PHP true 和 'true' 的区别

快问。之间有区别吗

$success = true;

and

$success = 'true';

我知道他们不是'==' 彼此都有，但是使用它们有区别吗？

编辑：我发现在查看 $success 是否为 false 时使用 '===' 而不是 '==' 解决了我的问题。我现在的问题是，我应该在下面的情况下使用字符串，并坚持使用“==”吗？

    $User->ProcessLogin();
$loginsuccess = $User->ProcessLogin();

if ($loginsuccess == true) {    
    echo "<big>Success<big><br />";
        echo "<p>We are now redirecting you to the member area.</p>";
        echo "<meta http-equiv='refresh' content='=2;MyAccountNEW.php' />";
}
elseif ($loginsuccess == false) {
        echo "<span class='sorry'><b>Sorry, your account could not be found.</span></b><div id='shopperlogin'> <img class='shopperlogintext' src='images/shopperlogin.png'>

   <br />

    <form method='post' action='loginNEW.php' name='loginform' id='loginform'>
    <fieldset>
        <label for='username'>Username:</label><input type='text' name='username' id='username' /><br />
        <label for='password'>Password:</label><input type='password' name='password' id='password' /><br />
        <input type='submit' name='login' id='login' value='Login' />
    </fieldset>
    </form></div>";
    }

这是课程的一部分..

    function ProcessLogin() {
    if (!empty($_POST['username']) && !empty($_POST['password'])) {
            $username = mysql_real_escape_string($_POST['username']);
            $password = md5(mysql_real_escape_string($_POST['password']));
            $checklogin = mysql_query("SELECT * FROM users WHERE Username = '".$username."' AND Password = '".$password."'");

                if(mysql_num_rows($checklogin) == 1)
                {
                     $row = mysql_fetch_array($checklogin);
                    $email = $row['EmailAddress'];

                    $_SESSION['Username'] = $username;
                    $_SESSION['EmailAddress'] = $email;
                    $_SESSION['LoggedIn'] = 1;
                    $this->loggedin = true;
                    $success = true;
                }
                else {
                    $success = false;
                }
                return $success;
            }
        }

任何非空字符串的计算结果为 true，空字符串的计算结果为 false。以下脚本可能会给您带来一些启发：

<?php
if('true' == true) {
  echo "'true' == true";
} else {
  echo "'true' != true";
}

echo '<br />';

if('false' == true) {
  echo "'false' == true";
} else {
  echo "'false' != true";
}

echo '<br />';

if('foo' == true) {
  echo "'foo' == true";
} else {
  echo "'foo' != true";
}

echo '<br />';

if('false' == false) {
  echo "'false' == false";
} else {
  echo "'false' != false";
}

echo '<br />';

if('' == true) {
  echo "'' == true";
} else {
  echo "'' != true";
}

echo '<br />';

if('' == false) {
  echo "'' == false";
} else {
  echo "'' != false";
}

?>

这是输出：

'true' == true
'false' == true
'foo' == true
'false' != false
'' != true
'' == false

根据要求，这里还有一些比较 == 和 === 不同值的示例。

<?php
echo "<b>'true' vs. true</b><br />";

if('true' == true) {
  echo "'true' == true<br />";
} else {
  echo "'true' != true<br />";
}

if('true' === true) {
  echo "'true' === true<br />";
} else {
  echo "'true' !== true<br />";
}

echo "<br /><b>'false' vs. true</b><br />";

if('false' == true) {
  echo "'false' == true<br />";
} else {
  echo "'false' != true<br />";
}

if('false' === true) {
  echo "'false' === true<br />";
} else {
  echo "'false' !== true<br />";
}

echo "<br /><b>1 vs. true</b><br />";

if(1 == true) {
  echo "1 == true<br />";
} else {
  echo "1 != true<br />";
}

if(1 === true) {
  echo "1 === true<br />";
} else {
  echo "1 !== true<br />";
}

echo "<br /><b>0 vs. false</b><br />";

if(0 == false) {
  echo "0 == false<br />";
} else {
  echo "0 != false<br />";
}

if(0 === false) {
  echo "0 === false<br />";
} else {
  echo "0 !== false<br />";
}

echo "<br /><b>1 vs. 'true'</b><br />";

if(1 == 'true') {
  echo "1 == 'true'<br />";
} else {
  echo "1 != 'true'<br />";
}

if(1 === 'true') {
  echo "1 === 'true'<br />";
} else {
  echo "1 !== 'true'<br />";
}

echo "<br /><b>empty string '' vs. false</b><br />";

if('' == false) {
  echo "'' == false<br />";
} else {
  echo "'' != false<br />";
}

if('' === true) {
  echo "'' === false<br />";
} else {
  echo "'' !== false<br />";
}

?>

Output:

“真实”与真实

'true' == true
'true' !== true

“假”与真

'false' == true
'false' !== true

1 与真实

1 == true
1 !== true

0 与假

0 == false
0 !== false

1 与“真实”

1 != 'true'
1 !== 'true'

空字符串 '' 与 false

'' == false
'' !== false