这个错误在PHP中意味着什么?

这是什么?

这是一些关于在编程PHP时可能遇到的警告、错误和注意事项的答案，而不知道如何修复它们。这也是一个社区维基，所以每个人都被邀请加入和维护这个列表。

为什么会这样?

Questions like "Headers already sent" or "Calling a member of a non-object" pop up frequently on Stack Overflow. The root cause of those questions is always the same. So the answers to those questions typically repeat them and then show the OP which line to change in their particular case. These answers do not add any value to the site because they only apply to the OP's particular code. Other users having the same error cannot easily read the solution out of it because they are too localized. That is sad because once you understood the root cause, fixing the error is trivial. Hence, this list tries to explain the solution in a general way to apply.

我该怎么做呢?

如果您的问题被标记为此问题的副本，请在下面找到您的错误消息并将修复应用于您的代码。答案通常包含进一步的调查链接，以防仅从一般答案中不清楚。

如果您想投稿，请添加您“最喜欢的”错误消息、警告或通知，每个答案一条，简短描述它的含义(即使它只是突出显示手册页的术语)，可能的解决方案或调试方法，以及现有的有价值的问答列表。此外，请随意改进任何现有的答案。

列表

Nothing is seen. The page is empty and white. (also known as White Page/Screen Of Death) Code doesn't run/what looks like parts of my PHP code are output Warning: Cannot modify header information - headers already sent Warning: mysql_fetch_array() expects parameter 1 to be resource, boolean given a.k.a. Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource Warning: [function] expects parameter 1 to be resource, boolean given Warning: [function]: failed to open stream: [reason] Warning: open_basedir restriction in effect Warning: Division by zero Warning: Illegal string offset 'XXX' Warning: count(): Parameter must be an array or an object that implements Countable Parse error: syntax error, unexpected '[' Parse error: syntax error, unexpected T_XXX Parse error: syntax error, unexpected T_ENCAPSED_AND_WHITESPACE Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM Parse error: syntax error, unexpected 'require_once' (T_REQUIRE_ONCE), expecting function (T_FUNCTION) Parse error: syntax error, unexpected T_VARIABLE Fatal error: Allowed memory size of XXX bytes exhausted (tried to allocate XXX bytes) Fatal error: Maximum execution time of XX seconds exceeded Fatal error: Call to a member function ... on a non-object or null Fatal Error: Call to Undefined function XXX Fatal Error: Cannot redeclare XXX Fatal error: Can't use function return value in write context Fatal error: Declaration of AAA::BBB() must be compatible with that of CCC::BBB()' Return type of AAA::BBB() should either be compatible with CCC::BBB(), or the #[\ReturnTypeWillChange] attribute should be used Fatal error: Using $this when not in object context Fatal error: Object of class Closure could not be converted to string Fatal error: Undefined class constant Fatal error: Uncaught TypeError: Argument #n must be of type x, y given Notice: Array to string conversion (< PHP 8.0) or Warning: Array to string conversion (>= PHP 8.0) Notice: Trying to get property of non-object error Notice: Undefined variable or property "Notice: Undefined Index", or "Warning: Undefined array key" Notice: Undefined offset XXX [Reference] Notice: Uninitialized string offset: XXX Notice: Use of undefined constant XXX - assumed 'XXX' / Error: Undefined constant XXX MySQL: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ... at line ... Strict Standards: Non-static method [<class>::<method>] should not be called statically Warning: function expects parameter X to be boolean/string/integer HTTP Error 500 - Internal server error Deprecated: Arrays and strings offset access syntax with curly braces is deprecated

还看到:

这个符号在PHP中是什么意思?

