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


struct yonghu {                                                     /*个人注册信息*/  
char name[8];
char sex[4];
char cla[20];
 }stud, student[100];
 void save()
 { FILE *ip;   
if((ip = fopen("student3.txt","a+")) == NULL)
{   printf("不能打开这个文件\n");   return;  
}  
if(fwrite(&stud,sizeof(struct yonghu),1,ip) != 1)  

 printf("信息写入错误!"); fprintf(ip,"\n"); fclose(ip);     
 }  
 void du()
{
 FILE *fp; int i=0,w;
if((fp = fopen("student3.txt","r+")) == NULL)
{   printf("不能打开这个文件\n");   return;
 }
  while(!fp) {
  fread(&student[i],sizeof(struct yonghu),1,fp); i++; }
 }
 for (d = 0; d <= 14; d++)
 {  printf("%s\t%s\t%s",student[d].name[8], student[d].sex[4], student[d].cla[20]);
printf("\n");
 }   
}  
int main()
{  
int d;
 scanf("%s%s%s", stud.name, stud.sex, stud.cla);  
 save();   
du();  
}

if(fwrite(&stud,sizeof(struct yonghu),1,ip) != 1)

你判断这个返回值对吗？？是1还是sizeof(strcut yonghu)？

顶下....



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


struct yonghu {                                                     /*个人注册信息*/  
    char name[8];
    char sex[4];
    char cla[20];
}stud, student[100];
void save()
{
    FILE *ip;   
    if((ip = fopen("student3.txt","a+")) == NULL)
    {
        printf("不能打开这个文件\n");   return;  
    }  
    if(fwrite(&stud,sizeof(struct yonghu),1,ip) != 1)  
        
        printf("信息写入错误!"); fprintf(ip,"\n"); fclose(ip);     
}  
void du()
{
    FILE *fp;
    int i=0,w,d;
    if((fp = fopen("student3.txt","r+")) == NULL)
    {
        printf("不能打开这个文件\n");   return;
    }
    while(!fp)
    {
        fread(&student[i],sizeof(struct yonghu),1,fp); i++;
    }
   
    for (d = 0; d <= 14; d++)
    {
        printf("%s\t%s\t%s",student[d].name[8], student[d].sex[4], student[d].cla[20]);
        printf("\n");
    }   
}  
int main()
{  
    int d;
    scanf("%s%s%s", stud.name, stud.sex, stud.cla);  
    save();   
    du();  
    return 0;
}



/*说句实话，格式太差，

            我给小改了下...
--------------------Configuration: aln - Win32 Debug--------------------
Compiling...
Skipping... (no relevant changes detected)
aln.cpp

aln.obj - 0 error(s), 0 warning(s)
*/

它的这个if的返回值应该是根据最后一个ip为基准的

程序我调试好了没错误了那到你的上面运行下测试结果
我这边没有你的测试数据

#include <stdio.h>
#include <string.h>
#include <conio.h> 
struct yonghu {                                                     /*个人注册信息*/ 
    char name[8];
    char sex[4];
    char cla[20];
}stud, student[100];

void save()
{
    FILE *ip;  
    if((ip = fopen("student3.txt","a+")) == NULL)
    {  
        printf("不能打开这个文件\n");   return; 
    } 
    if(fwrite(&stud,sizeof(struct yonghu),1,ip) != 1) 
       
        printf("信息写入错误!"); fprintf(ip,"\n"); fclose(ip);    
} 

void du()
{
    FILE *fp;
    int i;
    //int w;
    int d;
    i=0;
   
    if((fp = fopen("student3.txt","r+")) == NULL)
    {   printf("不能打开这个文件\n");   return;
    }
    while(!fp)
    {
        fread(&student[i],sizeof(struct yonghu),1,fp); i++;
       
    } 
    for(d=0;d<=14; d++)
    { 
        printf("%s\t%s\t%s",student[d].name[8], student[d].sex[4], student[d].cla[20]);
        printf("\n");
    }  
}

int main()
{ 
    //int d;
    scanf("%s%s%s", stud.name, stud.sex, stud.cla); 
    save();  
    du(); 
} 

我运行了下，
程序还是有问题。

#include <stdio.h>
#include <string.h>
#include <conio.h>
struct yonghu {                                                     /*个人注册信息*/
    char name[8];
    char sex[4];
    char cla[20];
}stud, student[100];

void save()
{
    FILE *ip; 
    if((ip = fopen("C://student3.txt","a+")) == NULL)
    { 
        printf("不能打开这个文件\n");   return;
    }
    if(fwrite(&stud,sizeof(yonghu),1,ip) != 1)
      
        printf("信息写入错误!"); fprintf(ip,"\n"); fclose(ip);   
} 

void du()
{
    FILE *fp=NULL;
    int i;
    //int w;
    int d;
    i=0;
  
    if((fp = fopen("C://student3.txt","r+")) == NULL)
    {   printf("不能打开这个文件\n");   return;
    }
    while(fread(&student[i],sizeof(yonghu),1,fp))
    {
        i++;
    }
    for(d=0;d<=14; d++)
    {
        printf("%s\t%s\t%s",student[d].name, student[d].sex, student[d].cla);
        printf("\n");
    } 
}

int main()
{
    //int d;
//     scanf("%s%s%s", stud.name, stud.sex, stud.cla);
//     save(); 
    du();
} 

可以读出来了  格式自己去控制