该怎么改？
#include <stdio.h>
#include <malloc.h>
#include <string.h>
typedef struct student{
     int cla;
     int num;
     char name[20];
     char sex;
     long phone;
}student;
typedef struct {
     student *elem;
     int length;
}SSTable;
void createlist(SSTable ST){
    int i,n;
    printf("请输入学生的个数：\n");
    scanf("%d",&n);
    printf("请输入%d个学生信息(class/name/num/sex/phone):\n",n);
    for(i=0;i<n;i++){
        scanf("%d %s %d %c %ld",&ST.elem[i].cla,&ST.elem[i].name,
            &ST.elem[i].num,&ST.elem[i].sex,&ST.elem[i].phone);
    }
}
void searchbin(SSTable ST) {
    int low=1,high=ST.length,mid,num,c;
    printf("输入查找人的学号和班级号:");
    scanf("%d %d",&num,&c);
    while(low<=high){
            mid=(low+high)/2;
            if(ST.elem[mid].num<num) low=mid+1;
            else if(ST.elem[mid].num>num) high=mid-1;
            else{
                if(ST.elem[mid].cla<c)mid++;
                else if(ST.elem[mid].cla>c)mid--;
                break;
            }
    printf("class:%d,name:%s,num:%d,sex:%c,phone:%ld\n",ST.elem[mid].cla,
        ST.elem[mid].name,ST.elem[mid].num,ST.elem[mid].sex,ST.elem[mid].phone);
    }
}
void main(){
    SSTable ST;
    createlist(ST);
    searchbin(ST);
}

ST.elem 没有指向，编译时有没有提醒你ST没有初始化

student *elem;    //假设占四个字节

四个字节肯定放不下这么多东西
for(i=0;i<n;i++){
        scanf("%d %s %d %c %ld",&ST.elem[i].cla,&ST.elem[i].name,
            &ST.elem[i].num,&ST.elem[i].sex,&ST.elem[i].phone);
    }

ST没有初始化编译可以通过？？    好吧   vs不能反正