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Reading from a binary file

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# 1  
Old 04-22-2002
Question Reading from a binary file
I'm having trouble with reading information back into a program from a binary file. when i try to display the contents of the file i get a Memory fault(coredump). would anyone be able to assist?
this is my fread line
Code:
fread(&file_data,sizeof(struct book_type),1,fileSave);

ive also tried it without the & but i still get the coredump.
thanks!
primal

here is some other information that might be required...
global variable
Code:
struct book_type{
    char title[30];
    float price;
    char authorName[30];
    struct book_type * link;
   };

saving to file
Code:
fwrite(book_head,sizeof(struct book_type),1,fileSave);
fwrite(temp,sizeof(struct book_type),1,fileSave);

function definition
Code:
void display_File_Data(){
     char ch;
     int count=1;
     struct book_type * file_data;
     rewind(fileSave);
     printf("\nSerial Number\tTitle\t\tAuthor\t\tPrice\n");
     do{
        fread(&file_data,sizeof(struct book_type),1,fileSave);
          if(feof(fileSave)){
             break;
            }
          else{
             printf("%d\t\t%s\t%s\t$%2.2f\n",count,file_data->title,file_data->authorName,file_data->price);
             count++;
            }
       }while(!feof(fileSave));
     printf("\nPress enter to continue...");
     ch=getchar();
     getchar();
    }

# 2  
Old 04-22-2002
someone else might have a better answer than me; but when i used to C program (many years ago!) and had memory errors it was often because I tried to read (and write) into memory an amount larger than was allocated and ... a coredump!


Quote:
FREAD()

size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);

DESCRIPTION
The function fread reads nmemb elements of data, each size
bytes long, from the stream pointed to by stream, storing
them at the location given by ptr.
so, perhaps you have not allocated a large enough space that begins at the address in memory that your *ptr is pointing to.....
that would be my first guess....


the storage area (in memory) for file_data must be large enough to store the fread size from stream or you will get a memory error core dump..... how big is your memory area? did you initialize it or malloc some nice space?
# 3  
Old 04-23-2002
Hi

It seems like the core dump is generated at the 2nd printf statement inside your display_File_Data().

You have declared file_data as a pointer to the structure....but didnt allocate memory using malloc/calloc.

Do the necessary dynamic allocation and it should work this time.

Cheers
Deepa
# 4  
Old 04-23-2002
Hi

Just one more addition......

If you have gdb/dbx debugging tool in ur machine, u can get the exact statement where the core was dumped.

Cheers
Deepa
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