致命错误:不能在写上下文中使用函数返回值

这通常发生在直接使用带有empty的函数时。

例子:

if (empty(is_null(null))) {
  echo 'empty';
}

这是因为empty是一个语言结构，而不是一个函数，在5.5之前的PHP版本中，它不能用表达式作为参数调用。在PHP 5.5之前，empty()的参数必须是变量，但在PHP 5.5+中允许任意表达式(例如函数的返回值)。

Empty，尽管它的名字，实际上并不检查一个变量是否为“空”。相反，它检查变量是否存在，或== false。表达式(如示例中的is_null(null))将始终被视为存在，因此这里的empty仅检查它是否等于false。你可以在这里用!替换empty()，例如if (!is_null(null))，或者显式地与false进行比较，例如if (is_null(null) == false)。

相关问题:

致命错误:不能使用函数返回值

HTTP错误500 -内部服务器错误

HTTP状态代码500和典型的Apache或浏览器警告是一个非常广泛的消息。这不是实际的错误。要弄清楚是web服务器配置错误(.htaccess)还是PHP致命错误，你必须查看error.log。

你通常可以在下面找到webservers日志:

/var/log/apache2 on Linux servers, often used for local and virtual hosts. /var/www/_user12345_/logs or similar on shared hosting plans. Usually there's a logs/ directory alongside each htdocs/ folder. C:\xampp\apache\logs\error.log for WAMP/XAMPP distributions of Apache+PHP. Alternatively just use a file search feature to locate anything called "error.log". Or look into your Apache httpd.conf and its ErrorLog directive. /var/log/nginx/nginx_error.log for NGINX. C:\inetpub\logs\LogFiles for IIS. Luckily this is uncommon still, but journalctl -r -u apache2.service could also hold parts of the log on Linux setups.

它是一个文本文件。搜索与错误时间最接近的条目，并使用错误消息的重要部分(从“PHP error:…”到“in line…”)进行进一步的google搜索。

[Mon 22:10] [:error] [pid 12345] [client 127.0.0.1] FastCGI: server "/fcgi/p73" stderr: PHP message:PHP error: Unfiltered inputvariable $_JSON['pokestop_lng'] in filyfile.php on line 845

对于FPM设置，你经常会看到致命的PHP错误。而旧的mod_php(共享主机)配置经常混合警告和通知(通常也值得检查)。

如果没有配置为使用系统或Apache日志机制，您可能还需要查看PHP的error.log。一般来说，保留默认值并启用error_display + error_reporting来显示具体的错误会更简单。HTTP 500全捕获页面不过是PHP死机白屏幕的一个变种。

参见:

500内部服务器错误的php文件，而不是html 我怎么能让PHP显示错误，而不是给我500内部服务器错误 如何在IIS7上显示和记录PHP错误? 如何修复WordPress内部服务器的500个错误

注意:使用未定义的常量XXX -假设“XXX”

或者，在PHP 7.2或更高版本中:

警告:使用未定义的常量XXX -假设“XXX”(这将在未来的PHP版本中抛出错误)

或者，在PHP 8.0或更高版本中:

错误:未定义常量XXX

这种情况发生在代码中使用令牌并且看起来是常量，但没有定义该名称的常量时。

引起此通知的最常见原因之一是没有引用用作关联数组键的字符串。

例如:

// Wrong
echo $array[key];

// Right
echo $array['key'];

另一个常见的原因是变量名前缺少$ (dollar)符号:

// Wrong
echo varName;

// Right
echo $varName;

或者你可能拼写错了其他常数或关键字:

// Wrong
$foo = fasle;

// Right
$foo = false;

当您试图访问由该库定义的常量时，这也可能表明缺少所需的PHP扩展或库。

相关问题:

PHP错误消息“注意:使用未定义的常量”是什么意思?

警告:[function]: failed to open stream: [reason]

当你通过include, require或fopen调用一个文件时，PHP无法找到该文件或没有足够的权限来加载该文件。

这种情况的发生有多种原因:

文件路径错误 文件路径是相对的 包含路径是错误的 权限限制太大 SELinux已生效 还有更多……

一个常见的错误是不使用绝对路径。这可以通过使用完整路径或神奇常数如__DIR__或dirname(__FILE__)轻松解决:

include __DIR__ . '/inc/globals.inc.php';

or:

require dirname(__FILE__) . '/inc/globals.inc.php';

确保使用正确的路径是排除这些问题的一个步骤，这也可能与不存在的文件、文件系统的权限阻止访问或PHP本身的打开basedir限制有关。

快速解决此问题的最佳方法是遵循下面的故障排除清单。

相关问题:

故障排除清单:无法打开流

相关的错误:

