我的结构体为什么只写进去了123456？

Question

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

typedef struct book{
    char name[16];
    char id[8];        //存八位编号
    int loaned;        //借出
    int num;        //总数
    double price;
    char publisher[32];
    char author[32];
    struct book*next;
}book;

typedef struct student{
    char id[8];
    char name[16];
    int overdue;        //逾期数
    char borrow_book_name[5][32];    //借书数，最大为5,用编号存
    int borrow_book_num;
    struct student*next;
}student;

void Print(book*Head);
int main(){
    student sd = {"123456","hy",0,{"asd"},1,NULL};
    FILE*fp = fopen("student.dat","w");
    fwrite(&sd,sizeof(student),1,fp);
    fclose(fp);
    return 0;
}

Answer 1

都写进去了的。
注意一下空白字符也被写进去了，比如char name[16]这个，他就会占用16个字节，所以看起来会有很多空白