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

typedef struct student{
  char name [20];
  int id;
}student;

/*
  1 if success
 0 if fail
 -1 if filename pb
 -2 empty file
*/

int writeArStd(char * filename, student *s, int size){
  unsigned long ans;
  
  //open the file
  FILE *f = fopen(filename, "wb");
  //test open
  if(!f){
    return -1;
  }
  
  //try to write
  ans = fwrite(s, sizeof (student), size, f);
  //test if write was success
  if (ans != size){
    return 0;
  }
  
  //save the file
  ans = fclose(f);
  //test if close success:
  if (ans != 0){//fclose will return 0 in case of success!
    return 0;
  }
  return 1;
}

student * readArStd(char * filename, int *size){
  //first - we have to return the array of students, so we have to allocate it
  //        inside the heap so we avoid TAB-Victim problem
  
  //second- we do not really know the size of the array to be read(and so) to
  //        be allocated in the heap
  
  //third- when we know the size, we will also return it inside *s
  
  unsigned long ans, r = 0;
  student s, *p = NULL; // I need one local variable to count
  int counter = 0;
  
  //open the file
  FILE *f;
  if(!(f = fopen(filename, "rb"))) return NULL;
  
  while(1){
    if (fread(&s, sizeof s, 1, f) != 1) break;
    counter++;
  }
  //I am here because I tried to read 1 student
  //And did not succeed
  //That is because I reached the end of the file
  // (feof(f)) --> return 1;
  if (counter != 0){
    *size = counter;
    //alocate the array in the heap
    p = (student *) malloc( counter * sizeof(student));
    //rewind f
    rewind(f);//set the file position indicator at the beginning
    //fseek would do
    //read in one shot
    fread(p, sizeof s, counter, f);
  }
  
  //close the file
  ans = fclose(f);
  return p;
  
}

void printStudent(student s){
  printf("student [name = %s, id = %d ]\n", s.name, s.id);
}

void test(){
  char *fname = "students";
  int array_size = 0, i;
  
  student *stds, students [] ={"Ali Berro",97206, "Amir Halabi",98613,
                        "Ali Noureldin",96366, "Nidal Jaafar",95135};
  
  int s = sizeof(students)/sizeof(student);
  //for(i=0 ; i<s ; i++) printStudent(students[i]);
  int ans = writeArStd(fname,students,s);
  if (ans != 1)
    return;
  stds = readArStd(fname, &array_size);
  for(i=0 ; i<array_size ; i++){
    printStudent(stds[i]);
  }
  
}
int main(void){
  test();
  return 0;
}