联合体嵌套结构体

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

typedef unsigned char UINT8;

struct entity { char char0; char char1; char char2; char char3; unsigned short char4;};
union name{ char _name[6]; struct entity Fname;};

struct FLAG {
    UINT8 bit0 : 1;
    UINT8 bit1 : 1;
    UINT8 bit2 : 1;
    UINT8 bit3 : 1;
    UINT8 bit4 : 1;
    UINT8 bit5 : 1;
    UINT8 bit6 : 1;
    UINT8 bit7 : 1;
};
// 联合体里面套用结构体
union FLAGS { UINT8 byte; struct FLAG bit;};

union name myname;

volatile union FLAGS net_flag;
#define DEV_DIS         net_flag.bit.bit0
#define ON      1

void main() {
    char *test = "abcdA";
    char _test[] = "abcdA";
    char __test[6] = "abcdA";
    // 分别输出串长度、指针地址size、[]声明字符串会自动加\0结束符，即长度自动加1
    printf("test strlen :%d sizeof(test) :%d sizeof(_test) :%d\n",strlen(test),sizeof(test), sizeof(_test));
    // [6]声明字符串strlen取决于长度，sizeof取决于[]分配的大小，如使用memset的时候注意两个函数的区别
    printf("__test strlen :%d sizeof(test) :%d\n", strlen(__test), sizeof(__test));
    strcpy_s(myname._name,sizeof(test), test);
    printf("sizeof char, unsigned short, int :%d, %d, %d\n", sizeof(char),sizeof(unsigned short),sizeof(int));
    printf("myname size :%d\n",sizeof(myname));
    printf("myname._name size :%d\n", sizeof(myname._name));
    printf("myname.Fname size :%d\n", sizeof(myname.Fname));
    printf("myname.Fname include :%c %c %c %c %c\n", myname.Fname.char0, myname.Fname.char1, myname.Fname.char2, myname.Fname.char3, myname.Fname.char4);

    /* 联合体的特性 */
    union FLAGS flags;
    flags.byte = 8;

    printf(" flags 's size :%d value :%d \n",sizeof(flags.bit),flags.bit.bit2);

    flags.bit.bit0 = 0;
    flags.bit.bit1 = 0;
    flags.bit.bit2 = 1;
    flags.bit.bit3 = 1;
    printf(" flags 's size :%d value :%d", sizeof(flags.bit), flags.byte);
}