C语言 如何在C中使用逆
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how to use inverse in C
提问by samprat
[how to use ~ operator ]
[如何使用~运算符]
I have a structure say Alpha. I know the value of element inside Alpha(say a) which can be 0or 1- I want the other element of same structure to take inverse value of Alpha.a. For example:
我有一个结构说Alpha。我知道内部元素的值Alpha（比如a）可以是0或1- 我希望相同结构的另一个元素取 Alpha.a 的反值。例如：
if Alpha.a = 1
then Alpha.b = 0
and vice versa
反之亦然
I have tried:
我试过了：
Alpha.b = ~ (Alpha.a)
But unfortunately it doesnt work - when Alpha.ais 1, Alpha.bgets set to 254
但不幸的是它不工作-当Alpha.a是1，Alpha.b被设置为254
Any ideas?
有任何想法吗？
Thanks and regards,
感谢致敬，
SamPrat
桑普拉特
回答by David Given
In C, trueis represented by 1, and falseby 0. However, in a comparison, any non-false value is treated is true.
在 C 中，true用 1 表示，false用 0表示。但是，在比较中，任何非假值都被处理为真。
The !operator does booleaninversion, so !0 is 1 and !1 is 0.
该!运算符执行布尔反转，因此 !0 为 1，!1 为 0。
The ~operator, however, does bitwiseinversion, where every bit in the value is replaced with its inverse. So ~0 is 0xffffffff (-1). ~1 is 0xfffffffe (-2). (And both -1 and -2 are considered as true, which is probably what's confusing you.)
~但是，该运算符执行按位反转，其中值中的每一位都被替换为其倒数。所以 ~0 是 0xffffffff (-1)。~1 是 0xfffffffe (-2)。（并且 -1 和 -2 都被认为是正确的，这可能会让您感到困惑。）
What you want is !, instead of ~.
你想要的是!, 而不是~.
回答by Prince John Wesley
Use XOR operator:
使用异或运算符：
Alpha.b = Alpha.a ^ 1;
回答by Lindydancer
The ~operator negates each individual bit. For example, assume that Alpha.ais an unsigned char. Then ~1would read, in binary as, ~00000001, and the result would be 11111110 (again, in binary), which is the same as 254 in decimal and 0xFE in hex.
该~运营商否定每个位。例如，假设它Alpha.a是一个unsigned char. 然后~1以二进制形式读取 ~00000001，结果将是 11111110（再次以二进制形式），这与十进制的 254 和十六进制的 0xFE 相同。
As others have suggested, use !Alpha.aor Alpha.a ^ 1.
正如其他人所建议的那样，使用!Alpha.a或Alpha.a ^ 1。
回答by Bruce Ricker
A nice cross-platform cross language solution to this common problem is:
这个常见问题的一个很好的跨平台跨语言解决方案是：
Alpha.b = 1 - Alpha.a;
回答by Thorben
What about a postoperational bitmask?
后操作位掩码怎么样？
using unsigned chars looking for bit0:
使用无符号字符查找 bit0：
b = 0x01u & ( ~a );
or even
甚至
b = a ^ 0x01u;
or for "Boolean-Thinkers" ( be aware TRUE and FALSE may differ from 0/1 ! if you want it "real boolean" you should use TRUE and FALSE if defined.)
或者对于“Boolean-Thinkers”（注意 TRUE 和 FALSE 可能与 0/1 不同！如果你想要它“真正的布尔值”，你应该使用 TRUE 和 FALSE 如果定义。）
b = (1 != a)?(0u):(1u);
Cheers
干杯
回答by Chris Snowden
You can't use ~as this will turn 00000000into 11111111rather than 00000001as I think you're expecting.
你不能使用，~因为这会00000000变成11111111而不是00000001我认为你期望的。
If you have bools you can use:
如果你有布尔值，你可以使用：
Alpha.b = !(Alpha.a)
but if not you may have to use if / else logic:
但如果不是，您可能必须使用 if / else 逻辑：
if (Alpha.a == 0)
{
Alpha.b = 1;
}
else
{
Alpha.b = 0;
}
回答by Seth Robertson
You want to use another operator. Specifically !
您想使用其他运算符。具体来说 ！
Alpha.b = !Alpha.a
Since the values are zero or one, it is much simplier.
由于这些值为零或一，因此要简单得多。
