问题描述

我真的很困惑为什么这个操作有效.有人能解释一下吗?

I'm really confused as to why this operation works. Can someone explain it?

$test1 = "d85d1d81b25614a3504a3d5601a9cb2e";
$test2 = "3581169b064f71be1630b321d3ca318f";

if ($test1 == 0)
  echo "Test 1 is Equal!?";
if ($test2 == 0)
  echo "Test 2 is Equal!?";

// Returns: Test 1 is Equal!?

为了澄清起见，我试图将字符串 "0" 与 $test 变量进行比较.我已经知道要修复我可以将 ""s

For clarification, I am trying to compare the string "0" to the $test variables. I already know to fix the code I can just enclose (as I should have) the 0 in ""s

我想知道这是 PHP 错误、服务器错误还是某种有效操作.根据http://us3.php.net/types.comparisons，这不应该 成功了.

I'm wondering if this is a PHP bug, a server bug, or somehow a valid operation. According to http://us3.php.net/types.comparisons this should not have worked.

从头开始，显然它确实提到字符串和 0 之间的松散比较是正确的.但我还是不知道为什么.

Scratch that, apparently it does mention that Loose comparisons between string and 0 is true. But I still don't know why.

编辑 2: 我已经修改了我的问题，为什么 "3581169b064f71be1630b321d3ca318f" 的 $test2 值不起作用?

Edit 2: I've revised my question, why does the $test2 value of "3581169b064f71be1630b321d3ca318f" not work?

推荐答案

来自 PHP 手册:

字符串转数字

当一个字符串在一个数字上下文，结果值和类型确定如下.

When a string is evaluated in a numeric context, the resulting value and type are determined as follows.

该字符串将被评估为浮动，如果它包含任何字符."、e"或E".否则，它将被评估为整数.

The string will be evaluated as a float if it contains any of the characters '.', 'e', or 'E'. Otherwise, it will be evaluated as an integer.

值由初始值给出字符串的一部分.如果字符串以有效的数字数据开头，这将是使用的值.否则，值将为 0(零).有效数字data 是一个可选的符号，后跟一位或多位数字(可选包含小数点)，然后通过一个可选的指数.指数是一个 'e' 或 'E' 后跟一个或更多数字.

The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero). Valid numeric data is an optional sign, followed by one or more digits (optionally containing a decimal point), followed by an optional exponent. The exponent is an 'e' or 'E' followed by one or more digits.

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