php ~ 按位运算符 (波浪号) 的功能是什么
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What's the function of the ~ bitwise operator (Tilde)
提问by Michiel
Possible Duplicate:
What does this ~ operator mean here?
Bit not operation in PHP(or any other language probably)
Can someone explain me the ~operator in PHP? I know it's a NOT-operator, but why does PHP convert following statement to the negative value of the variable minus one?
有人可以向我解释~PHP 中的运算符吗？我知道它是一个NOT-operator，但为什么 PHP 将以下语句转换为变量的负值减去一？
$a = 1; echo ~$a // echo -2
$a = 2; echo ~$a // echo -3
$a = 3; echo ~$a // echo -4
回答by buc
This is called the two's complement arithmetic. You can read about it in more detail here.
这称为二进制补码算法。您可以在此处详细了解它。
The operator ~is a binary negation operator (as opposed to boolean negation), and being that, it inverses all the bits of its operand. The result is a negative number in two's complement arithmetic.
该运算符~是一个二元否定运算符（与布尔否定相反），因此，它反转其操作数的所有位。结果是二进制补码运算中的负数。
回答by akond
It's a bitwise NOT.
这是一个位不。
It converts all 1s to 0s, and all 0s to 1s. So 1 becomes -2 (0b111111111110 in binary representation).
它将所有的 1 转换为 0，将所有的 0 转换为 1。所以 1 变成 -2（二进制表示为 0b111111111110）。
Have a look at the doc http://php.net/manual/en/language.operators.bitwise.php
看看文档 http://php.net/manual/en/language.operators.bitwise.php
回答by cHao
~flips all the bits of the number. In two's complement (google it), mathematical negation is achievable by flipping all the bits and then adding 1. If you only do the first step (ie: just flip the bits), you have the additive inverse minus 1.
~翻转数字的所有位。在二进制补码（google it）中，可以通过翻转所有位然后加 1 来实现数学否定。如果您只执行第一步（即：仅翻转位），则加法逆减 1。
