c - 如何在一字节整数中存储2位、1位、1位和四位值

Question

我是存储此类值的新手。我的标题字段值很少。2bit = 2 , 1bit = 1, 1 bit = 0, 4bit = 13。如何按顺序将其存储在 uint8 中？请帮助我。

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

int main(void) {
   uint8_t m;
   uint8_t one, two, three, four;
   one = 2;
   two = 1;
   three = 1;
   four = 13;

   // do not know how to store, 

   //assuming m is stored
   one = (m >> 7) & 1;
   two = (m >> 5) & 3;
   three = (m >> 4) & 1;
   four = m & 15;
   printf("first %i , second %i, third %i, four %i", one, two, three, four);
   return 0
} 

Answer 1

看来您已经知道如何使用位移位来检索存储的值。将其反转以存储值。

m = ((one & 1) << 7) | ((two & 3) << 5) | ((three & 1) << 4) | (four & 15);

此代码基于您的代码:one 是 1 位，two 是 2 位，two 是 1 位， four 是 4 位宽。 2 被分配给 one，因此它会被 & 1 视为零。

如果您想将 2 位分配给 one，将 1 位分配给 two，请使用此存储:

m = ((one & 3) << 6) | ((two & 1) << 5) | ((three & 1) << 4) | (four & 15);

这个用于检索:

one = (m >> 6) & 3;
two = (m >> 5) & 1;
three = (m >> 4) & 1;
four = m & 15;