在C linux中的一个字符数组中存储一个位[关闭]答案

【问题标题】：storing a bit in a bit of character array in C linux [closed]在C linux中的一个字符数组中存储一个位[关闭]
【发布时间】：2014-05-08 08:52:20
【问题描述】：

我怎样才能一点一点地存储一点？我需要提取各种号码。来自不同变量的位并将它们放入缓冲区中，如图所示。

unsigned char a;
a=5;

现在我想获取 LSB 并将其存储在 unsigned char 类型的缓冲区中。

unsigned char buffer[5];

为了提取我正在使用

a & 00000001

现在如何存储它以及之后的更多位？

【问题讨论】：

除非我错过了一些更深层次的错误或隐藏的含义：buffer[0] = a & 1 ..?? （另外，在 C 语言中输入以 0 开头的数字时，最好小心！）
buffer[0] 是一个字节，而不是位...
然后使用buffer[0] = a。看？这样，您可以一次将 a 的所有“位”存储到 buffer[0] 中；您甚至不必一次这样做...请编辑您的问题并添加更多详细信息。您实际上需要做什么？如您所见，“我想存储位”有点宽泛。
C 中除了位域外没有位数据类型。为什么不只存储buffer[0] = a 或buffer[0] = a & 0x01？

标签： c char bit

【解决方案1】：

我不确定你想做什么，但这里是一个按位移位的例子。

unsigned char b;
unsigned char c;

b = a & (1 << 0); /* Will store the least significant bit of a in b*/
c = a & (1 << 1); /* Will store the 2nd least significant bit of a in c*/

您可以使用它来创建只有有限位数的变量。

typedef struct bit_s
{
    unsigned int    a : 1; /* only 1 bit available */
    unsigned int    b : 12; /* only 12 bits available */
}              bit_t;

bit_t var;

var.a = 0;
var.a = 1;
var.a = 2; /* Will overflow the variable and create a warning with -Woverflow */

【讨论】：

【解决方案2】：

使用移位运算符>>

buffer[0] = a & 0x01; // 1 will be stores to buffer[0] if LSB of a is one
buffer[1] = (a >> 1) & 0x01; // 1 will be stored to buffer[1] if 2nd bit of a is one.

【讨论】：

【解决方案3】：

类似：

(apologies for syntax errors etc. this is untested code! ) 


unsigned char getbit;
unsigned char storeBit[5];

for (x = 0; x < inBufferLength ; x++) {
  // get least significant bit
  getbit = inBuffer[x] & x00000001;
  int ByteNum = x / 8;
  int BitNum = x % 8;
  if (getBit) {
    switch (BitNum) {
     case 0;
        storeBit[ByteNum] = storeBit[ByteNum] | x10000000;
        break; 
     case 1;
        storeBit[ByteNum] = storeBit[ByteNum] | x01000000;
        break; 
     case 2;
        storeBit[ByteNum] = storeBit[ByteNum] | x00100000;
        break;
     case 3;
        storeBit[ByteNum] = storeBit[ByteNum] | x00010000;
        break; 
     case 4;
        storeBit[ByteNum] = storeBit[ByteNum] | x00001000;
        break; 
     case 5;
        storeBit[ByteNum] = storeBit[ByteNum] | x00000100;
        break; 
     case 6;
        storeBit[ByteNum] = storeBit[ByteNum] | x00000010;
        break; 
     case 7;
        storeBit[ByteNum] = storeBit[ByteNum] | x00000001;
        break;
     }
  }

【讨论】：

【解决方案4】：

设置位...

/** Set bit in any sized bit block.
 *
 * @return   none
 *
 * @param   bit    - Bit number.
 * @param   bitmap - Pointer to bitmap.
 *
 * @note    Please note that this function does not know the size of the
 *          bitmap and it cannot range check the specified bit number.
 */
void SetBit( int bit, unsigned char *bitmap)
{
    int n, x;

    x = bit / 8;                        // Index to byte.
    n = bit % 8;                        // Specific bit in byte.

    bitmap[x] |= (1 << n);      // Set bit.
}

重置位...

/** Reset bit in any sized mask.
 *
 * @return  None
 *
 * @param   bit    - Bit number.
 * @param   bitmap - Pointer to bitmap.
 *
 * @note    Please note that this function does not know the size of the
 *          bitmap and it cannot range check the specified bit number.
 */
void ResetBit( int bit, unsigned char *bitmap)
{
    int n, x;

    x = bit / 8;                        // Index to byte.
    n = bit % 8;                        // Specific bit in byte.

    bitmap[x] &= (1 << n);              // Reset bit.
}

切换位...

/** Toggle bit in any sized bit mask.
 *
 * @return   none
 *
 * @param   bit    - Bit number.
 * @param   bitmap - Pointer to bitmap.
 *
 * @note    Please note that this function does not know the size of the
 *          bitmap and it cannot range check the specified bit number.
 */
void ToggleBit( int bit, unsigned char *bitmap)
{
    int n, x;

    x = bit / 8;                        // Index to byte.
    n = bit % 8;                        // Specific bit in byte.

    bitmap[x] ^= (1<<n);        // Toggle bit.
}

检查位...

/** Checks specified bit.
 *
 * @return  1 if bit set else 0.
 *
 * @param   bit    - Bit number.
 * @param   bitmap - Pointer to bitmap.
 *
 * @note    Please note that this function does not know the size of the
 *          bitmap and it cannot range check the specified bit number.
 */
int IsBitSet( int bit, const unsigned char *bitmap)
{
    int n, x;

    x = bit / 8;            // Index to byte.
    n = bit % 8;            // Specific bit in byte.

    // Test bit (logigal AND).
    if (bitmap[x] & (1<<n))
        return 1;

    return 0;
}

是位复位...

/** Checks specified bit.
 *
 * @return  1 if bit reset else 0.
 *
 * @param   bit    - Bit number.
 * @param   bitmap - Pointer to bitmap.
 *
 * @note    Please note that this function does not know the size of the
 *          bitmap and it cannot range check the specified bit number.
 */
int IsBitReset( int bit, const unsigned char *bitmap)
{
    return IsBitSet( bit, bitmap) ^ 1;
}

希望这会有所帮助...

Usefull bit twiddling hacks...

【讨论】：