Array overflow

[soulredemption]

Hi peoples...

I was wondering about an occurence i had regarding some code i was writing.

I am writing a basic library catalogue system for a uni assignment and had the following question (see code below):

after i create a array of structures, i read them in from a file. then when i add a new structure to the array from user input, it seems to tack it onto the end of the array fine, even though i havent created the necessary memory for it... i was wondering why this is happening?

code:

#define MAXLENGTH 30
// data structure:
struct book
{
   char title[MAXLENGTH];
   char authFirstName[MAXLENGTH];
   char authSurname[MAXLENGTH];
   int pubYear;
   float replacementCost;
};


// open the file.
FILE *openFile(char *fileName, char mode)
{
   FILE *openedFile;

   openedFile = fopen(fileName, &mode);

   if(openedFile == NULL)
   {
      printf("File '%s' not opened correctly.\n", fileName);
   }else
   {
      printf("File '%s' opened correctly.\n", fileName);
   }

   return openedFile;
}

// read the contents of the file
void readFile(FILE *openedFile, struct book *bookDB, int iNumOfBooks)
{
   int i;

   for(i = 0; i < iNumOfBooks; i++)
   {
      fgetc(openedFile); // <-- picks up the last \n char to start the fgets
      fgets(bookDB[i].title, MAXLENGTH, openedFile);
      fscanf(openedFile, "%s", bookDB[i].authFirstName);
      fscanf(openedFile, "%s", bookDB[i].authSurname);
      fscanf(openedFile, "%d", &(bookDB[i].pubYear));
      fscanf(openedFile, "%f", &(bookDB[i].replacementCost));
   }
}

// add a new book:
int newBook(struct book *bookDB, int iNumberOfBooks)
{
   printf("Adding a book to the collection...\n");
   printf("Title:: ");
   fgets(bookDB[iNumberOfBooks].title, MAXLENGTH, stdin);
   printf("Auther firstname:: ");
   scanf("%s", bookDB[iNumberOfBooks].authFirstName);
   strcat(bookDB[iNumberOfBooks].authFirstName, ",");
   printf("Auther Surname:: ");
   scanf("%s", bookDB[iNumberOfBooks].authSurname);
   printf("Year of Publication:: ");
   scanf("%d", &(bookDB[iNumberOfBooks].pubYear) );
   printf("Replacement Cost:: ");
   scanf("%f", &(bookDB[iNumberOfBooks].replacementCost) );

   iNumberOfBooks++;
   return iNumberOfBooks;

}

// call to open the file, read the file and add a new book:

printf("Please enter a filename to open:: ");
scanf("%s", fileName);

openedFile = openFile(fileName, 'r'); // opens a file

fscanf(openedFile, "%d", &iNumberOfBooks); // gets the number of books from file.

bookDB = (struct book*) malloc(sizeof(struct book)*iNumberOfBooks);

readFile(openedFile, bookDB, iNumberOfBooks);

fclose(openedFile);

iNumberOfBooks = newBook(bookDB, iNumberOfBooks);

Sorry about the long windedness of the code, but i wasnt sure what you would/wouldnt be needed.

any comments would be very welcome.

Thanks!
Joel aka SoulRedemption.

[quzah]

If your program doesn't crash when you stick something in some space you haven't allocated, it's just luck on your part. Don't rely on it, just fix it.


Quzah.

[soulredemption]

Heh, thanks. Thats just what i thought. Now, about fixing it, im assuming that would be to re allocate enough memory using malloc? or using a linked list or something?

Im not sure - i dont have that much exp with this...

cheers
Joel