Read/write binary files array of structs

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i have global struct array book_array with some values in it..and another global array a uninitialized .. simply I want to copy book_array content to a binary file and read this file into array a.. my program doesn't seem to work and array a doesn't print anything!! any help plz

What I have tried:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{

    int day;
    int month;
    int year;
} dateStruct;

typedef struct
{
    char title[100];
    char author[100];
    char publisher[100];
    char ISBN[30];
    dateStruct date;
    int copies;
    int current;
    char category[30];
} book;
book book_array[100] ;
int i=4;
book a[4];
void library_books(){

    strcpy( book_array[0].title,"Automation and Robotics");
    strcpy( book_array[0].author,"Miltiadis Boboulos");
    strcpy( book_array[0].ISBN,"978-87-7681");
    strcpy(book_array[0].category,"Electrical engineering");
    book_array[0].copies=10;
    book_array[0].current=8;
    book_array[0].date.day=22;
    book_array[0].date.month=12;
    book_array[0].date.year=2017;
    strcpy( book_array[0].publisher,"book boon");

    strcpy( book_array[1].title,"Concepts in Electric Circuits");
    strcpy( book_array[1].author," Wasif Naem");
    strcpy(  book_array[1].ISBN,"7681-499-1");
    strcpy(book_array[1].category,"Electrical engineering");
    book_array[1].copies=20;
    book_array[1].current=10;
    book_array[1].date.day=21;
    book_array[1].date.month=12;
    book_array[1].date.year=2017;
    strcpy( book_array[1].publisher,"book boon");

    strcpy( book_array[2].title,"Engineering Thermodynamics");
    strcpy( book_array[2].author,"Tarik Shemmeri");
    strcpy( book_array[2].ISBN,"7681-670-4");
    strcpy(book_array[2].category,"Mechanical engineering");
    book_array[2].copies=7;
    book_array[2].current=5;
    book_array[2].date.day=20;
    book_array[2].date.month=12;
    book_array[2].date.year=2017;
    strcpy( book_array[2].publisher,"book boon");

    strcpy( book_array[3].title,"Fundamentals of Construction Management");
    strcpy( book_array[3].author,"Dr. Abimbola Windapo");
    strcpy( book_array[3].ISBN,"403-0362-9");
    strcpy(book_array[3].category,"construction engineering");
    book_array[3].copies=12;
    book_array[3].current=11;
    book_array[3].date.day=19;
    book_array[3].date.month=11;
    book_array[3].date.year=2017;
    strcpy( book_array[3].publisher,"Acair Ltd");

}
void write_book(char fileName[]){
int j=0;
FILE* ptr= fopen(fileName,"wb");
if(ptr==NULL) exit(1);
while(!feof(ptr)&&j<i){
    fwrite(book_array,sizeof(book_array),1,ptr);
    }
fclose(ptr);
}
void read_book(char fileName[]){
int j=0;
FILE* fptr= fopen(fileName,"rb");
if(fptr==NULL) exit(1);
while(!feof(fptr))
    fread(&(a),sizeof(a),3,fptr);
fclose(fptr);
}
int main()
{
   library_books();
   write_book("b.dat");
   read_book("b.dat");
   printf("%s\n",a[0].author);
   printf("%s\n",a[1].ISBN);
   printf("%d\n",a[2].date.day);
    return 0;
}

Posted 21-Dec-17 20:44pm

Member 13476370

Updated 21-Dec-17 21:45pm

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CPallini · Answer 1 · 2017-12-21T21:45:00

Don't use globals. Parametrize your functions, instead. Try

C

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

typedef struct
{
  int day;
  int month;
  int year;
} dateStruct;

typedef struct
{
  char title[100];
  char author[100];
  char publisher[100];
  char ISBN[30];
  dateStruct date;
  int copies;
  int current;
  char category[30];
} book;

int library_books(book book_array[])
{
  strcpy( book_array[0].title,"Automation and Robotics");
  strcpy( book_array[0].author,"Miltiadis Boboulos");
  strcpy( book_array[0].ISBN,"978-87-7681");
  strcpy(book_array[0].category,"Electrical engineering");
  book_array[0].copies=10;
  book_array[0].current=8;
  book_array[0].date.day=22;
  book_array[0].date.month=12;
  book_array[0].date.year=2017;
  strcpy( book_array[0].publisher,"book boon");

  strcpy( book_array[1].title,"Concepts in Electric Circuits");
  strcpy( book_array[1].author," Wasif Naem");
  strcpy(  book_array[1].ISBN,"7681-499-1");
  strcpy(book_array[1].category,"Electrical engineering");
  book_array[1].copies=20;
  book_array[1].current=10;
  book_array[1].date.day=21;
  book_array[1].date.month=12;
  book_array[1].date.year=2017;
  strcpy( book_array[1].publisher,"book boon");

  strcpy( book_array[2].title,"Engineering Thermodynamics");
  strcpy( book_array[2].author,"Tarik Shemmeri");
  strcpy( book_array[2].ISBN,"7681-670-4");
  strcpy(book_array[2].category,"Mechanical engineering");
  book_array[2].copies=7;
  book_array[2].current=5;
  book_array[2].date.day=20;
  book_array[2].date.month=12;
  book_array[2].date.year=2017;
  strcpy( book_array[2].publisher,"book boon");
  strcpy( book_array[3].title,"Fundamentals of Construction Management");
  strcpy( book_array[3].author,"Dr. Abimbola Windapo");
  strcpy( book_array[3].ISBN,"403-0362-9");
  strcpy(book_array[3].category,"construction engineering");
  book_array[3].copies=12;
  book_array[3].current=11;
  book_array[3].date.day=19;
  book_array[3].date.month=11;
  book_array[3].date.year=2017;
  strcpy( book_array[3].publisher,"Acair Ltd");

  return 4; // return the no. of filled items
}

void write_books(book a[], int items, const char * fileName)
{
  FILE* ptr = fopen(fileName,"wb");
  if(! ptr) return; // TODO: better error handling
  fwrite( a, sizeof(book), items, ptr);
  fclose(ptr);
}
int read_books(book a[], const char * fileName)
{
  FILE* ptr = fopen(fileName,"rb");
  if( !ptr ) return 0;
  int n = 0;
  for (n=0; !feof(ptr); ++n)
  {
    if ( fread(&a[n],sizeof(book),1,ptr) != 1) break;
  }

  fclose(ptr);
  return n;
}
int main()
{
  book book_array[100] ;

  int items;

  items = library_books(book_array);

  if (items < 1) return -1;

  write_books( book_array, items, "b.dat");

  book * a = malloc(sizeof(book) * items);
  if ( ! a) return 0;

  items = read_books( a, "b.dat");

  printf("read %d books\n",  items);

  printf("%s\n",a[0].author);
  printf("%s\n",a[1].ISBN);
  printf("%d\n",a[2].date.day);

  free (a);

  return 0;
}