如何使单选按钮、选择框和复选框成为表单中的必需字段

<form action="" method="post">  
     <ul id="register">
        <li>
          <input type="text" name="first_name" placeholder="First Name">
        </li>
        <li>
        <input type="text" name="last_name" placeholder="Last Name">
        </li>
       <li>
        <input type="email" name="email" placeholder="Email"><br><br>
        </li>
        <li>
      <input type="password" name="password" placeholder="Password">
        </li>
        <li>
        <input type="radio" name="sex" value="male">Male
        <input type="radio" name="sex" value="female">Female
        </li>
        <li>
        Birthday:
            <select name="month">
                    <option value="January">January</option>
                    //all the other month options
                </select>
                <select name="day">
                    <option value="1">1</option>
                    //all the other days of the month
                </select>
                <select name="year">
                    <option value="2013">2013</option>
                    //ton of year options here
                </select><br><br>
            </li>
            <li>
                <input type="checkbox" name="terms_of_service" value="termsofservice">Terms of Service<br><br>
            </li>
            <li>
                <input type="submit" name="registrationform" value="Sign up">
            </li>
        </ul>
    </form>
    <?php

    if (empty($_POST) === false) {
        $required_fields = array('first_name', 'last_name', 'email', 'password', 'sex', 'birthday', 'terms_of_service');
        foreach ($_POST as $key=>$value) {
            if (empty($value) && in_array($key, $required_fields) === true) {
                $errors[] = 'You didn''t fill in all of the categories.';
                break 1;
            }
        }
    }
    print_r($errors);

    ?>

try this.

 if(isset($_POST['registrationform'])){
       $required_fields = array( /* all required fields including radio, select and 
checkboxes  as associative array with key as actual name and value as field name */);
       foreach ( $required_fields as $key=>$value) {
             if (!isset($_POST[$value]) || $_POST[$value]=='') {
                  $errors[$value] = $key." is required";
                }
       }
       print_r($errors);
    }

服务器端和客户端验证:

服务器端验证在服务器端处理。有些数据无法在客户端进行验证，必须在服务器端进行验证。例如:数据库中两个日期之间的日期。

客户端验证在提交表单之前由客户端处理。使用客户端验证的优点是它减少了网络流量，因为验证是在客户端机器本身中处理的。例如电子邮件、数字、日期等

如果你想要服务器端验证(在PHP中)，你需要写这样的条件:

if($_SERVER['REQUEST_METHOD'] == 'POST'){
    $error_msg = array();
    if(!isset($_POST['your_radio_button_name'])){
        $error_msg[] = "Enter the required fields";
    }
    if(!isset($_POST['your_checkbox_button_name'])){
        $error_msg[] = "Enter the required fields";
    }
    if(!isset($_POST['your_select_box_name'])){
        $error_msg[] = "Enter the required fields";
    }
    if(isset($error_msg) && count($error_msg) == 0){
        // do some form processing
    }
    else{
        // redirect to the form again.
    }
} 

阅读更多关于php表单验证的内容:

http://phpmaster.com/form-validation-with-php/

如果你想要客户端验证，那么有很多选项可供选择:

查看以下文章:

http://www.jeasyui.com/tutorial/form/form3.php

希望对你有帮助。

Try This:

<form action="" method="post">  
    <ul id="register">
        <li><input type="text" name="first_name" placeholder="First Name"></li>
        <li><input type="text" name="last_name" placeholder="Last Name"></li>
        <li><input type="email" name="email" placeholder="Email"><br><br></li>
        <li><input type="password" name="password" placeholder="Password"></li>
        <li>
            <input type="radio" name="sex" value="male">Male
            <input type="radio" name="sex" value="female">Female
        </li>
        <li>
            Birthday:
            <select name="month">
                <option value="">Choose</option>
                <option value="January">January</option>
                <option value="February">February</option>
            </select>
            <select name="day">
                <option value="">Choose</option>
                <option value="1">1</option>
                <option value="2">2</option>
            </select>
            <select name="year">
                <option value="">Choose</option>
                <option value="2012">2012</option>
                <option value="2013">2013</option>
            </select><br><br>
        </li>
        <li><input type="checkbox" name="terms_of_service" value="termsofservice">Terms of Service<br><br></li>
        <li><input type="submit" name="registrationform" value="Sign up"></li>
    </ul>
</form>
<?php
if (!empty($_POST)) {
    $required_fields = array('first_name', 'last_name', 'email', 'password', 'sex', 'month', 'day', 'year', 'terms_of_service');
    foreach ($required_fields as $value) {
        if (empty($_POST["$value"])) {
            $errors .= "$value is required<br>";
        }
    }            
    echo $errors;
}
?>

Ultimate的答案是完美的，正是您所需要的。

我将解释什么是服务器验证和本地验证。

本地验证是当你在html代码或javascript中检查输入时。是快速的，因为它是在浏览器检查。但是任何访问你的页面的人都可以用一点技术技巧来禁用这种验证。

服务器验证是当您检查php代码中的输入时。(<?php and ?>之间的代码)。然后在服务器中检查它。因此，任何访问您的页面的人都将而不是能够禁用该验证。

无论如何，我建议两者都使用。因为本地验证很快，而服务器验证很安全。

要添加本地验证，这个链接会很好地解释它:http://www.w3schools.com/html5/att_input_required.asp

[确保你在你的代码的第一部分的doctype设置使用html5:

<!DOCTYPE html>
<html>
<head>
...blablabalblabla more html code...

然后你的HTML与验证将导致类似这样的东西:

<form action="" method="post">  
 <ul id="register">
    <li>
      <input type="text" name="first_name" placeholder="First Name" required="required">
    </li>
    <li>
    <input type="text" name="last_name" placeholder="Last Name" required="required">
    </li>
   <li>
    <input type="email" name="email" placeholder="Email" required="required"><br><br>
    </li>
    <li>
  <input type="password" name="password" placeholder="Password" required="required">
    </li>
    <li>
    <input type="radio" name="sex" value="male" required="required">Male
    <input type="radio" name="sex" value="female" required="required">Female
    </li>
    <li>
...

这就是html5本地验证