PHP echo 未正确返回 <div>

Question

有人可以告诉我为什么该<?php echo $userPasswordError; ?>行不返回任何内容（空），而不是<div class="invalid-feedback">Too long.</div>当我使用以下代码输入包含超过 1 个字符的密码时？如果我改变这一行：$userPasswordError = '<div class="invalid-feedback">Too long.</div>';有了这个$userPasswordError = 'Too long.';，就可以了！输出是“太长”。<?php$user = $userPassword = '';$userError = $userInvalid = $userPasswordError = $userPasswordInvalid = '';$isvalidOrInvalidUser = $isvalidOrInvalidUserPassword = '';if ($_SERVER["REQUEST_METHOD"] == "POST") {  // Verify username.  if (!empty($_POST["user"])) {    if (strlen($_POST["user"]) <= 32) {      $user = $_POST["user"];      $userError = '<div class="valid-feedback">Correct.</div>';      $isvalidOrInvalidUser = 'is-valid';    }    else {      $userInvalid = $_POST["user"];      $userError = '<div class="invalid-feedback">Too long.</div>';      $isvalidOrInvalidUser = 'is-invalid';    }  }  else {    $userError = '<div class="invalid-feedback">Please, add username.</div>';    $isvalidOrInvalidUser = 'is-invalid';  }  // Verify password.  if (!empty($_POST["userpassword"])) {    if (strlen($_POST["userpassword"]) <= 1) {      $userPassword = $_POST["userpassword"];      $userPasswordError = '<div class="valid-feedback">Correct.</div>';      $isvalidOrInvalidUserPassword = 'is-valid';    }    else {      $userPasswordInvalid = $_POST["userpassword"];      $userPasswordError = '<div class="invalid-feedback">Too long.</div>';      $isvalidOrInvalidUserPasword = 'is-invalid';    }  }  else {    $userPasswordError = '<div class="invalid-feedback">Please, add password.</div>';    $isvalidOrInvalidUserPassword = 'is-invalid';  }}

Answer 1

我终于知道为什么了。

  $userPasswordError = '<div class="invalid-feedback">Too long.</div>';

  $isvalidOrInvalidUserPasword = 'is-invalid';

的变量名isvalidOrInvalidUserPasword错误，应该是$isvalidOrInvalidUserPassword（缺少sat密码）。

如果输入没有 class is-invalid，错误消息将不可见！

希望这可以帮助！