PHP将两个不同的字符串表示为相同 [英] PHP expresses two different strings to be the same

问题描述

可能重复:
php == vs ===运算符
如何进行平等(==双重平等)和标识(===三等号)比较运算符是否不同?

Possible Duplicate:
php == vs === operator
How do the equality (== double equals) and identity (=== triple equals) comparison operators differ?

为什么以下语句返回true?

"608E-4234" == "272E-3063"

我也尝试过在字符串周围用单引号引起来.我可以将其评估为false的唯一方法是使用===运算符而不是==

I have also tried this with single quotes around the strings. The only way I can get it to evaulate to false is by using the === operator instead of ==

我的猜测是PHP将其视为一种方程式，但似乎有些奇怪.

My guess is PHP is treating it as some sort of equation but it seems a bit of a strange one.

有人可以详细说明吗?

推荐答案

"608E-4234"是浮点数格式，因此它们在进行比较时会转换为数字.

"608E-4234" is the float number format, so they will cast into number when they compares.

608E-4234和272E-3063都将是float(0)，因为它们太小了.

608E-4234 and 272E-3063 will both be float(0) because they are too small.

对于php中的==，

如果您将数字与字符串进行比较，或者比较涉及 数字字符串，然后将每个字符串转换为数字，然后将 数字比较.

If you compare a number with a string or the comparison involves numerical strings, then each string is converted to a number and the comparison performed numerically.

http://php.net/manual/en/language.operators.comparison.php

注意:

Attention:

那同时具有==和===的javascript中的行为呢?

What about the behavior in javascript which also has both == and ===?

答案是行为不同于PHP.在javascript中，如果您将两个具有相同类型的值进行比较，则==与===相同，因此与两个相同类型的值进行比较不会发生类型转换.

The answer is the behavior is different from PHP. In javascript, if you compare two value with same type, == is just same as ===, so type cast won't happen for compare with two same type values.

在javascript中:

In javascript:

608E-4234 == 272E-3063 // true
608E-4234 == "272E-3063" // true
"608E-4234" == 272E-3063 // true
"608E-4234" == "272E-3063" // false (Note: this is different form PHP)

因此在javascript中，当您知道结果的类型时，可以使用==而不是===来保存一个字符.

So in javascript, when you know the type of the result, you could use == instead of === to save one character.

例如，typeof运算符总是返回一个字符串，因此您可以只使用

For example, typeof operator always returns a string, so you could just use

typeof foo == 'string'而不是typeof foo === 'string'无害.

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