How can I put a null value for char** str

Question

How can I put a null value for char** str because im having and Error of "Dereference of out of bound pointer: 1 bytes(1element) past end of array im using C language"

while(part)
    {
        res = (char**)realloc(res, (i + 1) * sizeof(char*));
        *(res + i) = mystrdup(part);

        part = mystrdup(strtok(NULL, delim));
        i++;
    }
    res = (char**)realloc(res, i * sizeof(char*));
    *(res + i) = NULL; // This is where I Encounter the ERROR

[Please see this discussion on why not to cast the return value of `malloc()` and family in `C`.](http://stackoverflow.com/q/605845/2173917). — Sourav Ghosh, Jan 13 '16 at 10:37
Isn't it like after the `realloc()`, `*(res + i) = NULL;` should be `*(res + i -1) = NULL;` or am I missing something? — Sourav Ghosh, Jan 13 '16 at 10:40
What do you mean with "null value"? The value `0x0`? A _null pointer_? — too honest for this site, Jan 13 '16 at 10:51
When I use *(res + i) = NULL i got an error of Dereference of out of bound but when I use *(res + i -1) = NULL if my last data inside the res[2] = C it will become null value, the only retain data will be in res[0] = A, res[1] = B. Then for the res[3]=NULL, because this *(res + i -1) = NULL will delete the last value of my array. That's what I get when I use this *(res + i -1) = NULL — Joebert Bisenio, Jan 15 '16 at 03:16

score 2 · Answer 1 · edited May 23 '17 at 12:23

2

In this part of code

res = (char**)realloc(res, i * sizeof(char*));
*(res + i) = NULL;

by trying to access *(res + i), you're going off-by-one. You should write

*(res + i -1) = NULL;

Having said that,

Please see this discussion on why not to cast the return value of malloc() and family in C..
A statement like pointerP = realloc (pointerP, .....) is considered very unsafe, as in case, if realloc() fails, you'll end up losing the actual pointer, too.
Always check for the return value of malloc() and family of functions against NULL to ensure the success.
Also, put a NULL check for the return value of strtok(), too before passing that to strdup().

edited May 23 '17 at 12:23

Community

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answered Jan 13 '16 at 10:42

Sourav Ghosh

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Thanks for the answer but if I will do this *(res + i -1) = NULL; the last data inside the array will be deleted. example: when: *(res + i) = NULL; res[0] = A res[1] = B res[2] = C res[3] = D but when *(res + i - 1) = NULL; res[0] = A res[1] = B res[2] = C res[3] = NULL – Joebert Bisenio Jan 14 '16 at 00:54

How can I put a null value for char** str

1 Answers1