已定义的未定义变量

Question

我正在尝试创建一个简单的联系表单，但出于某种原因，当我加载 index.php 文件时出现以下错误：

Notice: Undefined variable: emailError in C:\xampp\htdocs\Coming Soon Landing page\index.php on line 105

这是我的代码：（重要的部分是顶部的 PHP 标签，以及 "signup" 部分 ID 中的 php 标签）

<?php

  if (isset($_POST['submit'])) {

      $from = $_POST['email'];
      $to = 'carsonclark2009@gmail.com';
      $subject = 'email sign up';
      $message = 'please sign me up to the mailing list';

      if (!$_POST['email']) {
        $emailError = "Please enter a valid email Address";
      }

  }

?>

<!DOCTYPE html>
  <html lang="en">
    <head>
      <meta charset="utf-8">
      <meta http-equiv="X-UA-Compatible" content="IE=edge">
      <meta name="viewport" content="width=device-width, initial-scale=1">
      <!-- The above 3 meta tags *must* come first in the head; any other head content must come *after* these tags -->
      <title>Landing Page</title>

      <!-- Bootstrap -->
      <link href="css/bootstrap.min.css" rel="stylesheet">
      <!-- Custom CSS -->
      <link rel="stylesheet" href="css/style.css">
      <!-- Fonts -->
      <link rel="stylesheet" href="font-awesome/css/font-awesome.css">
      <link href="https://fonts.googleapis.com/css?family=Just+Another+Hand" rel="stylesheet">
      <link href="https://fonts.googleapis.com/css?family=Amatica+SC" rel="stylesheet">
    </head>
    <body>

      <section id="logo">

        <div class="container">
            <div class="row">

              <div class="col-md-12">
                <img src="img/my-logo.png" class="img-fluid">
              </div>

            </div>
        </div>

      </section>


      <section id="intro">

        <div class="container">
          <div class="row">
            <div class="col-md-12">
              <p>We're working hard, we'll be ready to launch in...</p>
            </div>
          </div>
        </div>

      </section>

        <section id="counter">

        <div class="container">
          <div class="row">
            <div class="col-md-12">
              <div class="countDown"></div>
            </div>
          </div>
        </div>

      </section>

     <section id="icons">

        <div class="container">
          <div class="row">
            <div class="col-md-12">
                <ul class="list-inline">
                    <a href="#"><li class="list-inline-item"><i class="fa twitter fa-twitter-square fa-3x" aria-hidden="true"></i></li></a>
                    <a href="#"><li class="list-inline-item"><i class="fa facebook fa-facebook-square fa-3x" aria-hidden="true"></i></li></a>
                    <a href="#"><li class="list-inline-item"><i class="fa google fa-google-plus-square fa-3x" aria-hidden="true"></i></li></a>
                    <a href="#"><li class="list-inline-item"><i class="fa instagram fa-instagram fa-3x" aria-hidden="true"></i></li></a>
                </ul>
            </div>
          </div>
        </div>

      </section>

      <section id="signup">

        <div class="container">
          <div class="row">

            <div class="col-md-12">
                <form class="form-inline" role="form" method="post" action="#signup">
                    <input type="email" class="form-control form-control-sm" name="email" placeholder="enter your email">
                    <button type="submit" class="btn btn-signup btn-sm" name="submit" value="send">Find out more</button>
                </form>
              <?php echo $emailError; ?>
            </div>

          </div>
        </div>

      </section>

我在页面顶部定义了变量，据我所知（目前尚不清楚）它应该可以工作，但在我点击提交之前我就收到了这个错误。我想知道出了什么问题。非常感谢任何输入。

感谢

Answer 1

您必须在顶部定义 $emailError 变量

 $emailError = "";
 if (isset($_POST['submit'])) {

  $from = $_POST['email'];
  $to = 'carsonclark2009@gmail.com';
  $subject = 'email sign up';
  $message = 'please sign me up to the mailing list';

  if (!$_POST['email']) {
    $emailError = "Please enter a valid email Address";
  }

}

?>

Answer 2

I defined the variable at the top of the page.

if (!$_POST['email']) {
    $emailError = "Please enter a valid email Address";
}

不，您是在 if 语句中定义此变量，可能条件为假。

在 if 语句之外的顶部声明变量或使用此代码：

<?php if (!empty($emailError)) { echo $emailError;} ?>

注意：考虑替换此代码

if (!$_POST['email'])

和

if (!isset($_POST['email']))

Answer 3

只有当 if-condition 为真时，您的变量才会被定义。

您可以定义默认值以防止出错；

<?php

  $emailError = '';

  if (isset($_POST['submit'])) {

      $from = $_POST['email'];
      $to = 'carsonclark2009@gmail.com';
      $subject = 'email sign up';
      $message = 'please sign me up to the mailing list';

      if (!$_POST['email']) {
        $emailError = "Please enter a valid email Address";
      }

  }

?>

Answer 4

而不是

 <?php echo $emailError; ?>

使用这个

 <?php if(isset($emailError)){ echo $emailError;} ?>

或者只是将 @ 符号放在 $emailError 变量之前以禁用该行的错误报告

Answer 5

首先在顶部定义$emailError为空，这样不会给你Undefined Variable通知，比如：

<?php
$emailError = '';
// your code .....

然后您可以进一步检查是否需要设置 $emailError，例如：

<?php 
if(!empty($emailError)){
  echo $emailError; 
}
?>

已定义的未定义变量

Undefined variable that has been defined

php

undefined