该如何清空$_POST里的数据？-PHP Tutorial-php.cn

该如何清空$_POST里的数据？

WBOY

Release： 2016-06-23 14:06:34

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试写了一个登陆界面，还没有完成，测试的时候发现问题。$_POST里的值不会清空，每输入一次用户名，$_POST里面就多一个用户名，后果就是第一次错误输入的话，就无法再正确输入用户名。。。除非浏览器刷新页面。。。

<!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 content="en-us" http-equiv="Content-Language" /><meta content="text/html; charset=utf-8" http-equiv="Content-Type" /><title>Welcome back</title><style type="text/css">.auto-style2 {	text-align: center;}.auto-style1 {	font-size: 36pt;	text-align: left;}.auto-style4 {	font-family: Broadway;	font-size: xx-large;}</style></head><body><table align="center" style="width: 100%">	<tr>		<td>		<div class="auto-style2">			<table align="center" style="width: 100%">				<tr>					<td class="auto-style1">Welcome back</td>					<td>					<img     style="max-width:90%" src="logo.jpg" style="float: right"  style="max-width:90%" / alt="该如何清空$_POST里的数据？" ></td>				</tr>			</table>		</div>		<hr />				<p class="auto-style4">Log in:</p>		<form action="login.php" method="post" style="height: 213px">			<div class="auto-style2">				<table style="width: 100%">					<tr>						<td class="auto-style2">User Name:</td>					</tr>					<tr>						<td class="auto-style2">							<input name="user_name" type="text" value="								<?php 									if(isset($_POST['user_name']))									{										print htmlspecialchars($_POST['user_name']);									}								?>							"/>						</td>					</tr>					<tr>						<td class="auto-style2">Password:</td>					</tr>					<tr>						<td class="auto-style2">						<input name="password" type="password" /></td>					</tr>				</table>				<br />				<br />				<input name="submit" type="submit" value="Sign in" /></div>		</form>		</td>	</tr></table><?phprequire_once 'connectDB.php';print '<style type = "text/css" media = "screen">.error {color: red;}</style>';if($_SERVER['REQUEST_METHOD']=='POST'){	$problem = false;	$login = false;	if(empty($_POST['user_name']))	{		$problem = true;		print '<p class = "error">Please enter your user name!</p>';	}	if(empty($_POST['password']))	{		$problem = true;		print '<p class = "error">Please enter a password</p>';	}	if(!$problem)	{		$user = trim(stripslashes($_POST['user_name']));		$pwd = trim(stripslashes($_POST['password']));		$user = mysql_real_escape_string($user);		$pwd = mysql_real_escape_string($pwd);				$q = "SELECT * FROM USER WHERE USER_NAME = '$user' and PASSWORD = '$pwd'";				echo $q;				$result = mysql_query($q);				if(!$result || mysql_num_rows($result) == 0)		{			print '<p class = "error">Wrong Username or Password.</p>';		}		else		{			$row = mysql_fetch_array($result);			$id = $row['USER_ID'];			$name = $row['USER_NAME'];			echo "User ID is ".$id;						session_start();			$_SESSION['$id'] = $id;						//clear the POST array				$_POST = array();   //网上找来的办法， 但貌似不管用					}			}	else	{		print '<p class = "error">Please try again!</p>';	}		}?></body></html>

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请高手帮忙解决一下，感激不尽

回复讨论(解决方案)

                            <input name="user_name" type="text" value="                                <?php                                     if(isset($_POST['user_name']))                                    {                                        print htmlspecialchars($_POST['user_name']);                                    }                                ?>                            "/>

Copy after login

改为

                            <input name="user_name" type="text" value="<?php                                     if(isset($_POST['user_name']))                                    {                                        print htmlspecialchars($_POST['user_name']);                                    }                                ?>"/>

Copy after login

即可
是 value 中的空格和回车换行符在作怪

PHP code?12345678 谢谢版主大神。小弟刚刚学习php和网页制作，大神是否能解释一下，空格和回车符作怪的原因吗？

input type=text 是单行文本编辑器
如果你给他的是多行的文本，那么只有第一行可以被编辑。这就是你遇到的问题的原因

怎么会有这种事？？？

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我是来学习的

可能是你post 赋值时有问题,post 的值只会覆盖上一个,怎么会附加呢..