Array of array of strings in C

Question

In C, in a array that looks something like

{{"gsga","baf"},{"ad","aasb","asdf","asdfsd"},{"ads","sd","sd"}}

How to get different types of lengths such as:

to get the total size of array (in this example it is 3 because it contains 3 arrays of strings)
how to get size of any array within this array (for example size of 2nd array of this array is 4 since the second array contains 4 elements namely "ad","aasb","asdf","asdfsd"
how to get size of individual strings of any array (for example the size of 2nd string of 2nd array (i.e. "aasb") is 5).

What have you tried/researched? There are answers to all three of your examples on Stack Overflow already. — Jonny Henly
– Jonny Henly, Commented Apr 23, 2016 at 5:46
When dealing with ragged arrays, a common idiom is a sentinel value. — user3386109
– user3386109, Commented Apr 23, 2016 at 5:47
"how to get size of individual strings" You probably know that you can get the length of strings with strlen, which requires the strings to be null-terminated. It is not quite clear what you need your arrays for, but you could terminate your other arrays with NULL, too and implement a length function similar to strlen. (Of course, the terminator would then be a null pointer, not a null char.) — M Oehm
– M Oehm, Commented Apr 23, 2016 at 5:47
In short you can't get size of an array in C. For size of string, use strlen — SwiftMango
– SwiftMango, Commented Apr 23, 2016 at 6:03
Are you operating on the array of strings within the same scope where the array was declared? And is it an array, or are we talking about pointer-to-pointer-to-char?? — David C. Rankin
– David C. Rankin, Commented Apr 23, 2016 at 6:13

David Ranieri · Accepted Answer · 2016-04-23 09:44:04Z

4

You can get the size of all dimensions (3 x 4 x 7) using the sizeof operator.

If you want to know the length of the last one, use strlen in a loop:

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

int main(void)
{
    char data[][4][7] = {{"gsga","baf"},{"ad","aasb","asdf","asdfsd"},{"ads","sd","sd"}};
    size_t items1 = sizeof data / sizeof data[0]; /* size of dim 1 */
    size_t items2 = sizeof data[0] / sizeof data[0][0]; /* size of dim 2 */
    size_t iter1, iter2, count, len;

    printf("%zu items\n", items1);
    for (iter1 = 0; iter1 < items1; iter1++) {
        count = 0;
        printf("Item %zu\n", iter1);
        for (iter2 = 0; iter2 < items2; iter2++) {
            len = strlen(data[iter1][iter2]); /* size of dim 3 */
            if (len > 0) {
                printf("\tSubitem %zu: %zu characters\n", iter2, len);
                count++;
            }
        }
        printf("\t%zu subitems\n", count);
    }
    return 0;
}

Output:

3 items
Item 0
    Subitem 0: 4 characters
    Subitem 1: 3 characters
    2 subitems
Item 1
    Subitem 0: 2 characters
    Subitem 1: 4 characters
    Subitem 2: 4 characters
    Subitem 3: 6 characters
    4 subitems
Item 2
    Subitem 0: 3 characters
    Subitem 1: 2 characters
    Subitem 2: 2 characters
    3 subitems

data can be also declared as

char *data[][4] = {{"gsga","baf"},{"ad","aasb","asdf","asdfsd"},{"ads","sd","sd"}};

But then you need to check for NULL's to get the number of (non empty) subitems:

    for (iter2 = 0; iter2 < items2; iter2++) {
        if (data[iter1][iter2] != NULL) {
            len = strlen(data[iter1][iter2]);
            ...
        }
    }

Full Code

edited Apr 23, 2016 at 9:44

answered Apr 23, 2016 at 6:49

David Ranieri

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2 Comments

David Ranieri Over a year ago

No problem ;), but I am curious, how to check the stack with valgrind?

alk Over a year ago

SGCheck: an experimental stack and global array overrun detector: valgrind.org/docs/manual/sg-manual.html

August Karlstrom · Accepted Answer · 2016-04-23 07:49:16Z

0

The following program prints the values you mention:

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

#define LEN(arr) ((int) (sizeof (arr) / sizeof (arr)[0]))

int main(void)
{
    const char *A[][4] = {{"gsga", "baf"}, {"ad", "aasb", "asdf", "asdfsd"}, {"ads", "sd", "sd"}};

    printf("%d\n", LEN(A)); /*number of rows*/
    printf("%d\n", LEN(A[0])); /*number of columns*/
    printf("%d\n", (int) strlen(A[1][1]) + 1); /*size of element*/
    return 0;
}

edited Apr 23, 2016 at 7:49

answered Apr 23, 2016 at 7:10

August Karlstrom

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8 Comments

alk Over a year ago

Nitpicking: The %d is not nice.

August Karlstrom Over a year ago

@alk What do you suggest for ANSI C89?

alk Over a year ago

At least an unsigned type. But why C89 at all?

alk Over a year ago

Also the code does not take into account that there might "strings" larger then A[1][1].

August Karlstrom Over a year ago

@alk Of course there might be strings larger than A[1][1], what was asked for was "the size of individual strings".

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