php 验证表单元素是否为空的方法

php验证表单元素是否为空的实例代码：

HTML代码：

<HTML>
<BODY>
<FORM METHOD="POST" ACTION="FormErrorCheck.php">
<H1>Contact Information</H1>
<TABLE>

<TR>
  <TD><B>Nickname:</B></TD>
  <TD><INPUT TYPE="TEXT" NAME="nickname"></TD>
</TR>

<TR>
  <TD><B>First Name:</B></TD>
  <TD><INPUT TYPE="TEXT" NAME="firstname"></TD>
</TR>

<TR>
  <TD><B>Last Name:</B></TD>
  <TD><INPUT TYPE="TEXT" NAME="lastname"></TD>
</TR>

<TR>
  <TD><B>Primary Email:</B></TD>
  <TD><INPUT TYPE="TEXT" NAME="email"></TD>
</TR>

</TABLE>

<BR>
<BR>
<BR>
<INPUT TYPE="SUBMIT" VALUE="Submit">
<BR>
<BR>
<INPUT TYPE="RESET"  VALUE="Clear the Form">

</FORM>
</BODY>
</HTML>

PHP代码：

<?php

  $errors=0;
  $nickname=$_POST['nickname'];
  $firstname=$_POST['firstname'];
  $lastname=$_POST['lastname'];
  $email=$_POST['email'];
  if (!trim($nickname)) {
      echo "<BR><B>Nickname</B> is required.";
     $errors++;
  }
 
  if (!trim($firstname)) {
      echo "<BR><B>First name</B> is required.";
     $errors++;
  }
 
  if (!trim($lastname)) {
      echo "<BR><B>Last name</B> is required.";
      $errors++;
  }
 
  if (!trim($email)) {
      echo "<BR><B>Primary email address</B> is required.";
      $errors++;
  }

  if ($errors > 0)
      echo "<BR><BR><BR>Please use your browser's back button " .
        "to return to the form, and correct error(s)";
 
?>