2D Array using Command Line Argument and Dynamic Memory Allocation in C-CodePudding

So I wanna create a 2D array where the number of rows and columns are taken by command line argument. Then the array is made using dynamic memory allocation where users give the input.

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

int main(int argc, int *argv[]) {
   int **arr;
   arr = (int **)malloc(*argv[1]*sizeof(int*));
   
   for (int i=0; i<argv[1]; i  )
      arr[i] = (int *)malloc (*argv[2]*sizeof(int));
  
   for (int i=0; i<argv[1]; i  )
      for (int j=0; i<argv[2]; j  )
         scanf("%d", &arr[i][j]);
   
   for (int i=0; i<argv[1]; i  ){
      for (int j=0; i<argv[2]; j  )
         printf("%d ",arr[i][j]);
      printf("\n");}
   
   return 0;
}

However Iam getting segmentation dump every time Iam running this. Can you please explain where Iam doing wrong.

CodePudding user response：

You have an incorrect signature for main. Arguments are provided as an array of pointers to string, so to get the row/col, you need to convert the string to int, for example, using atoi().

You also have an error using i for the second part of the loop when calling scanf.

I've made corrections below and added some minor changes for clarity.

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

int main(int argc, char *argv[]) {
   int **arr;
   if (argc < 3) {
       printf("must supply 2 integer arguments\n");
       return -1;
   }
   
   int rows = atoi(argv[1]);
   int cols = atoi(argv[2]);
   
   printf("rows=%d, cols=%d\n", rows, cols);
   arr = (int **)malloc(rows*sizeof(int*));
   
   for (int i=0; i<rows; i  )
      arr[i] = (int *)malloc (cols*sizeof(int));
  
   for (int i=0; i<rows; i  ) {
      for (int j=0; j<cols; j  ) {
         printf("Value for row %d col %d: ", i 1, j 1);
         scanf("%d", &arr[i][j]);
      }
   }
   
   for (int i=0; i<rows; i  ) {
      for (int j=0; j<cols; j  ) {
         printf("%d ",arr[i][j]);
      }
      printf("\n");
       
   }
   
   return 0;
}

CodePudding user response：

Use array pointers.

int main(int argc, char *argv[]) 
{
   
   int rows = atoi(argv[1]);
   int cols = atoi(argv[2]);

   int (*arr)[cols] = malloc(rows * sizeof(*arr));
   
}