当前回答

致命错误:无法重新声明类[类名]

致命错误:无法重新声明[函数名]

这意味着您要么使用了相同的函数/类名两次，并且需要重命名其中一个，要么是因为您在应该使用require_once或include_once的地方使用了require或include。

在PHP中声明类或函数时，它是不可变的，以后不能用新值声明。

考虑下面的代码:

class.php

<?php

class MyClass
{
    public function doSomething()
    {
        // do stuff here
    }
}

index . php

<?php

function do_stuff()
{
   require 'class.php';
   $obj = new MyClass;
   $obj->doSomething();
}

do_stuff();
do_stuff();

对do_stuff()的第二次调用将产生上述错误。通过将require更改为require_once，我们可以确定包含MyClass定义的文件将只被加载一次，并且可以避免错误。

2012-12-14 13:18:39

其他回答

致命错误:无法重新声明类[类名]

致命错误:无法重新声明[函数名]

这意味着您要么使用了相同的函数/类名两次，并且需要重命名其中一个，要么是因为您在应该使用require_once或include_once的地方使用了require或include。

在PHP中声明类或函数时，它是不可变的，以后不能用新值声明。

考虑下面的代码:

class.php

<?php

class MyClass
{
    public function doSomething()
    {
        // do stuff here
    }
}

index . php

<?php

function do_stuff()
{
   require 'class.php';
   $obj = new MyClass;
   $obj->doSomething();
}

do_stuff();
do_stuff();

对do_stuff()的第二次调用将产生上述错误。通过将require更改为require_once，我们可以确定包含MyClass定义的文件将只被加载一次，并且可以避免错误。

2012-12-14 13:18:39

致命错误:当不在对象上下文时使用$this

$是PHP中的一个特殊变量，不能被赋值。如果在不存在该对象的上下文中访问该对象，则给出此致命错误。

此错误可能发生:

If a non-static method is called statically. Example: class Foo { protected $var; public function __construct($var) { $this->var = $var; } public static function bar () { // ^^^^^^ echo $this->var; // ^^^^^ } } Foo::bar(); How to fix: review your code again, $this can only be used in an object context, and should never be used in a static method. Also, a static method should not access the non-static property. Use self::$static_property to access the static property. If code from a class method has been copied over into a normal function or just the global scope and keeping the $this special variable. How to fix: Review the code and replace $this with a different substitution variable.

相关问题:

致命错误:当不在对象上下文中时使用$this 致命错误:当不在对象上下文中时使用$this 所有“使用$this时不在对象上下文”的问题在Stackoverflow

2012-10-07 15:52:06

注意:未初始化的字符串偏移量:*

顾名思义，当您很可能试图遍历或从具有不存在键的数组中查找值时，就会发生此类错误。

考虑到您正在尝试显示$string中的每个字母

$string = 'ABCD'; 
for ($i=0, $len = strlen($string); $i <= $len; $i++){
    echo "$string[$i] \n"; 
}

上面的例子将生成(在线演示):

A
B
C
D
Notice: Uninitialized string offset: 4 in XXX on line X

并且，一旦脚本完成回显D，你就会得到错误，因为在for()循环中，你已经告诉PHP显示你从'ABCD'的第一个到第五个字符串字符，存在，但由于循环从0开始计数，并在到达4时回显D，它将抛出偏移错误。

类似的错误:

非法字符串偏移量'选项1'

2013-07-13 14:00:02

致命错误:允许的内存大小XXX字节已耗尽(已尝试分配XXX字节)

没有足够的内存来运行脚本。PHP已达到内存限制并停止执行。这个错误是致命的，脚本停止。内存限制的值可以在php.ini文件中配置，也可以使用ini_set('memory_limit'， '128 M');在脚本中(将覆盖php.ini中定义的值)。内存限制的目的是防止一个PHP脚本占用所有可用内存，导致整个web服务器瘫痪。

The first thing to do is to minimise the amount of memory your script needs. For instance, if you're reading a large file into a variable or are fetching many records from a database and are storing them all in an array, that may use a lot of memory. Change your code to instead read the file line by line or fetch database records one at a time without storing them all in memory. This does require a bit of a conceptual awareness of what's going on behind the scenes and when data is stored in memory vs. elsewhere.

如果在脚本没有执行内存密集型工作时发生此错误，则需要检查代码以查看是否存在内存泄漏。memory_get_usage函数是您的朋友。

这个错误在PHP中意味着什么?

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