提交之前表单验证

Question

只是一个快速的，我似乎无法发现，并希望其他人可以发现我的错误，我有一些PHP编写的字符串验证代码，我遇到的问题是表单似乎在打开提交按钮后立即验证“customerfname”字段，只要表单打开，即使在按下提交按钮之前也会显示错误“请输入您的名字”。有谁能发现我的错误？

<?php 

$flag = false; 
$badchar = ""; 
$string = $_POST["customerfname"]; 
$string = trim($string); 
$length = strlen($string); 
$strmsg = ""; 

if (isset($_POST["submit"])) { 
    if ($length == 0) { 
     $strmsg = '<span class="error"> Please enter your first name</span>'; 
     $flag = true; 
     $valid = false;} 
    else if ($length > 30) { 
     $strmsg = '<span class="error"> Can not enter more than 30 characters</span>'; 
     $flag = true; 
     $valid = false; 
     } 
else{ 
    for ($i=0; $i<$length;$i++){ 
     $c = strtolower(substr($string, $i, 1)); 
     if (strpos("abcdefghijklmnopqrstuvwxyz-", $c) === false){ 
      $badchar .=$c; 
      $flag = true; 
      $valid = false; 
     } 
    } 
    if ($flag) { 
     $strmsg = '<span class="error"> The field contained the following invalid characters: '.$badchar.'</span>';} 
    } 
    if (!$flag) { 
     $valid = true; 
    } 
} 

?> 

<form method="POST" action="<?php echo $_SERVER["PHP_SELF"];?>" id="custinfo"> 

<td><label for="customerfname">Customer First Name: </label></td> 
<td><input type="text" id="customerfname" name="customerfname" size=50/><?php echo $strmsg; ?></td> 

<p><input type="submit" name="submit" value="Save Data"/>&nbsp;<input type="reset" value="Clear Form" /> 

</form> 

Answer 1

<?php 
$flag = false; 
$badchar = ""; 
$strmsg = ""; 
if(isset($_POST['customerfname'])) 
{ 
$string = $_POST["customerfname"]; 
$string = trim($string); 
$length = strlen($string); 
} 
if (isset($_POST["submit"])) { 
if ($length == 0) { 
$strmsg = '<span class="error"> Please enter your first name</span>'; 
$flag = true; 
$valid = false;} 
else if ($length > 30) { 
$strmsg = '<span class="error"> Can not enter more than 30 characters</span>'; 
$flag = true; 
$valid = false;} 
else { 
for ($i=0; $i<$length;$i++){ 
    $c = strtolower(substr($string, $i, 1)); 
    if (strpos("abcdefghijklmnopqrstuvwxyz-", $c) === false){ 
     $badchar .=$c; 
     $flag = true; 
     $valid = false; 
    } 
} 
if ($flag) { 
    $strmsg = '<span class="error"> The field contained the following invalid characters: '.$badchar.'</span>';} 
} 
if (!$flag) { 
    $valid = true;} 
    var_dump($valid); 
} 

?> 

<form method="POST" action="" id="custinfo"> 

<td><label for="customerfname">Customer First Name: </label></td> 
<td><input type="text" id="customerfname" name="customerfname" size=50/><?php echo $strmsg; ?></td> 
<td><input type="submit" name="submit" /></td> 

</form> 

Answer 2

您应该添加一个提交按钮与“提交”作为名称，并将所有关于POST请求的线下您的if (isset($_POST["submit"]))

这里是工作（还有很多东西要改善，但这是一个开始）你的代码版本：

<?php 

$flag = false; 
$badchar = ""; 
$strmsg = ""; 

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

    $string = (isset($_POST["customerfname"])) ? $_POST["customerfname"] : ''; // if customerfname wasn't sent, $string will be empty 
    $string = trim($string); 
    $length = strlen($string); 

    if ($length == 0) { 
     $strmsg = '<span class="error"> Please enter your first name</span>'; 
     $flag = true; 
     $valid = false; 
    } 
    else if ($length > 30) { 
     $strmsg = '<span class="error"> Can not enter more than 30 characters</span>'; 
     $flag = true; 
     $valid = false; 
    } 
    else { 
     for ($i=0; $i<$length;$i++) { 
       $c = strtolower(substr($string, $i, 1)); 
       if (strpos("abcdefghijklmnopqrstuvwxyz-", $c) === false) { 
        $badchar .=$c; 
        $flag = true; 
        $valid = false; 
       } 
     } 
     if ($flag) { 
      $strmsg = '<span class="error"> The field contained the following invalid characters: '.$badchar.'</span>'; 
     } 
    } 
    if (!$flag) { 
     $valid = true; 
    } 
} 

?> 

<form method="POST" action="<?php echo $_SERVER["PHP_SELF"];?>" id="custinfo"> 

<td><label for="customerfname">Customer First Name: </label></td> 
<td><input type="text" id="customerfname" name="customerfname" size=50/><?php echo $strmsg; ?></td> 
<td><input type="submit" name="submit"></td> 

</form>