对于初学者，我想用一个例子解释一下：

例子：

value is 0x55;
bitnum : 3rd.

使用&运算符检查位：

0101 0101
&
0000 1000
___________
0000 0000 (mean 0: False). It will work fine if the third bit is 1 (then the answer will be True)

切换或翻转：

0101 0101
^
0000 1000
___________
0101 1101 (Flip the third bit without affecting other bits)

|运算符：设置位

0101 0101
|
0000 1000
___________
0101 1101 (set the third bit without affecting other bits)

int set_nth_bit(int num, int n){    
    return (num | 1 << n);
}

int clear_nth_bit(int num, int n){    
    return (num & ~( 1 << n));
}

int toggle_nth_bit(int num, int n){    
    return num ^ (1 << n);
}

int check_nth_bit(int num, int n){    
    return num & (1 << n);
}

尝试使用C语言中的以下函数之一更改n位：

char bitfield;

// Start at 0th position

void chang_n_bit(int n, int value)
{
    bitfield = (bitfield | (1 << n)) & (~( (1 << n) ^ (value << n) ));
}

Or

void chang_n_bit(int n, int value)
{
    bitfield = (bitfield | (1 << n)) & ((value << n) | ((~0) ^ (1 << n)));
}

Or

void chang_n_bit(int n, int value)
{
    if(value)
        bitfield |= 1 << n;
    else
        bitfield &= ~0 ^ (1 << n);
}

char get_n_bit(int n)
{
    return (bitfield & (1 << n)) ? 1 : 0;
}

使用标准C++库：std:：bitset＜N＞。

或者Boost版本：Boost:：dynamic_bitset。

没有必要自己动手：

#include <bitset>
#include <iostream>

int main()
{
    std::bitset<5> x;

    x[1] = 1;
    x[2] = 0;
    // Note x[0-4]  valid

    std::cout << x << std::endl;
}

[Alpha:] > ./a.out
00010

与标准库编译时大小的位集相比，Boost版本允许运行时大小的比特集。

如果您想在Linux内核中使用C编程执行所有操作，那么我建议使用Linux内核的标准API。

看见https://www.kernel.org/doc/htmldocs/kernel-api/ch02s03.html

set_bit  Atomically set a bit in memory
clear_bit  Clears a bit in memory
change_bit  Toggle a bit in memory
test_and_set_bit  Set a bit and return its old value
test_and_clear_bit  Clear a bit and return its old value
test_and_change_bit  Change a bit and return its old value
test_bit  Determine whether a bit is set

注意：这里整个操作在一个步骤中完成。因此，即使在SMP计算机上，这些都保证是原子的，并且是有用的以保持处理器之间的一致性。

模板版本（放在头文件中），支持更改多位（适用于AVR微控制器btw）：

namespace bit {
  template <typename T1, typename T2>
  constexpr inline T1 bitmask(T2 bit) 
  {return (T1)1 << bit;}
  template <typename T1, typename T3, typename ...T2>
  constexpr inline T1 bitmask(T3 bit, T2 ...bits) 
  {return ((T1)1 << bit) | bitmask<T1>(bits...);}

  /** Set these bits (others retain their state) */
  template <typename T1, typename ...T2>
  constexpr inline void set (T1 &variable, T2 ...bits) 
  {variable |= bitmask<T1>(bits...);}
  /** Set only these bits (others will be cleared) */
  template <typename T1, typename ...T2>
  constexpr inline void setOnly (T1 &variable, T2 ...bits) 
  {variable = bitmask<T1>(bits...);}
  /** Clear these bits (others retain their state) */
  template <typename T1, typename ...T2>
  constexpr inline void clear (T1 &variable, T2 ...bits) 
  {variable &= ~bitmask<T1>(bits...);}
  /** Flip these bits (others retain their state) */
  template <typename T1, typename ...T2>
  constexpr inline void flip (T1 &variable, T2 ...bits) 
  {variable ^= bitmask<T1>(bits...);}
  /** Check if any of these bits are set */
  template <typename T1, typename ...T2>
  constexpr inline bool isAnySet(const T1 &variable, T2 ...bits) 
  {return variable & bitmask<T1>(bits...);}
  /** Check if all these bits are set */
  template <typename T1, typename ...T2>
  constexpr inline bool isSet (const T1 &variable, T2 ...bits) 
  {return ((variable & bitmask<T1>(bits...)) == bitmask<T1>(bits...));}
  /** Check if all these bits are not set */
  template <typename T1, typename ...T2>
  constexpr inline bool isNotSet (const T1 &variable, T2 ...bits) 
  {return ((variable & bitmask<T1>(bits...)) != bitmask<T1>(bits...));}
}

使用示例：

#include <iostream>
#include <bitset> // for console output of binary values

// and include the code above of course

using namespace std;

int main() {
  uint8_t v = 0b1111'1100;
  bit::set(v, 0);
  cout << bitset<8>(v) << endl;

  bit::clear(v, 0,1);
  cout << bitset<8>(v) << endl;

  bit::flip(v, 0,1);
  cout << bitset<8>(v) << endl;

  bit::clear(v, 0,1,2,3,4,5,6,7);
  cout << bitset<8>(v) << endl;

  bit::flip(v, 0,7);
  cout << bitset<8>(v) << endl;
}

BTW：如果不向编译器发送优化器参数（例如：-O3），则不使用constexpr和inline。请随时尝试以下代码https://godbolt.org/并查看ASM输出。