Returning a 2d array of chars

Question

So I am writing a program that will encrypt a 2D array of chars in a function by passing a 2d array to it, but I am struggling to return it to main so I can use it other functions such as encrypt again to encrypt it twice.

char *encrypt(char bob[6][6], int key[6])[6][6]
{
int i ,j;
char tempArr[6][6];
printf("\n");
for (i = 0; i < 6; i++) {

    for (j = 0; j < 6; j++)
    {
        int col = key[j];
        printf("%c", bob[i][col]);
         tempArr[i][j] = bob[i][col];
    }

    printf("\n");
}
for (i = 0; i < 6; i++) {
    for (j = 0; j < 6; j++)
    {
        printf("%c", tempArr[j][i]);
    }
    printf(" ");
}

return tempArr;

}

this is my encrypt function that I am trying to return a string/2d array from **tempArr = encrypt(bob, key); encrypt(tempArr, key); and this is how I am passing the data through to that function

Honza Dejdar · Answer 1 · 2016-11-20T16:24:36.613

0

You are returning local variable from a function, which is destroyed by the ond of the function. You have to allocate it dynamically, using malloc(). You can do it like this: char **tempArr = malloc(6 * sizeof(char *)); for (i=0; i<6; i++) tempArr[i] = malloc(6 * sizeof(char)); This will dynamically allocate space for 6x6 array of chars. Don't forget to free() it when you are done with it.

edited Nov 20 '16 at 16:24

answered Nov 20 '16 at 15:54

Honza Dejdar

947
7
19

Can you give me an example please – Elliott Bailey Nov 20 '16 at 15:55
I added it to the answer. – Honza Dejdar Nov 20 '16 at 15:59
Does it go in the main or the function – Elliott Bailey Nov 20 '16 at 16:03
To the function, instead of `char tempArr[6][6];` – Honza Dejdar Nov 20 '16 at 16:04
I've done that that doesn't work sadly – Elliott Bailey Nov 20 '16 at 16:05
@ElliottBailey I think what Honza means is that the `malloc` call should go in your `encrypt` function and the call to `free` should be in `main` – babon Nov 20 '16 at 16:06
I am gonna need more that just "it doesn't work" to help you. – Honza Dejdar Nov 20 '16 at 16:06
This doesn't allocate 2D array but rather an array of pointers – SomeWittyUsername Nov 20 '16 at 16:07
Sorry it doesn't return, when i put a breakpoint in it has not got anything in the return. – Elliott Bailey Nov 20 '16 at 16:09
That isn't a 'statically allocated array'; that is a local variable that is not `static`. If it were `static`, it would solve one set of problems and create a new set of other problems (related to "only one set of results can be stored in an array at any given time"). – Jonathan Leffler Nov 20 '16 at 16:22
Sorry, you are right, I used wrong term. I will edit it now. – Honza Dejdar Nov 20 '16 at 16:23

Returning a 2d array of chars

1 Answers1