程序代码：

#include <stdio.h>

#pragma pack(1)

struct file_data
{
    unsigned int day:5;
    unsigned int month:4;
    unsigned int year:7;
};
union Data
{
    unsigned short data;
    struct file_data fd;
};

#pragma pack()

int main()
{
    union Data Hi;
    unsigned short day = 30;
    unsigned short month = 12;
    unsigned short year = 1;
    Hi.data = day + (month << 5) + (year << 9);
    printf("%d/%d/%d\n", Hi.fd.year, Hi.fd.month, Hi.fd.day);
    return 0;
}