按位索引用C？ [英] bitwise indexing in C?

问题描述

我想实现数据的COM pression想法我已经过了，因为我想象它运行对一个大语料库的测试数据，我原以为到code在C（我主要是在脚本语言如Ruby和Tcl经验。）

I'm trying to implement a data compression idea I've had, and since I'm imagining running it against a large corpus of test data, I had thought to code it in C (I mostly have experience in scripting languages like Ruby and Tcl.)

看，我意识到，我不能简单地以指数作为我希望做按位比较简单的字符或INT类型变量的位，运营商。

Looking through the O'Reilly 'cow' books on C, I realize that I can't simply index the bits of a simple 'char' or 'int' type variable as I'd like to to do bitwise comparisons and operators.

我在这种看法正确吗？它是合理的，我用枚举类型重新presenting位（和使这些阵列，和写入功能转换和从CHAR）？如果是这样，就是这样一个类型和函数标准库定义已经地方？是否有其他（更好？）接近？有一些例如code的地方，有人可以点我？

Am I correct in this perception? Is it reasonable for me to use an enumerated type for representing a bit (and make an array of these, and writing functions to convert to and from char)? If so, is such a type and functions defined in a standard library already somewhere? Are there other (better?) approaches? Is there some example code somewhere that someone could point me to?

谢谢 -

推荐答案

这是什么凯尔说继，您可以使用宏来完成复杂的工作适合你。

Following on from what Kyle has said, you can use a macro to do the hard work for you.

这是可能的。

要设置的第n个位，使用或：

To set the nth bit, use OR:

X | =（1 <<;小于5）; //设置5日，从
  权

x |= (1 << 5); // sets the 5th-from right

要清除位，使用和：

X - 放大器; =〜（1 <<;小于5）; //清零
  第五，从右

x &= ~(1 << 5); // clears 5th-from-right

要翻转了一下，使用XOR：

To flip a bit, use XOR:

的x ^ =（1 <<;小于5）; //翻转5 - 从右

x ^= (1 << 5); // flips 5th-from-right

或...

#define GetBit(var, bit) ((var & (1 << bit)) != 0) // Returns true / false if bit is set
#define SetBit(var, bit) (var |= (1 << bit))
#define FlipBit(var, bit) (var ^= (1 << bit))

然后你可以使用它在code，如：

Then you can use it in code like:

int myVar = 0;
SetBit(myVar, 5);
if (GetBit(myVar, 5))
{
  // Do something
}

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