#include<stdio.h>
#include<stdlib.h>
#define N 4
struct student
{
    unsigned num;
    char     name[9];
    unsigned cla;
    int      score;
   
};

//写数据的函数
void  stu_write()
{
    int i;
    struct student stu;
    FILE * fp;
    if((fp=fopen("student.txt","w"))==NULL)
    {
        printf("打开文件失败");
        exit(1);
    }

    for(i=0;i!=N;i++)
    {
        scanf("%d %s %d %d",&stu.num,stu.name,&stu.cla,&stu.score);
        fprintf(fp,"%2d%-8s%1d%3d\n",stu.num,stu.name,stu.cla,stu.score);
    }
    fclose(fp);
}
//读数据并排序的函数
void stu_read_sort()
{
    int i,j,k;
    struct student stu[N],t;
    FILE *fp;
    if((fp=fopen("student.txt","r"))==NULL)
    {
        printf("打开文件失败");
        exit(1);
    }
    else
        printf("打开成功");
    //读数据
    i=0;
    fscanf(fp,"%2d %-8s %1d %3d\n",&stu[i].num,stu[i].name,&stu[i].cla,&stu[i].score);
    while(!feof(fp));
    {      
        i++;
        fseek(fp,(2+8+1+3+2*3+2)*i,0);
        fscanf(fp,"%2d，%-8s，%1d，%3d\n",&stu[i].num,stu[i].name,&stu[i].cla,&stu[i].score);
   
    }
    fclose(fp);//打开文件再关上文件，以防文件数据丢失
    printf("从文件写入内存结构体数组成功！！！");


    //排序
    for(i=0;i<=N-2;i++)
    {
        k=i;
        for(j=i+1;j<=N-1;j++)
            if(stu[k].score<stu[j].score)
                k=j;
            t=stu[k];
            stu[k]=stu[i];
            stu[i]=t;
    }
    //输出
    for(i=0;i<=N-1;i++)
    printf("%2d %-8s %1d %3d\n",stu[i].num,stu[i].name,stu[i].cla,stu[i].score);
}

//测试函数

int main()
{   
    stu_write();
    stu_read_sort();
    return 0;
}

fseek(fp,(2+8+1+3+2*3+2)*i,0);  
这个地方很重要，如果偏移的位置不恰到好处，就会程序报错