在无符号32位整数中查找位位置

有几点:首先,任何真正习惯C的人通常会从0开始编号,而不是1。其次,你可以用按位and运算符测试各个标志( &

#define flag1 1    //  1 = 00 0001
#define flag2 2    //  2 = 00 0010
#define flag3 4    //  4 = 00 0100
#define flag4 8    //  8 = 00 1000
#define flag5 16   // 16 = 01 0000
#define flag6 32   // 32 = 10 0000

if (myvalue & flag1)
    // flag1 was set

if (myvalue & flag4)
    // flag4 was set

等等。您还可以检查循环中设置了哪些位:

#include <stdio.h>

int main() { 
    int myvalue = 28;
    int i, iter;

    for (i=1, iter=1; i<256; i<<=1, iter++)
        if (myvalue & i)
            printf("Flag: %d set\n", iter);
    return 0;
}

Flag: 3 set
Flag: 4 set
Flag: 5 set

您可以只循环设置的位,而不是循环每一个位,如果您希望位的设置稀疏,则循环速度会更快:

while (field){
  temp = field & -field;  //extract least significant bit on a 2s complement machine
  field ^= temp;  // toggle the bit off
  //now you could have a switch statement or bunch of conditionals to test temp
  //or get the index of the bit and index into a jump table, etc.
}

得到一个 int 0 1 只代表 n

int bitN = (value >> n) & 1;

但这通常不是你想做的。一个更常见的成语是:

int bitN = value & (1 << n);

在这种情况下 bitN 将 0 如果 n n 位已设置(具体来说,它将是任何价值出来的只是 n 第位设置。)

flags 未签名。。。

int flag_num = 1;
while (flags != 0)
{
    if ((flags&1) != 0)
    {
        printf("Flag %d set\n", flags);
    }
    flags >>= 1;
    flag_num += 1;
}

你应该替换

flags >>= 1;

flags = (flags >> 1) & 0x7fffffff;

在python中,使用一个以2为基数的log函数,如下所示:

import math 

position = math.log(value, 2)

@invaliddata的答案略有变化-

unsigned int tmp_bitmap = x;        
while (tmp_bitmap > 0) {
    int next_psn = __builtin_ffs(tmp_bitmap) - 1;
    tmp_bitmap &= (tmp_bitmap-1);
    printf("Flag: %d set\n", next_psn);
}

// You can check the bit set positions of 32 bit integer.
// That's why the check is added "i != 0 && i <= val" to iterate till 
// the end bit position.
    void find_bit_pos(unsigned int val) {
            unsigned int i;
            int bit_pos;
            printf("%u::\n", val);
            for(i = 1, bit_pos = 1; i != 0 && i <= val; i <<= 1, bit_pos++) { 
                    if(val & i)
                            printf("set bit pos: %d\n", bit_pos);
            }
    }