[C++知识库]c语言bitField

#include <cstdio>

void printf_bin2(void *dataPtr, int sizeOfData) {
    int i, j;
    unsigned char *p = (unsigned char *) dataPtr + (sizeOfData - 1);//p先指向num后面第3个字节的地址，即num的最高位字节地址

    for (i = 0; i < sizeOfData; i++) //依次处理4个字节(32位）
    {
        j = *(p - i); //取每个字节的首地址，从高位字节到低位字节，即p p-1 p-2 p-3地址处
        for (int k = 7; k >= 0; k--) //处理每个字节的8个位，注意字节内部的二进制数是按照人的习惯存储！
        {
            if (j & (1 << k))//1左移k位，与单前的字节内容j进行或运算，如k=7时，00000000&10000000=0 ->该字节的最高位为0
                printf("1");
            else
                printf("0");
        }
        printf(" ");//每8位加个空格，方便查看
    }
    printf("\r\n");
}


// A structure without forced alignment
struct Test1 {
    unsigned int x: 5;
    unsigned int y: 8;
};

// A structure with forced alignment
struct Test2 {
    unsigned int x: 5;
    unsigned int : 0;
    unsigned int y: 8;
};

int main() {
    printf("Size of test1 is %lu bytes\n",
           sizeof(struct Test1));
    Test1 test1{0};
    test1.x = 1;
    test1.y = 2;
    printf_bin2(&test1, sizeof(Test1));

    printf("Size of test2 is %lu bytes\n",
           sizeof(struct Test2));

    Test2 test2{0};
    test2.x = 1;
    test2.y = 2;
    printf_bin2(&test2, sizeof(Test2));
    return 0;
}

Size of test1 is 4 bytes
00000000 00000000 00000000 01000001 
Size of test2 is 8 bytes
00000000 00000000 00000000 00000010 00000000 00000000 00000000 00000001 

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