creating a 2D array out of an array of string pointers in C

Question

This is an extension to my previous query - array of string pointers in C

I have this working sample code in C

int main(void)
{
    char *array1 = "12345";
    char *array2 = "abcde";
    char *array3 = "67890";
    char *array4 = "fghij";

    char *array_2d[4];

    array_2d[0] = array1; 
    array_2d[1] = array2; 
    array_2d[2] = array3;
    array_2d[3] = array4;

    int i,j;

    for(i = 0; i<=3 ; i++ ) {
        for(j = 0; j<=4 ; j++) {
            printf("%c", array_2d[i][j]);

        }
    printf("\n");
    }

}

I would like to de-reference

*array1 to *array4

i.e.

array_2d[0] -> "12345" 
....
array_2d[3] -> "fghij"

and not

array_2d[0] -> array1 -> "12345"
....
array_2d[3] -> array4 -> "fghij"

Is this possible ? I would maybe like to increase array_2d to [8] and say

array_2d[4] -> array1 -> "ABCDE"
....
array_2d[7] -> array4 -> "FGHIJ"

I hope this seems clear....

EDIT -

I think i got it. This is what i was trying to do.

char *array1 = "12345";
char *array2 = "abcde";
char *array3 = "67890";
char *array4 = "fghij";

char *array_2d[8];

array_2d[0] = array1; 
array_2d[1] = array2; 
array_2d[2] = array3;
array_2d[3] = array4;

array1 = "AAAAA";
array2 = "BBBBB";
array3 = "CCCCC";
array4 = "DDDDD";

array_2d[4] = array1; 
array_2d[5] = array2; 
array_2d[6] = array3;
array_2d[7] = array4;

I don't understand what you're asking. array_2d is not a 2D array at all - it's a 1D array of pointers. What does your notation array_2d[0] -> array1 -> "12345" mean? — Carl Norum
– Carl Norum, Commented Jul 3, 2013 at 20:13
Your situation now is array_2d[0] -> "12345", not array_2d[0] -> array1 -> "12345". So you have achieved exactly what you want. — Kamen Stoykov
– Kamen Stoykov, Commented Jul 3, 2013 at 20:17
I would like that array_2d[0] copies "12345" from array1, so i can empty array1 and store(point) "ABCDE" , then array_2d[4] copies "ABCDE" from array1. — Sid5427
– Sid5427, Commented Jul 3, 2013 at 20:19
You can't modify the array that array1 points to, because it's a literal. You can reassign array1 to point to a different array, that doesn't affect array_2d[0]. — Barmar
– Barmar, Commented Jul 3, 2013 at 20:22
@KamenStoykov , so if i directly just re-assign say *array1 = "ABCDE" and then say array_2d[4] = array1. It should should work ? — Sid5427
– Sid5427, Commented Jul 3, 2013 at 20:23

Barmar · Accepted Answer · 2013-07-03 20:28:29Z

4

Based on the comments, I think this is what you're asking about.

int main(void)
{
    char *array1 = "12345";
    char *array2 = "abcde";
    char *array3 = "67890";
    char *array4 = "fghij";

    char *array_2d[8];

    array_2d[0] = array1; 
    array_2d[1] = array2; 
    array_2d[2] = array3;
    array_2d[3] = array4;

    array1 = "ABCDE";
    array2 = "GHIJK";
    array3 = "LMNOP";
    array4 = "QRSTU";

    array_2d[4] = array1;
    array_2d[5] = array2;
    array_2d[6] = array3;
    array_2d[7] = array4;

    int i,j;

    for(i = 0; i<=7 ; i++ ) {
        for(j = 0; j<=4 ; j++) {
            printf("%c", array_2d[i][j]);
        }
    printf("\n");
    }
}

Reassigning array1 doesn't affect what array_2d[0] points to. The original assignment just copies the pointer, it doesn't make them aliases for each other.

edited Jul 3, 2013 at 20:28

answered Jul 3, 2013 at 20:17

Barmar

789k57 gold badges554 silver badges669 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Sid5427 Over a year ago

Yup exactly what I was asking.

Mark Wilkins · Accepted Answer · 2013-07-03 20:24:36Z

1

Like others have said, it is not completely clear to me what is being asked, but it is possible to make copies of the strings as follows (this is just one possible way):

char *array_2d[8];

array_2d[0] = strdup( array1 ); 
...
array_2d[4] = strdup( array_2d[1] ); 
strupr( array_2d[4] );
...

This will result in putting separately allocated strings in each location. strdup makes a copy of string. Note that you have to call free() (e.g., free( array_2d[0] );) to free that memory.

Another thing to note: The OP seems to indicate that you plan to modify the array (string) pointed to by array1. You cannot change that memory (it is a string constant). You can change what array1 points to, though.

answered Jul 3, 2013 at 20:24

Mark Wilkins

41.3k5 gold badges61 silver badges111 bronze badges

Collectives™ on Stack Overflow

creating a 2D array out of an array of string pointers in C

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related