All elements in an jagged array are zero on c-CodePudding

Let each row have a different size column, where all the elements are 0. I tried it on my own, and now my code just achieves zero for all elements with the same number of columns in each row. I wanted my code to allow the user to control the number of columns per row. How to achieve it on my code? Here is my code. #include <stdio.h> #include <stdlib.h>

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

int** make_zeros(int rows, int cols) {
    int** zeros_array; // create a double pointer nameed zeros_array
    zeros_array = malloc(sizeof(int)*rows); // set space for zeros_array
    for(int row = 0; row < rows; row  ) {
        zeros_array[row] = malloc(sizeof(int)*cols); // set space for zeros_array for each row
        for (int col = 0; col < cols; col  ) {
            zeros_array[row][col] = 0; // the element is equal to zero;
        }
    }
    // return the result
    return zeros_array;
}

int main(void) {
   printf("How many rows ?: "); // let user enter the nums of rows
   int rows = 0;
   scanf("%d",&rows);
   printf("How many columns ?: "); // let user enter the nums of cols
   int cols = 0;
   scanf("%d",&cols);
   int **zeros; // create a double pointer
   zeros = make_zeros(rows,cols); // lead to the function make_zeros
   for (int r = 0; r < rows; r  ) {
      for (int c = 0; c < cols; c  ) {
           printf("%d ",zeros[r][c]); // print the elements of all of array that stored on double pointer
       }
       printf("\n"); // move to the new line
   }
   return 0;
 }

Thank you all for your help.

CodePudding user response：

You're not allocating enough memory:

zeros_array = malloc(sizeof(int)*rows);

This allocates space for rows elements of type int. You need rows elements of type int *. On most systems, int is 4 bytes and int * is 8 bytes. So you end up writing past the end of allocated memory which triggers undefined behavior.

Specify the correct type you want to allocate space for:

zeros_array = malloc(sizeof(int *)*rows);

CodePudding user response：

You could use scanf inside your make_zeros function inside the for loop and ask the user to input number of columns in that particular row.