用 session_start() 之前发送的。文档在这里。
To further explain your question of why it works when you submit to a different page, that page either do not use session_start() or calls session_start() before sending any character back to the client! This page on the other hand was calling session_start() much later when a lot of HTML has been sent back to the client (browser).
为了进一步解释当您提交到不同页面时它为什么起作用的问题，该页面要么不使用 session_start() 要么在将任何字符发送回客户端之前调用 session_start()！另一方面，当大量 HTML 被发送回客户端（浏览器）时，这个页面会在很晚之后调用 session_start()。
The better way to code is to have a common header file that calls connects to MySQL database, calls session_start() and does other common things for all pages and include that file on top of each page like below:
更好的编码方法是拥有一个通用头文件，该文件调用连接到 MySQL 数据库、调用 session_start() 并为所有页面执行其他通用操作，并将该文件包含在每个页面的顶部，如下所示：
include "header.php";
This will stop issues like you are having as also allow you to have a common set of code to manage across a project. Something definitely for you to think about I would suggest after looking at your code.
这将阻止您遇到的问题，同时还允许您拥有一组通用的代码来管理整个项目。在查看您的代码后，我会建议您绝对考虑一些事情。
<?php
session_start();
if (isset($_SESSION['error']))
{
echo "<span id=\"error\"><p>" . $_SESSION['error'] . "</p></span>";
unset($_SESSION['error']);
}
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post" enctype="multipart/form-data">
<p>
<label class="style4">Category Name</label>
<input type="text" name="categoryname" /><br /><br />
<label class="style4">Category Image</label>
<input type="file" name="image" /><br />
<input type="hidden" name="MAX_FILE_SIZE" value="100000" />
<br />
<br />
<input type="submit" id="submit" value="UPLOAD" />
</p>
</form>
<?php
require("includes/conn.php");
function is_valid_type($file)
{
$valid_types = array("image/jpg", "image/jpeg", "image/bmp", "image/gif", "image/png");
if (in_array($file['type'], $valid_types))
return 1;
return 0;
}
function showContents($array)
{
echo "<pre>";
print_r($array);
echo "</pre>";
}
$TARGET_PATH = "images/category";
$cname = $_POST['categoryname'];
$image = $_FILES['image'];
$cname = mysql_real_escape_string($cname);
$image['name'] = mysql_real_escape_string($image['name']);
$TARGET_PATH .= $image['name'];
if ( $cname == "" || $image['name'] == "" )
{
$_SESSION['error'] = "All fields are required";
header("Location: managecategories.php");
exit;
}
if (!is_valid_type($image))
{
$_SESSION['error'] = "You must upload a jpeg, gif, or bmp";
header("Location: managecategories.php");
exit;
}
if (file_exists($TARGET_PATH))
{
$_SESSION['error'] = "A file with that name already exists";
header("Location: managecategories.php");
exit;
}
if (move_uploaded_file($image['tmp_name'], $TARGET_PATH))
{
$sql = "insert into Categories (CategoryName, FileName) values ('$cname', '" . $image['name'] . "')";
$result = mysql_query($sql) or die ("Could not insert data into DB: " . mysql_error());
header("Location: mangaecategories.php");
exit;
}
else
{
$_SESSION['error'] = "Could not upload file. Check read/write persmissions on the directory";
header("Location: mangagecategories.php");
exit;
}
?>
回答by Satya
replace session_start();with @session_start();in your code
更换session_start();用@session_start();在你的代码
回答by Altaf Hussain
use ob_start();before session_start();at top of your page like this
像这样在页面顶部使用 ob_start();之前 session_start();
<?php
ob_start();
session_start();
回答by Ross
For others who may run across this - it can also occur if someone carelessly leaves trailing spaces from a php include file. Example:
对于可能遇到此问题的其他人 - 如果有人不小心从 php 包含文件中留下尾随空格，也会发生这种情况。例子：
<?php
require_once('mylib.php');
session_start();
?>
In the case above, if the mylib.php has blank spaces after its closing ?> tag, this will cause an error. This obviously can get annoying if you've included/required many files. Luckily the error tells you which file is offending.
在上面的例子中，如果 mylib.php 在结束 ?> 标签后有空格，这将导致错误。如果您包含/需要许多文件，这显然会令人讨厌。幸运的是，错误告诉您哪个文件有问题。
HTH
HTH
回答by Biswadeep Sarkar
Generally this error arise when we send header after echoing or printing. If this error arise on a specific page then make sure that page is not echoing anything before calling to start_session().
通常，当我们在回显或打印后发送标头时会出现此错误。如果此错误出现在特定页面上，请确保该页面在调用 start_session() 之前没有回显任何内容。
Example of Unpredictable Error:
不可预知的错误示例：
<?php //a white-space before <?php also send for output and arise error
session_start();
session_regenerate_id();
//your page content
One more example:
再举一个例子：
<?php
includes 'functions.php';
?> <!-- This new line will also arise error -->
<?php
session_start();
session_regenerate_id();
//your page content
Conclusion: Do not output any character before calling session_start() or header() functions not even a white-space or new-line
结论：在调用 session_start() 或 header() 函数之前不要输出任何字符，甚至不是空格或换行符
回答by jogesh_pi
use session_start()at the top of the page.
session_start()在页面顶部使用。
for more details please read the link session_start
有关更多详细信息，请阅读链接session_start
回答by Daniel Osei
I was able to solve similar Warning: session_start(): Cannot send session cache limiter - headers already sentby just removing a space in front of the <?phptag.
我可以Warning: session_start(): Cannot send session cache limiter - headers already sent通过删除<?php标签前面的空格来解决类似问题。
It worked.
有效。
