add values in a 2 dimensional array using dynamic memory allocation

Question

Given this task:

Write a program that allocates the necessary amount of memory for storing the elements from two [m x n] integer matrices.

I don't know how to allocate memory to 2 Dimensional arrays.
I read some examples but I don't get it.

#define _CRT_SECURE_NO_WARNINGS
#include <conio.h>
#include <stdio.h>
#include <stdlib.h>
#define DIM 10


void main()
{
    int **m, *n;
    int i = 0, j = 0;
    int diml, dimc;;
    puts("Introduceti dimensiunea matricelor(linii|coloane)");
    scanf("%d%d", &diml, &dimc);
    m = (int**)malloc(dimc*sizeof(int));
    puts("Introduceti elementele primei matrici:");
    for (j = 0;j < dimc;j++)
    {
        m[i] = (int *)malloc(diml*(sizeof(int)));
    }
    for (j = 0;j < dimc;j++)
    {
        for (i = 0;i < diml;i++)
        {
            printf("tab[%d][%d]= ", j + 1, i + 1);
            scanf("%*d", m[j][i]);

        }
    }
    _getch();
}

My program crash after I enter the first line.

Introduceti dimensiunea matricelor(linhi I coloane)
3
3
Introduceti elementele primei matrici:
ab[1][1]= 2
ab[1][2]= 1
ab[1][3]= 2
ab[2][1]=

Problema 3.exe has stopped working
A problem caused the program to stop working correctly.
Windows  will  closethe program and notify you if a solution is
available.

m = (int**)malloc(dimc*sizeof(int)); --> m = malloc(dimc*sizeof(int*)); — Weather Vane
– Weather Vane, Commented Dec 29, 2015 at 17:43
1) m = (int**)malloc(dimc*sizeof(int)); --> m = (int**)malloc(dimc*sizeof(int*)); 2) m[i] = (int *)malloc(diml*(sizeof(int))); --> m[j] = (int *)malloc(diml*(sizeof(int))); 3)scanf("%*d", m[j][i]); --> scanf("%d", &m[j][i]); — BLUEPIXY
– BLUEPIXY, Commented Dec 29, 2015 at 17:44
Do not cast the result of malloc & friends in C. And there is no 2D array in your code! To alloc a 2D array, use int (*m)[DIMX_CONSTANT] = malloc(sizeof(*m) * y); — too honest for this site
– too honest for this site, Commented Dec 29, 2015 at 17:46
he/she will not be able to remove this if it will be answer. — BLUEPIXY
– BLUEPIXY, Commented Dec 29, 2015 at 18:07
Thank you guys for answering. @BLUEPIXY - Thank you sir, I followed your advice. My program works fine now. — RelaxedMind
– RelaxedMind, Commented Dec 29, 2015 at 18:08

Community · Accepted Answer · 2017-05-23 12:23:04Z

Avoid the mistake of allocating using the wrong size by allocating based on the size of the object and not the size of type. If the sizeof(int) was less then sizeof(int *), this would explain OP's problem.

// m = (int**)malloc(dimc*sizeof(int));   // Original
// m = (int**)malloc(dimc*sizeof(int *)); // corrected type
// m = malloc(dimc*sizeof(int *));        // cast not needed
m = malloc(sizeof *m * dimc);             // best : sizeof object

Use correct index j vs. i @BLUEPIXY. This is certainly an issue for OP.

for (j = 0;j < dimc;j++) {
  // m[i] = (int *)malloc(diml*(sizeof(int)));
  m[j] = malloc(sizeof *(m[j]) * diml);

Insure compiler warnings are fully enabled - it should have caught this one.
```
// scanf("%*d", m[j][i]);
scanf("%d", &m[j][i]);
```

Suggest checking the results of malloc() and scanf().

#include <stdlib.h>

m[j] = malloc(sizeof *(m[j]) * diml);
if (m[j] == NULL && diml != 0)) {
  fprintf(stderr", "Out of memory\n");
  return EXIT_FAILURE;
}

if (scanf("%d", &m[j][i]) != 1) {
  fprintf(stderr", "Non-numeric input\n");
  return EXIT_FAILURE;
}

main() should return int.

#include <stdlib.h>
int main(void) {
  ...
  return EXIT_SUCCESS;
}

When promoting, insure output gets printed and is not buffered. Use fflush() or end the prompt with '\n'.
```
   printf("tab[%d][%d]= ", j + 1, i + 1);
   fflush(stdout);  // add
   scanf(...
```

Embedded Software Engineer · Accepted Answer · 2015-12-29 18:21:02Z

0

You should allocate like this at first:

m = (int**)malloc(dimc*sizeof(int*));

After that you allocate like that:

m[i] = (int *)malloc(sizeof(int));

answered Dec 29, 2015 at 18:21

Embedded Software Engineer

4,9448 gold badges44 silver badges62 bronze badges

Collectives™ on Stack Overflow

add values in a 2 dimensional array using dynamic memory allocation

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related