警告:open_basedir限制生效

mysql_connect(): user 'name'@'host'拒绝访问

当您连接到无效或缺少凭据(用户名/密码)的MySQL/MariaDB服务器时，会出现此警告。所以这通常不是代码问题，而是服务器配置问题。

See the manual page on mysql_connect("localhost", "user", "pw") for examples. Check that you actually used a $username and $password. It's uncommon that you gain access using no password - which is what happened when the Warning: said (using password: NO). Only the local test server usually allows to connect with username root, no password, and the test database name. You can test if they're really correct using the command line client: mysql --user="username" --password="password" testdb Username and password are case-sensitive and whitespace is not ignored. If your password contains meta characters like $, escape them, or put the password in single quotes. Most shared hosting providers predeclare mysql accounts in relation to the unix user account (sometimes just prefixes or extra numeric suffixes). See the docs for a pattern or documentation, and CPanel or whatever interface for setting a password. See the MySQL manual on Adding user accounts using the command line. When connected as admin user you can issue a query like: CREATE USER 'username'@'localhost' IDENTIFIED BY 'newpassword'; Or use Adminer or WorkBench or any other graphical tool to create, check or correct account details. If you can't fix your credentials, then asking the internet to "please help" will have no effect. Only you and your hosting provider have permissions and sufficient access to diagnose and fix things. Verify that you could reach the database server, using the host name given by your provider: ping dbserver.hoster.example.net Check this from a SSH console directly on your webserver. Testing from your local development client to your shared hosting server is rarely meaningful. Often you just want the server name to be "localhost", which normally utilizes a local named socket when available. Othertimes you can try "127.0.0.1" as fallback. Should your MySQL/MariaDB server listen on a different port, then use "servername:3306". If that fails, then there's a perhaps a firewall issue. (Off-topic, not a programming question. No remote guess-helping possible.) When using constants like e.g. DB_USER or DB_PASSWORD, check that they're actually defined. If you get a "Warning: Access defined for 'DB_USER'@'host'" and a "Notice: use of undefined constant 'DB_PASS'", then that's your problem. Verify that your e.g. xy/db-config.php was actually included and whatelse. Check for correctly set GRANT permissions. It's not sufficient to have a username+password pair. Each MySQL/MariaDB account can have an attached set of permissions. Those can restrict which databases you are allowed to connect to, from which client/server the connection may originate from, and which queries are permitted. The "Access denied" warning thus may as well show up for mysql_query calls, if you don't have permissions to SELECT from a specific table, or INSERT/UPDATE, and more commonly DELETE anything. You can adapt account permissions when connected per command line client using the admin account with a query like: GRANT ALL ON yourdb.* TO 'username'@'localhost'; If the warning shows up first with Warning: mysql_query(): Access denied for user ''@'localhost' then you may have a php.ini-preconfigured account/password pair. Check that mysql.default_user= and mysql.default_password= have meaningful values. Oftentimes this is a provider-configuration. So contact their support for mismatches. Find the documentation of your shared hosting provider: e.g. HostGator, GoDaddy, 1and1, DigitalOcean, BlueHost, DreamHost, MediaTemple, ixWebhosting, lunarhosting, or just google yours´. Else consult your webhosting provider through their support channels. Note that you may also have depleted the available connection pool. You'll get access denied warnings for too many concurrent connections. (You have to investigate the setup. That's an off-topic server configuration issue, not a programming question.) Your libmysql client version may not be compatible with the database server. Normally MySQL and MariaDB servers can be reached with PHPs compiled in driver. If you have a custom setup, or an outdated PHP version, and a much newer database server, or significantly outdated one - then the version mismatch may prevent connections. (No, you have to investigate yourself. Nobody can guess your setup).

更多的引用:

mysql服务器错误:mysql用户无法访问root用户 mysql_connect():拒绝访问 mysql_select_db()拒绝访问用户" @'localhost'(使用密码:NO) PHPMyAdmin拒绝用户“root”@“localhost”的访问

顺便说一句，你可能不想再使用mysql_*函数了。新来者经常迁移到mysqli，然而这也一样乏味。相反，阅读PDO和准备好的语句。 $db =新PDO("mysql:主机=localhost;dbname=testdb"， "用户名"，"密码");

代码不运行/我的PHP代码的某些部分被输出

如果你的PHP代码没有任何结果，或者你在网页中看到你的PHP源代码输出的部分文字，你可以很确定你的PHP实际上没有被执行。如果在浏览器中使用“查看源代码”，则可能会看到完整的PHP源代码文件。因为PHP代码嵌入在<?php ?>标记时，浏览器将尝试将它们解释为HTML标记，结果可能看起来有些混乱。

要真正运行PHP脚本，您需要:

执行脚本的web服务器 将文件扩展名设置为.php，否则web服务器不会将其解释为* 通过web服务器访问你的。php文件

*除非你重新配置，否则一切都可以配置。

最后一点尤其重要。只需双击该文件，就可以在浏览器中使用如下地址打开它:

file://C:/path/to/my/file.php

这完全绕过了您可能正在运行的任何web服务器，并且文件没有得到解释。你需要在你的web服务器上访问文件的URL，可能是这样的:

http://localhost/my/file.php

您可能还想检查是否使用了短的打开标记<?而不是<?php和您的php配置已关闭短打开标记。

还可以看到PHP代码没有被执行，而是代码显示在页面上