This challenge from hackerRank that I was working on successfully compiles with the test run and gives out correct answers with all sorts of input. But when I submit and the code is run with enormous amount of digits like so, I get a segmentation fault.

My best guess is that I am making some sort of mistake while allocating memory to the dynamic 2D array.

Since all my test runs have successfully compiled and given out a correct result I have no idea why it would not work.

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

/*
 * This stores the total number of books in each shelf.
 */
int* total_number_of_books;

/*
 * This stores the total number of pages in each book of each shelf.
 * The rows represent the shelves and the columns represent the books.
 */
int** total_number_of_pages;

int main()
{
    int total_number_of_shelves;
    scanf("%d", &total_number_of_shelves);

    int total_number_of_queries;
    scanf("%d", &total_number_of_queries);

       //_______________________________________________________________________// 
      //       All malloc() declarations writen by me are here :               //
     //     My guess is, one of this statement is causing the bug.            //
    //_______________________________________________________________________//

         total_number_of_books=(int *)malloc(sizeof(int)*(total_number_of_shelves*1100));
      
         total_number_of_pages=(int **)malloc(sizeof(int*)*total_number_of_shelves);
       
         for (int tnos=0; tnos<total_number_of_shelves; tnos  ) 
         {     
              total_number_of_pages[tnos]=(int *)malloc(sizeof(int)*1100);
         }
    

   
    while (total_number_of_queries--) {
        int type_of_query;
        scanf("%d", &type_of_query);
        
        if (type_of_query == 1) {


            //___My code starts here.___//

            int x, y, index;
            scanf("%d %d", &x, &y);

            index=0;
            
            while( total_number_of_pages[x][index]!=0 ) 
            {
                index  ;
            }

            total_number_of_pages[x][index] = y;
            total_number_of_books[x]  ;    

 //_______________________________________________________________//     
//All code below is a template which was provided by the website.//

        } else if (type_of_query == 2) {
            int x, y;
            scanf("%d %d", &x, &y);
            printf("%d\n", *(*(total_number_of_pages   x)   y));
        } else {
            int x;
            scanf("%d", &x);
            printf("%d\n", *(total_number_of_books   x));
        }
    }

    if (total_number_of_books) {
        free(total_number_of_books);
    }
    
    for (int i = 0; i < total_number_of_shelves; i  ) {
        if (*(total_number_of_pages   i)) {
            free(*(total_number_of_pages   i));
        }
    }
    
    if (total_number_of_pages) {
        free(total_number_of_pages);
    }
    
    return 0;
}

CodePudding user response：

You should use realloc() to grow the dynamic arrays when you need to put a new element in them. In your code you're doing just one allocation at the start.

For instance, write this at the start (after you scanf() to get total_number_of_shelves and total_number_of_queries):

total_number_of_books = malloc(total_number_of_shelves * sizeof(int));
total_number_of_pages = malloc(total_number_of_shelves * sizeof(int*));

// TODO: you should initialize every element of the first array to `0`,
//   and every element of the second array to `NULL`

And when you need to put a new element inside, you use realloc():

total_number_of_books[x]  = 1;

total_number_of_pages[x] = realloc(total_number_of_pages[x], total_number_of_books[x] * sizeof(int));

...