如何将数据从共享存储器复制到文本文件？

Question

概述：

子过程从命令行中获得数字n，n是学生的数量。学生的数据（名称和标记）在命令窗口中输入。

现在，将在共享内存中复制此数据。父程进程是从共享内存中获取这些数据，然后在文件中复制。这就是我遇到的麻烦。如何将这些数据从共享存储器复制到文件？

struct student {
                char name[20];
                float marks;
               };
               
               
int main(int argc, char* argv[])
{
   key_t key = 10;
   int shmID = shmget(key, 100, 0666 | IPC_CREAT | IPC_EXCL);
   pid_t pid;
   pid=fork();

   if(pid==0) 
    {
     //Child writes data of n number of students
     char* child_at = (char*) shmat (shmID,NULL,0);

     int i,n;
     int a = 0;
     n = atoi(argv[1]);
     struct student stuarr[n];
     printf("Number of students: %d\n",n);


     for (i=0;i<n;++i)
     {
       printf("For student %d\nEnter name: ",i+1);
       scanf("%s",stuarr[i].name);

       printf("Enter marks: ");
       scanf("%f",&stuarr[i].marks);

     }
     printf("\n\tName\tMarks\t\n");

        for(i=0; i<n; i++)
                printf("\t%s\t%.2f\t\n", stuarr[i].name, 
                stuarr[i].marks);



        for (i=0;i<n;i++)
         {
           memcpy(child_at + (a * sizeof(struct student)), &stuarr[i], 
           sizeof(struct student));
           a++;
         }
         int d1 = shmdt(child_at);

}

else if (pid>0)
{
   //Parent creates shared memory, waits. Then writes data of students 
   to file
   char* parent_at = shmat(shmID, NULL, 0);
   wait(NULL);
   int i, n = atoi(argv[1]);
   struct student stuarr[n];
   FILE *fptr;
   fptr=(fopen("student.txt","w"));

   if(fptr==NULL)
   {
     printf("Error!");
     exit(1);
   }

   for (i=0;i<n;i++) 
   {

      //HOW TO COPY DATA FROM SHARED MEMORY TO FILE? 

      //memcpy(&stuarr[i].name, &parent_at[i], n);
      //memcpy(&stuarr[i].marks, &parent_at[i], n);

      fprintf(fptr,"\nName: %s", stuarr[i].name, stuarr[i].marks);
   }

   fclose(fptr); 
   int d2 =shmdt(parent_at);
   shmctl(shmID, IPC_RMID, NULL);

}
}