duanfangbunao36970 2013-08-16 09:02
浏览 45

怎么来的(' - '== 0)===是真的吗?

I was working here with some exploded string walks:

array_walk($data, function(&$value)
    // Transform numerics into appropriate type numbers
    if (is_numeric($value))
        $value = substr_count($value, '.') == 1 ? (float) $value : (int) $value;

    // Transform dashes into nulls
    if ($value == '-')
        $value = null;

to transform values into their appropriate types, and some special character handling.

Where I stumbled upon an interesting, huh, bug?

The Bug

I was amazed, that each entry, that had it's initial value as string(1) '0' ended up being a null.

At first, I thought that the problem relies in (float) and (int) typecasts, though, after debugging:

var_dump((float) '0', (int) '0');

I saw that's not the case, getting the expected result:


It took me a while, to attempt to debug the, what at the moment appeared to be an obvious, weak type check, but, once I did, I was shocked:

var_dump('-' == 0);

The above expression appears to be:


Now, while writing, I thought I should debug some more, so:

var_dump( '=' == 0 );
var_dump( 'What a lovely nonsense?' == 0 );
var_dump( 0 == 'DAFUQ?' ); // maybe it's because of order? It's PHP, world of miracles, you know...

And, every expression listed above is bool(true).

Okay, maybe that's because internally, mystically PHP casts the expression into a (bool)?

var_dump( (bool) '-' == 0 );



So, so, so...

I made a test-case here: http://codepad.org/smiEvsDj
The problem exists in 5.2.5 (codepad), also in 5.4.3 (friend) and also in 5.4.17 (my actual environment).

What is the reason behind this feature / bug / what-the-F-actually-is-this?

  • 写回答

2条回答 默认 最新

  • douli6605 2013-08-16 09:12

    You have stumbled upon one of the major complaints that people have about PHP as a language: The fact that the "==" operator is not transitive.

    Any string "foo" == TRUE, because the PHP people wanted this to work:

    if ($string) {
        // do something if $string is set

    Yet, converting a string to a number (which PHP always tries to do when you use "=="), "foo" == 0!

    Of course, TRUE != 0. That is a major pain when dealing with PHP, it's not logical, but it's reality.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?



  • ¥15 Power BI 里面 帕累托图突出显示前20
  • ¥50 用预估矫正法,分数阶微分方程组传染病的最优控制代码怎么写
  • ¥15 画个数据流程图,手画也行
  • ¥60 AS自带模拟器AVD Root 和 Xposed安装
  • ¥15 Esp32的microPython设备中main.py文件无法开机自启动
  • ¥30 哪位搞Android的编程师可以帮我远程一下,悬赏30元
  • ¥15 solidity部署上合约,可以mint,也继承接口了,在区块链也不显示代币名字
  • ¥15 讨论 博士论文交互项怎么讨论?
  • ¥50 在集成BiLSTM和GCN模型时遇到了问题
  • ¥33 集成BiLSTM模型和GCN模型时,前模型的输出不匹配后模型的输入