Replace arrays dynamically changing its memory

Question

I have multi-dimentional arr[3][4].

Then I allocate the memory for newArr[4][3] and change arr's rows into columns and columns into rows saving it to the newArr.

Is it possible to dynamically replace arr with newArr? A little example to clarify the situation:

#include <stdio.h>

void change(int[][4], int, int);

int main()
{
    int arr[][4] = {
        {1, 3, 2, 4},
        {3, 2, 4, 5},
        {9, 3, 2, 1},
    };
    change(arr, 4, 3);
    // now, there should be arr[4][3] = newArr

    getchar();
}

void change(int arr[][4], int cols, int rows)
{
    // create newArr array.
}

You need to use malloc and create a dynamic array.

Alok Save
– Alok Save

2013-01-19 13:30:17 +00:00
Commented Jan 19, 2013 at 13:30 — Alok Save
– Alok Save, Commented Jan 19, 2013 at 13:30

Oliver Charlesworth · Accepted Answer · 2013-01-19 13:29:27Z

2

No. You cannot change the size of a true array.

You would need to use dynamic allocation throughout in order to make this work. If you're unclear on how to dynamically allocate a multidimensional array, then please see e.g. http://c-faq.com/aryptr/dynmuldimary.html.

answered Jan 19, 2013 at 13:29

Oliver Charlesworth

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Comments

Kanwar Saad · Accepted Answer · 2013-01-20 03:02:47Z

Sure you can do that but in a slightly different way. With fixed size arrays you cannot do that. You have to do dynamic memory allocation and after that you can use the subscripts as you want. You just need to keep track what subscripts you are using currently to avoid errors.

#include <stdio.h>
#include<string.h>

void change(int **, int, int);

int main()
{
    int **arr = (int **)malloc(sizeof(int)*3*4);

    // Fill this memory in whatever way you like. I'm using your previous array
    // to fill arr.
    // Note that initial_arr is not your working arr. Its just for initialization
    int initial_arr[][4] = {
        {1, 3, 2, 4},
        {3, 2, 4, 5},
        {9, 3, 2, 1},
    };

    memcpy(arr, initial_arr, sizeof(int)*3*4);

    // You can access arr in the same way as you do previously. for example 
    // to print arr[1][2] you can write
    // printf("%d", arr[1][2]);


    change(arr, 4, 3);

    // now, simply copy newArr in arr. and you can subscript arr as arr[4][3]
    memcpy(arr, newArr, sizeof(int)*3*4);

    getchar();
}

void change(int **arr, int cols, int rows)
{
    // create newArr array.
}

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